Whilst doing some testing for Guddler over on the UK-VAC forum I thought it would be a good time to look into why I sometimes get a POD timeout error.
Normally when I get this error pushing down on the black cable that connects it to the 9010 fixes it.
Here is the reason why
One of the crimps had worked its way loose.
I carefully bent the small bard out a little and refitted. Now the POD seems to be rock solid.
My friend Luca sent me this original Konami The Main Event PCB (a decent wrestling game):
After booted up game showed a clear sprite issue:
In these Konami boards sprites DATA are stored in 40 PIN 4Mbit MASK ROM so I went with my logic probe on the two ones @K4 and @H4 and found that the one ‘799B05’ @K4 has some DATA lines inactive.This was confirmed also by the MASK ROM test:
Reprogrammed the DATA into a 27C400 EPROM replacement gave me correct sprites:
Next issue to troubleshoot was the absolute lack of sound.Using my HP10529A logic comparator I found a 74LS74 @G5 with bad outputs but this was not enough to restore sound.Probing the audio Z80 CPU I found that all the control lines were silent so this convinced me to replace it (I had confirm it was really bad as I tried it in another board).At this point I had sound but only some speech samples randomly played.Analyzed the 2018 SRAM @F5 and found weird activity on DATA/ADDRESS lines.Desoldered and tested it confirmed it as bad:
Sound was finally fully restored.Last issue I had to solve was that some Player 1 inputs were not working, for example COIN 1 were stuck LOW as shown in TEST MODE:
As show in schematics inputs are handled by some 74LS253:
Probing the one @E12 with a logic comparator gave me problem on the two outputs, this was confirmed by out-of-circuit testing:
After replacing it TEST mode reported all the inputs working again:
So the board was 100% fixed.
Got this original Super Pang PCB from my friend ‘Mikidaffy1983’
He asked me to desuicide it (picture above is actually from the board already desuicided) and, as usual, I followed instruction here:
https://www.arcadecollecting.com/dead/pre-cps.html
All went good but when I tried the board I noticed wrong colors on some backgrounds/sprites:
Studying a bit the hardware I found that the color RAMs are located @8C and @9C (two 6116) so I started to analyze them with my logic probe, this revealed that some data lines of 6116 @8C were inactive.Desoldered and tested it out-of-circuit confirmed it was bad:
Fitted a good 6116 RAM brought colors to normal.
Bought this mint original Kaneko Air Buster PCB from my friend Corrado:
PCB was working fine but sound samples (drums, bass line, etc..) were played sometimes randomly other times in a bad way:
In this PCB (and a lot of other similar audio hardware) samples are played by the OKI MSM6296 chip which take DATA directly from the ROM that I dumped as good.Connecting an external AMP to pin 36 of the OKI6295 (this pin is the digital-to-analog converted signal fed into the UPC324 OP-AMP, you can download its datasheet here in the downloads section ) I had the same issue so this convinced me to replace the chip (with a rebadged one but it’s the same):
This restored fully music/FXs.Job done.
Another Rainbow Islands on the bench, this one from my friend “Mikidaffy1983”:
Board was in excellent state but when powered on all I got was a screen of wavy lines:
Started my usual visual inspection and didn’t notice nothing odd but when touched the PAL “B22-05” @IC33 I found it quite hot.Probing its outputs I found they were almost all dead so I programmed a GAL16V8 with the replacement hosted on this site (thank you Porchy and Macro for this).With the PAL replacement fitted the board succesfully booted but sometimes stuck on a static black/white striped screen , others times with bad/missing backgrounds:
Since I repaired other Rainbow Islands (and similar hardware like Bonze Adventure) I knew tiles are generated by the custom marked ‘PC080SN’ @IC34.This custom is connected to two 62256 SRAMs so I analized them with a logic probe and found that most DATA lines of the one @IC3 were stuck HIGH or LOW.Without thinking twice I desoldered and tested it having confirm it was bad:
Fitted a new 62256 SRAM led me to this point:
All backgounds/tiles were restored but there was a clear issue with the blue color.As we know RGB colors are generated by the custom module ‘TC0070RGB’ which on this PCB was resoldered but after a comparison with a good board I couldn’t find anything strange so I decided to move ahead and look into other issues.In particular there was no sound at all, only a buzzing noise sign that the main MB3735 amplifier was good.There was also no sound ouput from YM3012 DAC and this convinced me look into the digital part of the audio circuit.Probing the 6264 SRAM @IC44 revealed weird activity on its DATA/ADDRESS lines, testing it out-of-circuit confirmed it was bad:
Sound was fully restored but it was quiete and faint also at the highest volume.Connecting an external AMP to the inputs of the TL074 OP-AMP @IC67 gave me strong and steady volume so I rightly replaced this IC.
Back to the blue color issue I decided to go straight and remove the TC0070RGB module installing the Macro replacement resulting in a success.Board 100% fixed.
