Gorf Power Board Repair - Opinions Needed...

Alan173

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Discovered today my Gorf was blowing the 2amp slow blow fuse in my game. Isolated it down to the 11 pin connector on my power board. Interesting enough all voltages on this board just checked fine a month ago....so something just gave up the ghost. I checked the 4 diodes of pins 3-4 and 5-6 (IN4004's) out of circuit and they checked fine. I then noticed one of the capacitors seems to have a burst in it's end. A reason to cause a short and blow the 2 amp fuse? Well....I went through my photo's from a month ago and it shows the same condition on the capacitor and the game was not blowing a fuse then.

Hmmmmm......lust looking for some opinions before I tear into it...maybe there is a common failure point/short for these boards somebody can share.

BTW.....power board is A082-90411-B000.
 

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Alan, you need to change all of the caps at the same time. The headers will need to be replaced sometimes too as they get burnt.
 
Hi Dave!

Well.......a bit of a different approach here (I can explain later). This board is pristine.....and I need to isolate the failure....or at least that is what I would like to do. Header pins are perfect....but there is a dead short somewhere. I guess I can start checking ALL the diodes...that is an option. I know the one cap in question is tough to buy at a reasonable price and I'm not sure if there is a get well kit for this old Midway board out there...
 
I did the Bob Kit. Yeah, it's 20 something $, but...if you plan on keeping this game, do the kit and fix it right. It upgrades the diodes, replaces all the caps and the pots I believe. I think it will outlast a new switcher. I also recommend new header strips on the PCB (Bob has these) and re-pin the connectors.
 
I know the one cap in question is tough to buy at a reasonable price and I'm not sure if there is a get well kit for this old Midway board out there...

Hi Alan,
If that cap isn't gone yet....it's on it's way. It's almost impossible to find a 2000uf cap.....but a 2200uf works like a charm (and easy to find). If you want to go real cheap...you could zip-tie a radial instead of an axial....$2-$3 maybe.

I just checked Mouser: radial = $.83.......axial = $1.98.

With that said...I don't think that cap is the problem (though, I agree, it needs replacing). That cap is in the -5VDC line...your 2amp fuse is for the audio voltage. Check the four diodes at the negative end of the 4700uf cap...and the one diode by the positive end of the same cap. Also try unplugging the audio amp/volumn board. If the issue isn't one of those five diodes....it's the audio amp board.

Good luck,
Edward
 
Hmmmmm......lust looking for some opinions before I tear into it...maybe there is a common failure point/short for these boards somebody can share.

BTW.....power board is A082-90411-B000.

Just throw an ATX power supply in there with an adapter, and be done with it... those supplies are terrible.
 
Yeah....I know. I'm just gonna give this one a little extra love and see what I get in return.

So.....all the diodes on the power board check out just fine. I see on the power supply schematic exactly what Edward is saying....the 2 amp fuse is in line with the audio circuit. And guess what......when the fuse blew I lost all sound. so now I disconnected the audio amp board and plugged in the power board......no fuse blow!

So it is on to the audio amp board for analysis....

Stay tuned...

Alan
 
Both amps checked fine (Q1 & Q2).....and both on-board transistors (Q3 & Q4) checked fine. That cap on-board reads continuity both ways.......darn it. I don't have one of those in my parts box. By the way......that is a weird cap.......any suggestions where to pick one up? I think we have found our culprit.....;-)....
 
TRouble finding cap....

It seems the Kemet T310 series 15uf 20VDC is obsolete? Either that or very hard to find. I found some on e-bay but you have to buy 25 for 20 bucks. Any better options out there or equivalent replacements capacitors for this swap? Mouser has some that are close...
 
It seems the Kemet T310 series 15uf 20VDC is obsolete? Either that or very hard to find. I found some on e-bay but you have to buy 25 for 20 bucks. Any better options out there or equivalent replacements capacitors for this swap? Mouser has some that are close...

Throw on something common like a 22uf 25v then...
15uf is an odd value... 20v is an odd rating...
 
It seems the Kemet T310 series 15uf 20VDC is obsolete? Either that or very hard to find. I found some on e-bay but you have to buy 25 for 20 bucks. Any better options out there or equivalent replacements capacitors for this swap? Mouser has some that are close...

For axial style - use Kemet T322D156K020AS or T322D156K020AT
For radial (dipped) style - use Kemet T350F156K020AS or T350F156K020AT

-- Ed
 
Thanks Ed!

I knew it was between the T110 or the T322 series. Looks like a Mouser order is in the works......geeeeesh......didn't I just get one last week?! The never ending saga of keeping the classics rolling. Once I get it replaced I'll give an update as to what I'll be working on next.....maybe playing some Gorf??? ;)

Alan
 
Blown Tantalum Cap.....

For those interested here is a picture of the blown tantalum cap. Notice the hole blown outwards in the pictures below. On board it read as a dead short and removed it read as a dead short. Resistance read approximately a steady 5ohms when removed....
 

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