Meant to post this on Monday before the video went to the general public
Mammouth Missile Command PCB repair.
Andy acquired a Missile Command cocktail table last year which was known to have a board fault. Feeling confident after getting my own working I thought i'd take a look at this.
[tube]o55TV4ZwEfk[/tube]
This repair was about 14 work hours spread over nearly 3 weeks.
All I had to go off was it wasn't booting up - just a flickering yellow screen:
Board is using all 2716's.
Found a faulty ROM at H1 (035820-02)
Socket and replace failed 7442 at 2N (14 pin) as none of the /PROGSELx lines were working properly to their 139 decoders.
Someone had tried to replace a 7442 at 8E with a breadboard with a 138 on it - it wasn't working even though the 138 tests good so I replaced it with a proper 42 - don't know who thought that one up but the breadboard wasn't holding in place anyway so it wasn't the best idea.
Can talk to ROM now but RAM is failing with stuck bits (01000100) - socket remaining RAMs and replace the two problem ones (put one in backwards by accident as it was 2am). Replaced all 8 x 4116 anyway from some stock Andy had - most were good but it would have resulted in mis-matched RAM which can cause issues and red-herrings even when the RAM test reads ok.
Game boots up now but i've got garbage where the yellow area should be (last 32 lines of the screen).
Some head scratching went on but eventually I found I had a bad LD3COL signal which originates at the S32 at C3 so that was replaced and now i've got the cities area working.
I've now got all the blue writing coming out purple or multi-coloured once the board warms up - eventually this degraded into being permanent. Some major tracing around the circuit as I wasn't sure what was going on but I suspected both the PROM at L6 and the colour RAM at L7.
Board starts going out of vertical sync and then dies again - lack of VSYNC signal on the test point, HSYNC is fine, traced back to a bad LS260 at 5A - one of the few parts I don't have. Borrowed one from another board i'm working on and its back alive again.
Probing around I found what I thought was a bad signal coming out of the S32 at 5L - one input was active low, the other active high so I thought the output wasn't quite right, but the logic comparator said it was fine (I had a line in the middle of the screen and everything went up or down from this). Took a gut chance here and pulled the 32 and tested it out of circuit and it was definitely bad, replaced and all the text and everything is solid now.
I ended up replacing the PROM at 6L as when it warmed up it was generating streaks all over the place. Replaced and its fine. I had Mark from Retroclinic burn me a couple as I was in doubt on whether this was the problem with the badly coloured text and missile lines.
Finally as the board kept being intermittent every time i'd flipped it over to solder something and back I replaced the 40pin sockets on the POKEY and CPU
Sound not working - inject the AUD1/AUD2 with my pulser and the speakers work, trace way back and find the LM324N at N10 is dead.
Soak testes on the bench for 6 hours with no faults developing, put it in my lovely MC cab and played it a bit and its solid.
I also fixed the intermitted boot problem on my own board as well which was a failing 2716 @ L/K1 (ROM4) and some bad solder around the 139 @ P2 - boots up fine now every time.
The video shows all the weird signals and my workings out. Its just over an hour long and for the interested definitely worth a watch and a good laugh - there's probably some points where you'll want to shout at the screen at me.
Mammouth Missile Command PCB repair.
Andy acquired a Missile Command cocktail table last year which was known to have a board fault. Feeling confident after getting my own working I thought i'd take a look at this.
[tube]o55TV4ZwEfk[/tube]
This repair was about 14 work hours spread over nearly 3 weeks.
All I had to go off was it wasn't booting up - just a flickering yellow screen:
Board is using all 2716's.
Found a faulty ROM at H1 (035820-02)
Socket and replace failed 7442 at 2N (14 pin) as none of the /PROGSELx lines were working properly to their 139 decoders.
Someone had tried to replace a 7442 at 8E with a breadboard with a 138 on it - it wasn't working even though the 138 tests good so I replaced it with a proper 42 - don't know who thought that one up but the breadboard wasn't holding in place anyway so it wasn't the best idea.
Can talk to ROM now but RAM is failing with stuck bits (01000100) - socket remaining RAMs and replace the two problem ones (put one in backwards by accident as it was 2am). Replaced all 8 x 4116 anyway from some stock Andy had - most were good but it would have resulted in mis-matched RAM which can cause issues and red-herrings even when the RAM test reads ok.
Game boots up now but i've got garbage where the yellow area should be (last 32 lines of the screen).
Some head scratching went on but eventually I found I had a bad LD3COL signal which originates at the S32 at C3 so that was replaced and now i've got the cities area working.
I've now got all the blue writing coming out purple or multi-coloured once the board warms up - eventually this degraded into being permanent. Some major tracing around the circuit as I wasn't sure what was going on but I suspected both the PROM at L6 and the colour RAM at L7.
Board starts going out of vertical sync and then dies again - lack of VSYNC signal on the test point, HSYNC is fine, traced back to a bad LS260 at 5A - one of the few parts I don't have. Borrowed one from another board i'm working on and its back alive again.
Probing around I found what I thought was a bad signal coming out of the S32 at 5L - one input was active low, the other active high so I thought the output wasn't quite right, but the logic comparator said it was fine (I had a line in the middle of the screen and everything went up or down from this). Took a gut chance here and pulled the 32 and tested it out of circuit and it was definitely bad, replaced and all the text and everything is solid now.
I ended up replacing the PROM at 6L as when it warmed up it was generating streaks all over the place. Replaced and its fine. I had Mark from Retroclinic burn me a couple as I was in doubt on whether this was the problem with the badly coloured text and missile lines.
Finally as the board kept being intermittent every time i'd flipped it over to solder something and back I replaced the 40pin sockets on the POKEY and CPU
Sound not working - inject the AUD1/AUD2 with my pulser and the speakers work, trace way back and find the LM324N at N10 is dead.
Soak testes on the bench for 6 hours with no faults developing, put it in my lovely MC cab and played it a bit and its solid.
I also fixed the intermitted boot problem on my own board as well which was a failing 2716 @ L/K1 (ROM4) and some bad solder around the 139 @ P2 - boots up fine now every time.
The video shows all the weird signals and my workings out. Its just over an hour long and for the interested definitely worth a watch and a good laugh - there's probably some points where you'll want to shout at the screen at me.
