Omega Race - CAP >BOOOM!<

[FrizzleFried]

OK... I took a look at the board... I followed the trace from the capacitor to a bank of 4 diodes. They are the glass type. The schematics describe them as IN4004 whatever that is. The first one... broken. I didn't even need to test... when I desoldered one end it became obvious it was broke. Now, it's the top diode so it could have been broken in the explosion the first time through... but would it cause the explosion the 2nd time?? I also tested the one below which measured .737 one direction and nothing the other ...which I assume is ok. I happen to have a few diodes around but the closes I could find measured .775... probably too far off. I could yank one from my parts board though.

What are the chances that diode is the culprit? Do diodes just go bad (causing the first explosion)?

 

[smalltownguy2]

OK... I took a look at the board... I followed the trace from the capacitor to a bank of 4 diodes. They are the glass type. The schematics describe them as IN4004 whatever that is. The first one... broken. I didn't even need to test... when I desoldered one end it became obvious it was broke. Now, it's the top diode so it could have been broken in the explosion the first time through... but would it cause the explosion the 2nd time?? I also tested the one below which measured .737 one direction and nothing the other ...which I assume is ok. I happen to have a few diodes around but the closes I could find measured .775... probably too far off. I could yank one from my parts board though.

What are the chances that diode is the culprit? Do diodes just go bad (causing the first explosion)?

If the diode is leaking AC, then yes, fireworks.

 

[FrizzleFried]

If the diode is leaking AC, then yes, fireworks.

I don't know if it was "leaking" anything... it was physically broken.

I did find a couple suitable caps (50v rather than 35v) so I can try... but can anyone make any other suggestions on where to look? I'm not so concerned with the caps as I am with the smell over and over... and of course the possibility I'm damaging other components of course.

 

[ifkz]

This makes me wish someone would create an Omega Race linear power board rebuild kit. With luck Omegaman will see this thread and offer some suggestions. I know my board could use a rebuild too.

Friz, here is what they meant by leaky:
http://forums.arcade-museum.com/showpost.php?p=1738171&postcount=4

 

[Womble]

I don't know if it was "leaking" anything... it was physically broken.

Quite possibly a dead short until it fell apart, that would let the reverse AC component through which would be the wrong polarity for the electrolyitic - this makes them go kabooom!

 

[FrizzleFried]

OK... tested all 4 diodes and 2 were bad. Replaced both. Noticed a bad trade under one of the diodes. Repaired trace. All 4 diodes are now reading similar to what my 99.999% parts board reads so that is good.

Unfortunately when I fire up, I am still getting crazy vectors at the middle top right... though they do appear to be more a diagonal line than before. I power down as soon as I see the incorrect image so as to not blow the capacitor, etc.

I double check the diodes and they all appear fine.

Not sure where to go from here. The broken trace leads to a transistor... can that be tested on board? >sigh<

I got a local friend who may be able to help me.

 

[channelmanic]

Transistors typically short out when they go bad, just like a diode.

However, they can become leaky which makes it tough sometimes to troubleshoot them.

What is that voltage source used for? You may have some screwed up chips because of the negative voltage swing from the AC that was flowing through the board.

RJ

 

[demogo]

OK... I took a look at the board... I followed the trace from the capacitor to a bank of 4 diodes. They are the glass type. The schematics describe them as IN4004 whatever that is. The first one... broken. I didn't even need to test... when I desoldered one end it became obvious it was broke. Now, it's the top diode so it could have been broken in the explosion the first time through... but would it cause the explosion the 2nd time?? I also tested the one below which measured .737 one direction and nothing the other ...which I assume is ok. I happen to have a few diodes around but the closes I could find measured .775... probably too far off. I could yank one from my parts board though.

What are the chances that diode is the culprit? Do diodes just go bad (causing the first explosion)?

Are 1N4004 diodes really "glass types"?

 

[FrizzleFried]

Transistors typically short out when they go bad, just like a diode.

However, they can become leaky which makes it tough sometimes to troubleshoot them.

What is that voltage source used for? You may have some screwed up chips because of the negative voltage swing from the AC that was flowing through the board.

RJ

I have no idea... I am GUESSING here but I'd say this was something in the vector circuit. I say this because with the cap removed the board still flashes the start buttons as normal.

I am pretty much a newb when it comes to anything more than a simple cap kit, etc...

 

[FrizzleFried]

This appears to be the "area" that I am having issues. C106 is the cap that keeps blowing. D111, D112, D113, and D114 are the diodes checked. D112 and D111 were bad...

 

[kstillin]

Double check the polarity next time.
Notice that on this side of the circuit (with the 7915), the + leg goes to GROUND. On the other side, with the 78xx regulators, the - leg goes to ground.

There isn't much to this piece of the circuit- a few diodes to form a bridge rectifier, some smoothing caps (C106,C113) and then one negative and three positive voltage regulators.

You can do this.

 

[FrizzleFried]

Double check the polarity next time.
Notice that on this side of the circuit (with the 7915), the + leg goes to GROUND. On the other side, with the 78xx regulators, the - leg goes to ground.

There isn't much to this piece of the circuit- a few diodes to form a bridge rectifier, some smoothing caps (C106,C113) and then one negative and three positive voltage regulators.

You can do this.

Yes... polarity was correct... I double/triple checked before I powered up.

...both with the manual AND the extra parts boardset I have sitting here.

Is the issue perhaps with the transistors? Voltage regulators? How do I check these parts out. I am 100% sure I put the caps in correctly.

 

[FrizzleFried]

BTW - Any locals have Omega Race they'd be willing to let me drop my PCB set in to to eliminate a PS/harness issue for sure?

 

[channelmanic]

OK...

You've replace a couple of diodes... which ones?

If they are both of the diodes that feed into C106 and U101 then replace C106 and U101 as it's probably damaged too.

U101 can be had at Mouser. I have a slew of 'em here at the house too.

Once you get the PS fixed and the outputs proper then you can say for sure that your board has been damaged too.

RJ

 

[FrizzleFried]

OK...

You've replace a couple of diodes... which ones?

If they are both of the diodes that feed into C106 and U101 then replace C106 and U101 as it's probably damaged too.

U101 can be had at Mouser. I have a slew of 'em here at the house too.

Once you get the PS fixed and the outputs proper then you can say for sure that your board has been damaged too.

RJ

D111 and D112 were replaced. I can pull U101 off my parts PCB I imagine?

As for the PS, I measure 4.95v at at chip... same as it was before the issues started?

 

[FrizzleFried]

Well, U101 was bad... replaced it with U101 from the parts board. Put another cap at C106 just in case (the last time it didn't blow but I did power down as soon as I saw the image was jacked)... plugged her in and...

SAME...



Looking at the two boardsets I have... one uses a bunch of what looks like tiny diodes but are listed as "CP" ...a tiny capacitor... on the schematics. An example is CP237 on the above schematic graphic... though it's actually CP327 not CP237... but I digress. In any case, on the "used to be working" PCB set, that is a resistor?! Same with a ton of other ones next to the chips... on the parts board I have they are all tiny diode looking things but on the what was working board they are all tiny resistors.

Unfortunately their resistance don't match at all... so I can't "compare" them.

An example is that CP237/327... it is part of the circuit that is blowing... the diode (D109) is testing good... but the resistor that is in there measures 9.00 when set at 2K... when I check out the parts board, the same spot has that CP thing... and it measures 20 on the 20K setting?! I am guessing I am reading those CP's wrong or something?

I dunno... I am at my wits end right about now. I sure wish I knew WTF I was doing.

 

[CrazyKongFan]

Man, sorry about your troubles, but I gotta say, I like your new avatar...seems fitting

 

[FrizzleFried]

Yeah... exactly.

Looking at the PS schematics, etc... it looks like the circuit I'm having issues with is the 18v circuit... from what I can see though, that comes directly from the transformer and not through the linear power supply... am I seeing that right?

 

[G-P-E]

Are 1N4004 diodes really "glass types"?

Some of the old ones were... haven't seen a glass one in eons.

For the cost of a 1N4004 at about a nickel apiece - I would replace the whole set of four.

Ed

 

[demogo]

Some of the old ones were... haven't seen a glass one in eons.

For the cost of a 1N4004 at about a nickel apiece - I would replace the whole set of four.

Ed

Ah. I had some 1N4007s sitting here that are definitely not the glass types and I thought it odd that there'd be multiple types with the same number...