Capacitor on game board pops after a Sanyo 20EZV recap and I lost audio

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I picked up a Donkey Kong machine in pretty good shape. The game played and there was audio, but the Sanyo 20EZV monitor could not be adjusted to something reasonable. The colors looked good, but the picture was constantly spiraling and there was no way to make it sit still.

So, I got a cap kit for it that included the audio board and recapped both the CRT and the audio board. The kit came with transistors for the audio board, but I did not replace those because the audio board was working fine before I didn't have any thermal paste on hand for the new transistors.

After the recap, I hooked the CRT up to a CraftyMech TPG and it looked way better and the spiraling motion had stopped, but the colors were inverted. I figured the inverted colors was just a signal mismatch between the CRT and the TPG and I decided to go ahead and put it back in the cab for an official full test.

However, when I powered the cab on, instead of the usual boot sound, a cap on the game PCB popped with a flash and started sizzling and smoking, so I killed the power.

Has anyone experienced anything like this before?
 
All connectors look fine and they even have labels on them to mark which is which. The bigger issue is that all my recap work seems to be for nothing as the monitor has returned to a never ending spiraling picture. So I didn't fix the CRT and now I have no audio.
 
you have it connected like this? you're aware the plugs have labels, so that's a start. but what you're describing sounds like they're going to the wrong spots.

sanyoamp.jpg
 
Later in the day, I pulled the little audio board out and inspected it closely for damage or caps that I might've screwed up during the recap. Everything looked fine, so I decided to go ahead replace the old transistors for the ones in the recap kit, just to make it a full rebuild.

After a few beers, I got brave... or stupid enough... to hook everything back up and try again. No fireworks this time and the audio is back! The CRT is still scrolling and spiraling like mad but at least the sound is back.

The capacitor that I think flashed and smoked is C13. I might be wrong because the flash was very brief and I can't really see any major damage other than a discolored spot near C13. Either way, I need to find out what was damaged and replace it.

I'm wondering if my original plan to NOT replace the old transistors was a mistake? Maybe mixing new caps with old, tired transistors is a bad ideal?
 
are you adjusting H. Hold on the monitor? there's also pots on the Donkey Kong video board, they stick out pretty far if the boards were out and can get smashed. if they're not then you'll need to adjust them.
 
I adjusted the pots on the top of the PCB stack and I didn't see any noticeable changes to the picture. Of course the picture is scrolling and spiraling so it's hard to see what's being changed. I saw a post that said these pots are for horizontal and vertical centering.

However, while plugging and unplugging the video cables during my switching from PCB video input to TPG input, I noticed that the picture would stabilize briefly when the plug is being pulled out, so it looks like my inspection and reflow efforts for cold solder joints missed something. I'll pull the CRT out this afternoon and look it over again. Fiddling with the cable and flexing the board in that corner has a huge effect on what the video image is doing.

A cold solder joint could explain why the CRT looked great on the bench but later looked terrible when installed in the cab. The weight of the TPG video cable may have been hanging at just the right angle to connect something up.
 
After fixing a cold solder joint at D208, which is right next to the pin connector for the video input, the monitor is back up and running solid. I put it back in the cab and my son and I played couple of 2 player games.

Now, as the machine got warmed up, some graphical artifacts started to manifest around text and ladders, but I will probably post that as a new issue.
 

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Just for note, the "graphical artifacts" around text and ladders was not due to any issues with the game board since my TPG showed the same, I just needed to adjust the bias pots on the CRT's neck board.
 

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I'm wondering if my original plan to NOT replace the old transistors was a mistake? Maybe mixing new caps with old, tired transistors is a bad ideal?
It's luck of the draw with them. I stock both audio board transistors because they are used on other stuff. Seldomly have I had them go bad. Certainly I don't think there is a problem with replacing them so long as you got them from a legit source. However, I don't think it is necessary. On an EZ20, usually a recap is good enough.
 
Just for note, the "graphical artifacts" around text and ladders was not due to any issues with the game board since my TPG showed the same, I just needed to adjust the bias pots on the CRT's neck board.
you should be doing this anyway
 
I finally had a moment to pull the CPU stack and inspect it. I initially thought it was a cap that popped, but it turns out to be a resistor just behind the suspected cap. If I'm reading it right, it's R13.r13_burn.jpeg
 
I finally had a moment to pull the CPU stack and inspect it. I initially thought it was a cap that popped, but it turns out to be a resistor just behind the suspected cap. If I'm reading it right, it's R13.View attachment 827800
Burnt resistors are a common failure when JB and JC are reversed on the EZ20 audio amp. It bothers me greatly that Nintendo didn't key those connectors or give one a different pin count.
 
Burnt resistors are a common failure when JB and JC are reversed on the EZ20 audio amp. It bothers me greatly that Nintendo didn't key those connectors or give one a different pin count.
I wonder how many game technicians back in the 80s executed that botch. lol

you should see the Zenith CD19MXRF06. there's a 3 pin header for negative sync, and then there's another 3 pin header that carries high voltage. I would argue that's significantly worse. +1 to @gamefixer for sharing that knowledge with me. if I'm not mistaken I think I had to cap one of those in Texas on a Mappy maybe?
 
I wonder how many game technicians back in the 80s executed that botch. lol

you should see the Zenith CD19MXRF06. there's a 3 pin header for negative sync, and then there's another 3 pin header that carries high voltage. I would argue that's significantly worse. +1 to @gamefixer for sharing that knowledge with me. if I'm not mistaken I think I had to cap one of those in Texas on a Mappy maybe?
Based on the fact that I've had several DK, DK Jr, Mario Bros, and Vs system boards come my way with burnt resistors (or in the case of Vs System, a blown out LM3900), I'd say switching JB and JC probably happened quite a bit. It's dumb, they really should have keyed it. Even techs make mistakes.

I've not heard about that with those Zenith monitors. I can't say I've ever serviced one, that sounds insanely dumb. I think Robbie Roto could have also have come with one of those crappy Zenith monitors as well. Midway has references to them in some of their manuals.
 
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