Brian E. Brzezicki
Copyright 2013
Version 1.00 04/06/2012

Disclaimer
Use this at your OWN risk, do NOT sue me if it breaks your board... if your doing this your board is probably already broken though ;)

Trouble shooting information

Game Board #1 March 2013

Problem: Missile command screen comes up, but no explosions, immediately resets, with dots going through the graphics Troubleshooting/dianosis steps: Put game into test mode, it says the POKEY is bad Swapped with a known good POKEY, same issue and still say POKEY is bad Probed the POKEY select pin on the POKEY, it's messed up Traced back to where POKEY select is driven from, noted the inputs did not match the outputs Removed chip, noted that somethign is still driving the POKEY select line Found POKEY select line shorted with an adjacent line, removed metal that was shorting the two wires Put POKEY back in Game works!

Game Board #2 April 23 2013

Problem: Missile command is missing bases Troubleshooting/dianosis steps: Put board into test mode, noted that one of the dip switches is physically broken, replaced Looked at color ROM, all pins that should be flipping are Went back to 74LS166 @ P6, noticed the output (pin 13) is stuck low Replaced 74LS166 @ P6 Everything works, P6 pin 13 is no longer stuck... game works for a while.. then stopped working. Noted that when things are not working, pin 13 at P6 is stuck low again Noted game is resetting, noticed voltage on my test bench is low, fixed voltage, everything works again.. for a while then stopped working...again Noted if I touch the crystal the game resets, replaced crystal, I think one of the legs was broken or lose Game stops resetting when I touch the crystal, but still no bases hit reset a few times, then the system locked up with a yellow screen...tried replacing the CPU incase the CPU is causing these wierd issues... no change ...got angry and went to bed Turn it back on the next day.. everything is working again properly Hooked up Fluke 9010A and ran long RAM test on entire memory region.. everything came back fine Reset the game a few times as this before caused it to lock up with a yellow screen... everything still working Noticed the game often resets, especially when resetting, get's into a reset loop, also noticed when hitting reset, sometimes the game will pause, give a yellow or color screen, and hang for a while before resetting, someetimes the screen will reset multiple times. Theorized that somethign is causing the watchdog to reset probably memory corruption. Replaced all big 100uf power capactitors on the board, seems to fixed the problem, game now seems stable and constantly hitting the reset button gives consistant clear resets Game fixed

Game Board #3 Aug 18 2013

Problem: When turned on there is just a solid yellow screen that shakes. Board just not do anything in self test mode. (same thing) Troubleshooting/dianosis steps: Pulled POKEY Tested memory with fluke (long RAM test), multiple bit errors Tested ROMs with fluke, verified expected signatures, except one ROM with legs fell off when I pulled it out to validate. Manually tried writing to address 0, bit errors seem to occur on bits 0,1,2 and 4, probing with a logic probe and looping on reading and writing to address 0, found bit 4 (4116 @ L4) had a dead output, bits 0,1 and 2 seemed to be stuck regardless of input (validated input pattern "sounded" the same) replaced chips for bits 0,1,2,4 and 7 now can write to memory address 0 ok getting DCD errors on bits 3,6 diagnosed the memory decoder circuit, replaced an LS157 and LS153, looks like the data from the 153s are OK, additional testing looks like the signals are getting there OK, perhap an issue with the write select circuitry? replaced two more of th 4116s, have to still run a full long RAM test, but memory issues seem to be gone now. Replaced PROMS at np1 and r1 with 2732s (double programmed) (one was broken, the other was the wrong PROM) "fixed" broken 6502 CPU by soldering pins onto broken pins and putting in a socket Board resets after playing for a while Replaced a 74LS14 that was old and used and put in a new 74LS14 Upgraded to version 3 code reflowed ROM socket solder Installed new 74LS244 and socket at NP/3 Installed new socket for CPU Board is now working!

Game Board #4 Aug 19 2013

Problem: When turned on there is just a solid colored screen. Board just not do anything in self test mode. (same thing) Troubleshooting/dianosis steps: Notcied 10Mhz crystal was missing, installed new crystal Pulled POKEY Tested memory with fluke (long RAM test), bit errors 0xD3 Replaced the 4116s corresponding to bit locates 0xD3 Did long fluke memory test for range 0x000-0xEFF, now getting DCD errors address bit 3 diagnosed the 4116 related to data bit 0x04 is bad, replaced getting new memory errors, replaced last 2 4116s board clears fluke long RAM test for addresses x0000 - 0x3FF Burned new ROMS (version 3) Sockets seem flakey, and one pin of one rom got bent putting it in board boots up to a white screen, no watchdog resetting Pulled ROMS board boots up to a white screen, still no watchdog resetting Examining counter at D4. Traced dead line back to pin 11 on D8, pulled chip, found chip is a 7474 NOT an 7400. socketed D8 and replaced, no change Found counter at D4 is not getting a 128H signal. Replaced counters (72LS191s) at A4 and B4, replaced counter (74LS93) at D4, verified that the watchdog circuitry is working. Game is booting up, but only showing yellow color and scrolling "Atari" text at bottom, in demo mode can see when missile shots got up but only a centimeter or so, and shot color is yellow. Traced from color RAM @ L7 back to 74LS175 @ C7 which had it's pin 10 (LO2COL) stuck low, removed, resocketed and replaced. Game is now working!

Game Board #5 Aug 23 2013
Problem: When turned on there is just a colored stripped screen Troubleshooting/dianosis steps: Pulled POKEY Pulled ROMs Tested memory with fluke (long RAM test), bit errors 0x40 Replaced the 4116s @ n4 which corresponds to data bit 0x40 Did long fluke memory test for range 0x000-0xEFF, OK Reinstalled ROMS and POKEY Board works!

Game Board #6 September 30 2013

Problem: When turned on there is just a colored stripped screen CPU socket plastic fell off when removing CPU, snapped back in, will probably want to replace that. Troubleshooting/dianosis steps: Pulled POKEY Did a RAM LONG test with Fluke 9010a, returned BTS 02 error, that's chip H4 manual read/write test shows bit is stuck high, verified with read loop value 0x00 that and logic probe that input (pin 2 @ H4) toggles correctly but output (pin 14 @ H4) is stuck high removed 4116 @ H4 and installed socket and new 4116 RAM Board passes RAM long test for range 0x0000 - 0x3FFF Board boots up fine and passes self test mode! Board works!

Game Board #7 October 22 2013
Problem: When turned on there is just a colored white screen Troubleshooting/dianosis steps: Did RAM long test on Fluke 9010a for range 0x0000 - 0x3FFF, got back RAM DCD error bit 8 verified writes to 0x0000 and 0x0200 were the same for all bits (which means it's not a RAM issue it's a addressing issue) Found 74LS244 on F2 was stuck high, replaced. Board works!

Game Board #8 November 12 2013

Problem: When turned on there is just this crazy multicolored zig-zag screen Troubleshooting/dianosis steps: Did a RAM long test on 0x0000-0x3FFF and immediately got back ALL BITS BAD, which is highly unlikely. Tried reading from a ROM location, got back 0xFF, tried another, same thing... this along with the memory points to an address decoding issue Tried reading RAM and ROM areas and checked the RAM and ROM select lines.. they didn't enable! Found a bad 7414 at position J6, socketed and replaced RAM now seems to be working, need to do a long RAM test. Put game into self test mode, got ROM 2 error, but OK sounds and RAM test pulled ROMS verfied in burner put ROMS back in game did fluke signature test, rom at JK1 was coming back bad with signature 0000 Replaced 74LS244 @ BC/1, no change tested voltage across ROM, was less than 1V, swapped into another position and tested, still bad burned new ROM and re-installed All ROMS verify OK Game Works!

Game Board #9 November 13 2013
Problem: Game seems to work and pass self tests, but the video is all snowy, and messed up and shifted 1/2 into the screen horizontally, additionally monitor has a wierd sound Troubleshooting/dianosis steps: Resocketed a couple chips (3) and tried replacement chips in timing circuits Found bad 7474 @ A9, socketed and replaced witha 74LS74 Game works!

Game Board #10 December 23 2013

Problem: Junk on screen, game not playing Troubleshooting/dianosis steps: Verified Clock signal Game is resetting performed long RAM test with Fluke 9010A on 0x000 -0x3FFF - OK Verified ROMS in burner, noted sockets are lose and some ROMS had bent pins, but Game still did not work after straigtening ROM legs Pull 6502 CPU, found it came out way to easy Put in new 6502, games worked tested OLD 6502 in another game with ZIF socket, it worked Pull old CPU back, game did not work, noted it went it way too easy and seemed lose Looked at socket, looked liek pins are white in some areas removed CPU socket, noticed green corrosion underneath socket, cleaned off with rubbing alcohol and toothbrush Soldered on new socket Put back original (old) CPU Game works!

Game Board #11 December 24 2013
Problem: Game dead Troubleshooting/dianosis steps: Noticed crystal was missing, replaced game works!

Game Board #12 December 29 2013

Problem: Game reported dead Troubleshooting/dianosis steps: Noticed crystal was missing, replaced Edge connector had dirt and solder on traces, desoldered, found a bunch of pads completely lifed. Put on new edge connectors Verified ROMS, found 2 bad ROMS, replaced Did fluke long RAM test immediately found bits 0x10 (4114 @ L4) and 0x80 (4116 @ P4) bad, replaced Did another long RAM test, got DCD errors, did some testing found 2114 @ M4 to be likely bad, replaced Board boots and tests OK, now but missing the color of the BASES. Seems similar to a problem I had on another board where ONLY the bases where there! After tracing back chips from P6 found bad 7474 @ A7, replaced Game works!

Game Board #13 March 10 29 2014
Problem: Game is dead Troubleshooting/dianosis steps: Fluke RAM long tests shows bit 2 is dead. Replaced, no change After much work, found that a reistory between the write enable control and the RAM was broken, but not visibly noticible. Game works!

Game Board #14 March 10 29 2014
Problem: Game is dead Troubleshooting/dianosis steps: Fluke RAM long tests shows bit 5 is dead. Replaced, no change Found bad 74LS244 Game works!

Game Board #15 March 14 2014

Problem: Game is dead Troubleshooting/dianosis steps: BUS test failed multiple errors ROM test succeeded reading RAM at 0x0000 showed fluxuating numbers, looks like somethign is writing to the databus along with the RAM.. probalby a ROM Found programmmemory1 line was being actived Found a bridged trace on sockets near B5 and C5, resocket, BUS test succeeded RAM test failed with BTS 0x0C Found those chips where not getting the write signal Traced problem back to socketed PROM at L6, no continutity between output pins and WE pins. Removed old socket, put in new socket. Game works! Game works!

Game Board #16 March 25 2014
Problem: Wierd lines in graphics Troubleshooting/dianosis steps: Fluke ROM long test succeeded Replaced 74LS10 @ R5 - no change Cut power to 74LS125 - lines went from stripped to solid blue Replaced 74LS125 @ R6 - no change Pulled 7575 @ R7 - no change, put in socket and put back original Replaced 74LS153 @ P7 - fixed! Game works!

Game Board #15 March 18-23 2014

Problem: Game is dead Troubleshooting/dianosis steps: Fluke ROM long test succeeded Put game into test mode got ROM2 error pulled all ROMs, labeled with Fluke signature and tested Found ROM2 was bad, (all 0xFFs) Burned a new ROM and replaced Game boots up but when trying to enter test mode would constantly reset Reverified all ROMS, all succeeded except last ROM (range 0x7800 - 0x7FFF), it would read different each time pressed down on ROM socket for the last ROM, it passed fluke test and booted Removed socket and installed a new socket Game works!

Game Board #16 March 5/3 2014

Problem: Game is dead Board has had all 4116s pulled and socketed Troubleshooting/dianosis steps: Fluke gives RAM error on BTS 0x40 all addresses Tried swapping out known good RAMs to no avail Used oscope tnd fluke 9010a in a write loop at address 0x0000 to find that the chip that holds the data for D6 (N2) has all kinds of other signal on there Found a small solder glob connecting the trace for the data input bit connectting to the pin for A0 (pin 5) on the chip at N2, removed the solder glob. No longer getting RAM BTS 0x4000 errors

Game Board #17 March 8/5 2014

Problem: Game is dead Screen is solid yellow Troubleshooting/dianosis steps: Verified +5V power Attached Fluke 9010A 6502 POD, it failed to connect. Assuming the POD is working this usually means Bad +5V power or Bad clock Probed pin #37 on 6502 socket (clock input) this is what I got That's not a proper clock signal. Verified signals from clock through D6, D5 and E5 where good (10Mhz -> 1H -> 128H -> HBLANK) Decided to look backwards from the CPUs side, noted input into pin #2 @ C4 was not what it should have been (it should have been about 1.25Mhz) Went backwards from there, noted circuit consist of 7474 @ A7, 74S74 @ B8 and 74S00 @ A8. checked A7 with logic comparator, looked bad, checked 74S75 @ A8 looked good, checked 74S00 @ A8, looked good. Replaced 7474 @ A7 with 74LS74 (don't have any 7474 but the 74LS74 is a modern replacement. Now there is a good clean 1.25Mhz signal on pin #37 on the 6502 CPU Game works!

Game Board #18 March 2/8 2015

Problem: Game plays blind, owner reported there monitor had blown out other games syncs. Troubleshooting/diagnosis steps: Measured VSYNC line, it was all off. Looked at input to 74LS08 @ H7 pin #9, signal looked good, Looked at input to 74LS08 @ H7 pin #10 (VBLANK), signal looked good Looked at output of 74LS08 @ pin 8, all messed up Removed 74LS08 @ H7, noted there was still a signal on pin #8 (there should not have been as the chip creates the output signal on pin #8 Tracked the trace from pin 8 to J7 which had been previously replaced by owner. Noted pin #12 was tied to pin 8 on J7 (it should not be) replaced socket on J7 put back chips from H7 and J7 Game works!

Game Board #19 March 08/09/2015

Problem: Game is dead Troubleshooting/dianosis steps: Noticed that LCD on test bench was not syncing Touched crystal, it was clear that it was broken, rattled and was lose when touched, replaced LCD now syncs however game is not working correctly, sometimes get garbage on screen that disappears, pressing ROMS changes sometimes. Did Fluke 9010A ROM test on all rom ranges, found JK1 did not give correct reading, pressed down then got correct reading. Removed all 6 ROM sockets and replaced, game boots now! Trackball however does not work, no movement at all Replaced MC14584 @ C9 just because that's usually the issue and I didn't have a way of spinning the trackball and measuring out output at the same time. No change, put back original chip @ C9 I did not have a way of probing the circuit while I moved the trackball so I wanted to try to isolate the possible chips simply by using logic. There is only a few chips in the trackball circuitry. 74LS157 @ D9, 7474 @ J8, 74LS191 counter at K8 (verticle), 74LS191 at K9 (horizontal) 74LS244 @ L9. Now counters usually are common failures, howevever there are 2 counters eone controlling the horizontal and one the vertical direction. it's unlikely they BOTH went bad at the same time (since NO direction works). J8 is used by both of the direction circuits so it could be a failure, and also a common failing chip. However 74s are fairly easy to check as for each output there is an inverted output, so if you measure both outputs at the same time and they are OPPOSITES this chip is usually working (especially if the outputs changes over time. In this case the chips inputs were static indicating no input, and the outputs WERE inverted, so it was unlikely it was this chip. the 74LS157 @ D9 also can effect both directions. The 74LS157 is a quad dual input multiplexer. A dual input multiplexer has 2 inputs and 1 output. When the chip is enabled (pin 15 is ground) and the select (pin 1) is also at ground, then the output will match the first input. On Missile Command in upright mode the enable and select with both be at ground, so the input and the output should match. However when measuring input 1 (pin 2) and output 1 (pin 5) I found them to NOT match. I pulled the chip and put in a new socket and replaced. Now the trackball works! Game works!

Game Board #20 08/2015

Problem: Game is dead Troubleshooting/dianosis steps: Noticed crystal is missing, replaced saw 3 really really bad 25V @ 100U caps, replaced just for good measure cap at c4 is broken in half, replaced chip is CPU socket is 40 pins, but doesn't even look like a 6502s label of any 6502 I've ever seen, label is faded out. tested CPU in another known working board and it did not work, replaced getting just a flashing screen did a RAM long test with Fluke 9010A in RAM range 0x0000 - 0x3FFF, all addresses give BTS 0x20 error, testing that bit is always low found bad prom @ L6, replaced RAM now is OK, game boots, but sounds are scratchy and quiet Replaced LM324 Game works!

Game Board #21 10/7/2015

Problem: Garbage on screen, the garbage changes ever so often Troubleshooting/dianosis steps: check reset line (pin #40 of CPU) it is watchdogging checked CPU clock (pin #37 it's OK at about 1.25Mhz) did RAM long check with Fluke 0x0000 - 0x3FFF - OK pulled out all ROMs and tested with ROM reader - all OK, MC version 2 put ROMS back in game and tested with the Fluke. The first 5 ROMs (0x5000 - 0x77FF were OK) Howver the last ROM (R1, 0x7800 - 0x7FFF) was getting bad checksum from the CPUs standpoint. Did a read at address 0x7800 in looping mode, the low byte was changing... something is interfering on the bus when only the ROM should be talking. Pulled ROM and tested again, signal was stable Pulled POKEY, no change, but found cut trace under POKEY removed POKEY socket, fixed trace and put on new socket one at a time removed and replaced a few 74LS244s that tie directly to the unbuffered data bus to try to isolate the bus issue, to no avail. noticed owner had replaced sockets at C11, C9 and M9, pulled sockets, found a few bridged traces under the sockets repaired after testing for a while game lost it's yellow Found the color ram (82S25 @ l7) was never getting a write signal (write stuck high pin #3) trace back to find what generates the color ram write, it's 74LS42 @ E8, it was bad, replaced Game works!

Game Board #22 10/6/2015

Problem: Game does not work Nothing on screen LCD monitor is syncing Troubleshooting/diagnosis steps: reset pin #40 on CPU is transitioning ROMS have been replaced with machined sockets... argh. Running fluke RAM long - ok read roms on programmer and then verified with ROM test on fluke - OK disabled watchdog and game boots up but with wierd color pattersn on the top and bottom. watchdog is never getting a clear signal reset game and not colors are bad looked at address decoding circuit to see what triggers the watchdog write, ls42 @ l8, definitely looks bad, replaced Game works!

Game Board #23 10/11/2015

Problem: Game does not work LCD monitor is NOT syncing Game board seems to be hacked up with many poor repair attempts Troubleshooting/diagnosis steps: Fluke long 0x0000 - 0x3FFF gives BTS errors 0xFF Read with loop on 0x0000 shows all digits changing. must be bus issues ROMs checks with Fluke are OK Checked address decoders @ e8 and n2 both seem to be OK H and V sync chains seem OK found machined socket @ f4, carefully removed, horribly damanged traces EVERYWHERY fixed traces and added socket removed socket @ L6 and replaced just because game boots up now but wierd little dots near the missile counters on the bases Fluke long on RAM 0x0000 - 0x3FFF shows BTS error 0x40 starting at address 0x0300, this is 4116 @ N4 Verified with read and write loops that write signal is correct while looping read and write at address 0x0300 Pulled N4, socketed and replaced Game works!

Game Board #24 11/11/2015

Problem: Game does not work, solid yellow screen with white "noise" on top 15% of screen Game is missing the CPU Game board seems to be hacked up with many poor repair attempts Troubleshooting/diagnosis steps: Did Fluke long RAM on RAM range 0x0000 - 0x3FFF, got back BTS errors immediately, BTS errors changed for each address Did a looping read on 0x0000, both digits were changing rapidly, meaning the bus is messed up most likely Noted all RAM chips had been socketed, some looked questionable, note to self, will look at this more once I do other tests. Did ROM test to try to isolate bus issues to the RAM, ROM tests came back fine, which leads me even more to believe there is damaged to the socketed RAMS. Made sure address decoders at e8 and n2 were ok, they had been previously pulled. tested with HP 10529A and oscope in looping read, both looked fine Pulled both e8 and n2 and did a looping read on 0x0000, stable at 0xFF put back n2 and did a looping read on 0x0000, back to being messed up Pulled POKEYs no change, wasn't expecting a change, but figured good to rule out pulled ROMS, again not expecting a change but it's easy to test, still having issues with looping read @ 0x0000 Pulled RAMS out of sockets, starting to check continuity of pins that are common and also to make sure there were not continuity on pins that should not be connected, found pin #4 and #13 are tied on the RAMS, which means there's got to be a bridged trace under one of these replaced sockets. used Hakko 808 to remove solder on pins #4 and #13 on each ram, still got continuity Pulled 4 the sockets that looked the most questionable after looking carefully at multiple angles to look for bridges underneath sockets. Found M4 had some damaged and smashed together traces, fixed. verified bridge fixed, checked for more bridges, didn't find any replaced pulled sockets Reinserted RAM Fluke passes RAM tests, and game boots with Fluke in it Put in replacement CPU (CPU was initially missing) Game works!

Game Board #25 11/15/2015

Problem: This board was a PAIN with MULTIPLE failures Game does not work LCD test monitor is not syncing Troubleshooting/diagnosis steps: clock looks good, no reset either pulled cpu then got reset, game must be playing blind checking sync circuits, horizontal OK b4 has been previously socketed with a machined pin and has a bad signal on #2.. mixed signal need to investigate. pulled chip from socket, its got a signal 2Khz on pin #2, it should not have any which means there is a bridge somewhere. probing other pins and signal lines near the chip doesn't look like its a bad solder job on the socket, will verify with continuity test. found a trace back to B7 where the chip goes pin #11 and has a 14ohm resitance next to the next pin #12 going to pull that one, it's a 7427 which I don't have :( signals look sthe same, pulled chip and now mysterious signal on b4 is gone dont' have a new 7427 but pulled one off a donor board and replaced, gmae is OK! Explosions on attract screen anre NOT random, this is almost certainly a bad POKEYbad pokey, replaced with a used POKEY, Game is working correctly!!! OK! during LONG ram test board died, ram errors, not syncing to monitor, looks like VSYNC is messed up, incorrect values. 74LS08 @ D7 had a wierd VSYNC output, pulling, still same wierd signal D8 pin #2 seems to be connected to b4 pin #5?!? traced on end of D8 pin #2 to machine socketed chip @ D9 pin #1 - OK why is the flip signal going crazy? its flipping and it should not, ok maybe it should be its tied to reset, disabled watchdog now I have sync RAMS are getting 0xFFFF BTS errors, RAMs are recieving write signal, ROMS seem to be OK at least in range 0x5000 - 0x57FF watchdog writing is working replaced E2 and P5 to no avail. Board had previous work done on it, a few machined sockets in the areas I was looking at, pulled machined socketed pins and soldered in directly looking for something that can affect all rams, MADSEL... and MADSEL is not getting set, replaced R4 as 15 and 11 are dead... no change tested input #2 clock - OK, only thing left is LD pin #9 which is fed from pin #8 on E3 ! MADSEL is never going high, WHY?!? looking at flip from output circuit tried replacing F9 (273) no change it has to be something talking on the bus??? since D0-D4 affect MADSEL? but I'm pretty sure the BUS is good... argh Decided to go down the BUS rabbit hole... pulled all 244s on data bus no change :( getting 0x8a after write of 0x00 to any ram address getting 0xff after write of 0xFF to any ram address why is the ROMs buffer interferring with the RAM when in, but still have such wierd ram errors on write, multiple issues maybe? (hint, yes tehre were_ h6 tested bad pins 8 and 9, socketed and replaced, ram long test seems to be working now, RAMs test OK now ROMS are testing wrong!?! ROM at H1 should be f25a - NOT ROM at JK/1 reading 3977 - ok ROM at KL/1 should be e850 - reading 5893 ROM at LN/1 should be ef62 reading EFC2 Pulled H1 and rested the H1 Rnage (0x5000 - 0x57FF) I should not get ANYTHING, but I get the correct signature for the ROM at JK/1 ?$? checked JK1s enabled line it's ALWAYS enabled pull JK1 now H1, KL1 and LN1 are working! (which makes sense) eanbled pin on KJ1 is always high, this traces back to pin #3 on J6 output of J6 (08) does not match inputs, pulled and replaced j6 fixed that problem Game works!

Game Board #26 11/10/2016

Problem: Game does not work No video sync Troubleshooting/diagnosis steps: Tested watchdog, it is constantly resetting Tested CPU clock - OK Grounded watchdog, the video syncs and I get just a blue screen Did a Fluke 9010a RAM test for range 0x0000 - 0x3FFF - BTS FF @0x0000, which means the RAM is not working all bits reporting bad, at the first address tried. This is highly unlikely that ALL 8 RAMs went bad. So going to testsupporting hardware, especially the address decoding circuitry and the RAM write enable circuitry as that's often problematic First though I like to check all sync signals as they are needed throughout and often go bad ALl H outputs in SYNC including E7 !HBLANK - OK ALL V outputs in sync, chips A4, Br and #10 on !16V - OK So the SYNC circuits look good, check the address decoding circuits Address decoder @ N2 reseponds OK for a looping ram read @ 0x0000 OK Address decoder for the RAM range looks OK, let's look at the RAM input / output circuitry did a looping write @ 0x0000, checked pin #3 (!write enable) on rams, they are getting the signal. did a looping write @ 0x0000, I do seem to get data bits on pin #2 of all 2114 chips. p5 (Ram buffer, getting enable signal OK during looping read), all inputs are low (inputs are pins 2,4,6,8, 11,13,15,17,19) wrote 0x55 to 0x000 and did looping read, all inputs bits still low Validated inputs to RAMs they are getting the correct signals on the write..., but outputs of read are always high impediance/floating piggybacked a 2114 since all ram outputs seemed floating, 1 bit got better. Pulled that one RAM chip and replaced, now that bit is OK Pulled another RAM chip and replaced, that bit is OK replaced all RAMS, memory tests run OK.. odd that they ALL were bad! Board is now booting but trackball doesn't move left correctly AND the soudns is all messed up, staticy replaced the LM324 because that usually is the static problem - no change Tested with a known good POKEY, as that's the only thing left in the sound circuit - NO change. Put back original POKEY MC14584 @ C9 had already been socketed and replaced, tried a known good MC14584, no change Pulled 7474 @ J8 - no change, put a socket in and replaced original Issue must be on data bus, tried to track down issue, ended up replacing 2 74LS244s before I noticed that under the POKEY socket there seemed to be some damage Pulled pokey socket, saw some smashed traces, found one trace was cut. Repaired, replaced socket and re-inserted POKEY Sounds are OK and trackball moves correctly Game works!

Game Board #27 4/10/2016

Problem: Game does not work Game missing all EPROMS Game missing CPU Game missing POKEY Game missing bipolar PORM @ L6 Game missing 10Mhz crystal Troubleshooting/diagnosis steps: replaced missing 10Mhz crystal replaced missing PROM @ L6 still no clock on pin #37 of CPU no signal on 10Mhz test point tried another crystal, no change, put back first crystal pulled first chip to interact with 10Mhz crystal, 74H04 @ B6 didn't have a 74H04, used a 74LS04 had some noise on CPU clock switched to a 74S04, fixed that problem. now have clock and video sync doing RAM long @ 0x0000 - 0x3FFF - OK all socketed chips missing (CPU, ROMs, POKEY) - replaced game still not syncing checking ROMs in circuit h1 0x5000 - 0x57FF - f25A - ok jk1 0x5800 - 0x5Fff - 3977 - ok lk1 0x6000 - 0x67ff - cbe2 - ok ln1 0x6800 - 0x6FFF - ef62 - ok np1 0x7000 - 0x77ff - b25d - ok r1 0x7800 - 0x7fff - B888 - ok odd watch dog is still going off checking sync circuit D5 and E5 seem ok vertical syncs b4 and a4 seem fine getting both watchdog and no syncing (sync returns when watchdog is disabled) Tested some 74ls74s in circuit with HP logic comparator, last one I checked @ F7 was bad (7474) - replaced with 74LS74 game boots! thought screen to "big" might be LCD, adjusted out, looks good caps were pretty ugly replaced all 100uf @ 25v caps replaced all 10uf @ 25v caps replaced all 1uf 25V caps replaced 22uf 25V cap game boots and tests ok, but trackball doesn't move right or left replaced MC14584 @ C9 - fixed! Game works!

Game Board #28 4/16/2016

Problem: monitor is not syncing Game does not work Troubleshooting/diagnosis steps: Board is very clean noticed L6 is in backwards, put back now get junk on screen put in known good L6 Game boots but get ROM error 5 in test mode Tested the ROM in circuit, it is missile command v2 all rom ranges tested fine except ROM range 0x7000 - 0x77ff is bad just as the test mode indicated Found that ROM MN1/ and LM1 were swapped Swappd back found that ROM MN/1 was bad replaced test mode OK now! did a long fluke RAM test just to make sure RAM is solid - OK game works!

Game Board #29 8/20/2016
Problem: crosshairs is leavinga solid blue trail, blue bakcground over bases and arrows Troubleshooting/diagnosis steps: 74LS153 @ P7 tested bad, replaced Game works!

Game Board #30 10/15/2016

Problem: crosshairs is leavinga solid blue trail, blue bakcground over bases and arrows Troubleshooting/diagnosis steps: looks like someone replaced the socket on P7 which holds a 74LS153 That's a good diagnosis, and would be the first thing I tested. unfortunately the repair was questionable, not horrible mind you, but just not clean enough that I though it might be the issue, so I figured I'd pull it and make sure it was ok. ended up the repair was OK, but I cleaned it up and resoldered in a new socket anyway - no change swapped out the 74LS153 with a new one - no change Put back the original 74LS153 OK so the 74LS153 is one of the last chips in the circuit that usually causes this issue, so worked back to chips that influence the 74LS153, immediately saw a signetics chip (they seem to be 90% of the bad chips in my repair) at C5 (72LS00). Tested it, it tested bad in circuit. Removed the 74ls00 @ C5, it also tested bad out of circuit Installed a new 74LS00 @ C5 - fixed the video problem! Game works!

Game Board #31 3/31/2017

Problem: Static garbage on screen Troubleshooting/diagnosis steps: Weird stuff on screen Fluke bus test OK Boards ROMS have had jumpers modified Missing a few caps Some corrosion near CPU CPU clock ok RAM long 0x0000 -0x3FFF BTS err 0xff @ 0x0000, this means none of the RAM chips are working or there's an issue with the control circuit... often the socket @ l6 on the PROM that controls ram writes is an issue. Going to replace PROM socket @ L6 as it's original and that's often a problem Replaced ROM socket @ l6 Game works!

Game Board #32 4/7/2017

Problem: Static garbage on screen Troubleshooting/diagnosis steps: CPU clock ok Replacing prom socket @ L6, no change CPU bus test - data bit 0 - 7 tied high got to be the buffer Pulled 74ls244 @ e2, no change Could be B/C1 or N/P3 also or p5 or POKEY or M9 or P10, or L9 Pulled pokey not that Looked started probing enabled on the various 74ls244s above 74LS244 @ BC1 is ALWAYS active (on) when it should NOT be 74LS244 @ BC/1 is turned on by the 74H04 @ B6 pin #4, which is always LOW B6 pin #4 is controlled by the input pin #3 on B6 it is floating. B6 input pin is generated by the output of 7400 @ c5 pin #11. It is floating, it should NEVER be floating. The inputs to it (pin 12 and 13 are high), being a NAND gate, output pin #11 SHOULD be low when inputs are high, NOT floating. replaced 7400 @ C5 with 74S00, bus test passes. Replaced pulled 74LS244 @ e2 with pulled chip Fluke short RAM test 0x0000 -0x3fff - ok Fluke long RAM test 0x0000 - 0x3fff - ok Game works!

Game Board #33 4/26/2017

Problem: Blank yellow screen Troubleshooting/diagnosis steps: Tested CPU reset line, it is NOT resetting, which means either it's working (playing blind) or the watchdog circuit is not working. Tested CPU clock, - OK Fluke 9010A CPU bus OK Flude RAM long test 0x0000 - 0x3fff - ok H sync oK V sync is MISSING! Vertical counters A4 and B4 outputs look ok Lets go backwards on the vsync circuit, 7408 @ h7 output pin 8 - dead, input pin 9 ok, input pin 10 is dead (VBLANK) VBLANK is generated by 74S260 @ a5, verify output pin 5 is dead, it is Check inputs (12, 1, 2, 3, 13), inputs look ok, lets remove this chip, chip tested bad out of circuit Replaced, game now boots up fine Game works!

Game Board #34 5/20/2017

Problem: black screen will not sync Troubleshooting/diagnosis steps: Board is missing EPROM @ h1 Board has braze multi-missile command kit installed board set is Missile command version 2 Disabling the watchdog I get a green screen Remove Braze kit and EPROMS Fluke 9010 Bus test ok Ram long 0x0000 - 0x3FFF - ok Tested EPROMS, 1 missing, 1 bad. replaced h1 and jk1 with newly burned ones, no change, still reseting ROMS tested with Fluke in circuit, all OK Replacing POKEY socket as it fell off Tesetd pokey, OK Game still resetting, with reset signal Tried writing to loop at watchdog address - this DID NOT stop the watch dog reset signal - thats a problem E8 (7442) pin #5 controls watchdog reset, it tested bad in circuit and out of circuit, replaced, game works! game works!

Game Board #35 10/07/2017

Problem: black screen. Troubleshooting/diagnosis steps: Checked voltage - low but OK Checked Clock - OK Checked /RESET - it is watchdogging Fluke BUS test - OK Fluke RAM long 0x0000 - 0x3FFF - failed DCD bit 0 @ 0x0000 Removed POKEY and resetted RAM long - still same DCD bit 0 @ 0x0000 means that RAM address 0x0000 and 0x0001 should be "tied together, reading and writing to either will appear to affect the other with the same value Wrote 0 to 0x0000 - read back 0 - ok Read 0x0001 - was NOT 0 (something like 0xFD I think) Wrote 0xFF to 0x0001, read back OK Read back 0x0000 - now it's 0x01, that definitely doesn't look like a true DCD error write 0x00 to 0x0000, 0x0001, and 0x0002 Write 0xFF to 0x0002 Read back 0x0001 and 0x0002 both are now 0x01 write 0x00 to 0x0002, 0x0003 - read back to verify - OK wrote 0xFF to 0x0003 and verified Read 0x0002 - it read 0x01 - looks like data bit 0 is bad which really is a BTS error 0x01 Revmoed the RAM that corresponds to data bit 0 (4116 @ F4) Socked and replaced F4 Game works!

Game Board #36 11/18/2017

Problem: Game not working Troubleshooting/diagnosis steps: game does not work Voltage OK Clock OK Reset not stuck low Fluke Bus test - ok Fluke RAM long 0x0000 - 0x3FFF - failed BTS FF @ 0x1000 not likely to be an actual RAM error, more like an address decoding error dealing with address bit 12 when reading/writing to 0x1000 hit bit is correct on both sides of F2 /RAM at M3 pin #6 is incorrect Found 74LS42 @ n2 was bad Video of this fix at https://www.patreon.com/posts/15205858 game now passes RAM test and ROM test, and is not resetting, but all you can see is a yellow stripe at the bottom of the screen found bad 74LS04 @ k7, replaced Game works!

Game Board #37 05/01/2020
Problem: Game not working Troubleshooting/diagnosis steps: Voltage OK Clock OK Bus test OK RAM long 0x0000 - 0x3FFF - BTS error bit 0x08, that's 4116 @ K4, replaced Game works!