Congo Bongo died, pcb brings 5v down

gwarble

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Hey all, where should I start looking, this original Congo Bongo pcb and power supply has always worked great... moved it the other day and now the game doesn't boot.

AC and other DC voltages seem fine, but with the pcb disconnected 5v is spot on, with its edge connector plugged back in 5v drops down to .3v

I can't see anything visually, and wiring doesn't seem to be the problem... but I don't really know what components to check first for shorts, seems to me it must be something on the PCB. I disconnected the molex between the two pcbs and it was still brought down, so maybe that narrows it down to the main pcb (or sound pcb, i didn't see its power connection)

Thanks, any tips appreciated
Joel
 
Might still be the power supply as it may look ok with nothing connected but unable to keep up with load. Power supply might be check using a load(either another pcb or a substitute such as a high power resistor.
If you have a multimeter, you can check the pcb by measuring ohmically between the ground and the 5vdc, 12vdc and -5vdc. It should be more than around 50 ohms.
If pcb at fault, the best way to find shorts is to inject a low voltage(1.5 to 2vdc) and check with a thermal camera what lits up. It could pretty much anything, mostly a cap or a chip.

Good luck
 
thanks guys

no test mode or booting at all without 5v

113ohms between 5v and gnd at the edge connector...

and good point i'll try to simulate a load to make sure the power supply isn't dropping when loaded (though -5v is powering the coin door and i think 12v or -12 is powering the sound board or amp enough to get a speaker pop when powering off

edit: from what i can tell -5 only goes to coin door, and -12 doesn't leave the power supply, so 12v must be making the speaker pop
 
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5vdc at 113 ohms looks good.
As it failed after the cab was moved, might be a wiring issue. Might want to check continuity between the edge connector and 5vdc power supply.
 
.2 or .3 ohms from power supply pcb to edge connector pins at pcb for 5v and gnd
That's good. Most likely in the power supply section. I guess still original power supply? Usually, a switching power supply will cut off the other powers when one of the voltage drops.
 
yeah seems good, edge connectors and pins look good... if 113ohms is ok between 5v and gnd on the board, then some active component might be shorting when powered on?

i'll rig up a light bulb or resistor load to test the ps

heat camera is a tool i don't have unfortunately

edit: yes original g80 power supply
 
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yeah seems good, edge connectors and pins look good... if 113ohms is ok between 5v and gnd on the board, then some active component might be shorting when powered on?

i'll rig up a light bulb or resistor load to test the ps

heat camera is a tool i don't have unfortunately
I doubt it. It might short after a while when heating up but to have the ps to go to .3vdc right away. Very slim chance.
I don't know if you have any 5/10 or 25 watts resistors, around 50-100 ohms, if not, would need something that could draw a little current such as 2+ amps. Bulb might do if ps unable to take any load.
 
great, thanks for the help, i'll focus on finding something to put a load and see if it will bring down the ps... will try after lunch

if it does, then i guess cap the power supply or check the heatsink mounted transistors?

edit: oh yeah like you said, something from moving it i'll double check all the wiring for something loose... i didn't disconnect the ribbon cables between all the pcbs maybe i should (didn't want to touch them)
 
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Not sure what board is in the cab. Most likely the power transistor such as 2n3055 would be at fault. I doubt it would be a cap.
Let us know how it goes.
 
You can try an 1158 automotive bulb. It's a 6v dual Filament bulb that has 17/5W filaments. The 17W should draw about 3 amps.

Also, like I'd said in our PM convo the other night about the other game... don't forget to check connections on your PS fuses for poor connections. Also, connectors from the PS to the game board too.

Does it still have the OG linear supply, or has it been bumped to a switcher?

Dylan
 
TO-220's seem to be the power transistors on the heat sinks if i'm reading the manual right, when i get back home i'll look

fuses, connectors, wiring all checked out at the beginning, only problem found is the 5v drops with the pcb connected and not when not
 
Could be a shorted ttl chip on the pcb or shorted cpu etc. Could also be the power supply failing under load, hard to say without seeing the game. Have no idea about congo bongo but looks cool
 
I've had a number of Sega original switching power supplies go bad just as you describe. Replacing with another will probably fix your game. There is usually a switching power supply for the +5v, and another board for the +12v. You can rewire to make it all come from a new PS, or just use the new PS for +5v. I'm pretty sure it's the power supply and not the pcb board.
 
Disconnect the pcb and measure resistance on the pcb edge connector between 5V and GND. If it is a few ohms (1-3 or so), the short is on the pcb.

While the pcb is disconnected, measure resistance at the edge connector of the harness, between 5V and GND.

p
 
sure i could swap in a switcher or even a wall wart for just the 5v, and may as a test, but I'd rather find the culprit and fix the original power supply if possible, hence this thread

one of the input AC voltages into the power supply is a little toasted, not bad but surely adding some resistance so I might repin that.
edge connector harness pins .2ohm between 5v and gnd


edit: dangit, thanks parism I must have mismeasured before, checked again and between 5v and gnd on the board edge connector while disconnected is 93ohms, double checked and now its back to sounding like a short on the board with that resistance...

edit: i don't know, now its been off a little longer and i'm reading 58ohms between 5v and gnd... still high but a lot different than 93
 
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ok i don't get it, thinking that polarity checking a resistor doesn't matter, I wasn't paying attention before, but now if I check resistance between 5v and GND edge traces on the pcb, I get 93ohms one way and if I swap the leads I get 58ohms... so some diodes in the circuit are affecting that reading but either way it is too high right? This is pins 1&2=GND and 3&4=5v on the top side of the cpu pcb

as journeymandt pointed out above, I'm having a similar issue with my asteroids deluxe, and just now checked and have 276ohms on that pcb one way and 242ohms the other way, interesting

edit: low! not high... will look with fresh eyes tomorrow
 
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ok i don't get it, thinking that polarity checking a resistor doesn't matter, I wasn't paying attention before, but now if I check resistance between 5v and GND edge traces on the pcb, I get 93ohms one way and if I swap the leads I get 58ohms... so some diodes in the circuit are affecting that reading but either way it is too high right? This is pins 1&2=GND and 3&4=5v on the top side of the cpu pcb

as journeymandt pointed out above, I'm having a similar issue with my asteroids deluxe, and just now checked and have 276ohms on that pcb one way and 242ohms the other way, interesting

edit: low! not high... will look with fresh eyes tomorrow
You are reading too much into the meter measurements on the inputs to the board(both games) at this point in time.

This is for both games... if all your connections are good, and your +5v is reading good without the game pcb connected(you did wiggle the wires to discount compromised crimps at the pins right?) You want to determine if it's a pcb issue, or a power supply issue first.

Check the power supply(both machines) by loading the supply with a different load. go to the auto parts store and buy a 6v bulb and a pigtail socket.(I think I mentioned an 1158 bulb before, but I'm too lazy to look back).... setup the bulb and socket with alligator clips... a 17W bulb should draw about 3 amps(math says 3.4A at 5V with a 17W bulb). With the pcb disconnected, clip the leads from the bulb to the ground and +5v leads/wires/test points, whatever... and measure the output with your multimeter.

If the voltage sags(you don't get around 5V) then your PS is the issue.

Alternatively, if you feed the pcb with 5v from a known good supply(hot and ground to their respective places) and the voltage sags, or pops a fuse... then you know it's a pcb issue....

Pcb issue means you start by checking bypass caps for shorts, and give a side eye to tantalums... they often fail shorted which can sag a good power supply.

Also of note.... if your +/- 12V rails on a Switcher are shorted, it will cause the Switcher to shut down... which of course will drop your 5v too... in other words with a switcher, it is possible the problem can be on the +/-12v side(usually audio) and not the 5v side.

That's why I asked if you had the OG supply, or if it had been replaced with a switcher... the OG supply has a transformer that feeds 2 switching "modules"... one for +/-12V, and 1 for 5V... the OG setup shouldn't shut down the 5V side if the 12V side is shorted, but a switching supply that feeds both could.

Obviously the other game differs in that it doesn't have a switcher... but, loading the supply with the pcb disconnected will reveal to you to a board problem, or a power supply problem.

You need to determine which side of the 5V is the problem to know what to look at next

Good luck
Dylan
 
You are reading too much into the meter measurements on the inputs to the board(both games) at this point in time.

This is for both games... if all your connections are good, and your +5v is reading good without the game pcb connected(you did wiggle the wires to discount compromised crimps at the pins right?) You want to determine if it's a pcb issue, or a power supply issue first.

Check the power supply(both machines) by loading the supply with a different load. go to the auto parts store and buy a 6v bulb and a pigtail socket.(I think I mentioned an 1158 bulb before, but I'm too lazy to look back).... setup the bulb and socket with alligator clips... a 17W bulb should draw about 3 amps(math says 3.4A at 5V with a 17W bulb). With the pcb disconnected, clip the leads from the bulb to the ground and +5v leads/wires/test points, whatever... and measure the output with your multimeter.

If the voltage sags(you don't get around 5V) then your PS is the issue.

Alternatively, if you feed the pcb with 5v from a known good supply(hot and ground to their respective places) and the voltage sags, or pops a fuse... then you know it's a pcb issue....

Pcb issue means you start by checking bypass caps for shorts, and give a side eye to tantalums... they often fail shorted which can sag a good power supply.

Also of note.... if your +/- 12V rails on a Switcher are shorted, it will cause the Switcher to shut down... which of course will drop your 5v too... in other words with a switcher, it is possible the problem can be on the +/-12v side(usually audio) and not the 5v side.

That's why I asked if you had the OG supply, or if it had been replaced with a switcher... the OG supply has a transformer that feeds 2 switching "modules"... one for +/-12V, and 1 for 5V... the OG setup shouldn't shut down the 5V side if the 12V side is shorted, but a switching supply that feeds both could.

Obviously the other game differs in that it doesn't have a switcher... but, loading the supply with the pcb disconnected will reveal to you to a board problem, or a power supply problem.

You need to determine which side of the 5V is the problem to know what to look at next

Good luck
Dylan
you know what's crazy is the [working] Zaxxon at work is still running the original power supply and the caps tested better than new Nichicons so I just left it in there as is. I recapped the whole sound section and did the weird resistor mods to make the new caps caca like the original ones to make all the sound lines work properly.

I think there's too much resistance between +5V and ground to signify there being anything amiss at the game board. in my very very early jedi training it was suggested that +12V can fail on switching mode power supplies, because that circuitry is just a byproduct of +5V load (hence the need for the load and the "switching" aspect of SMPS)... the power supply could have just given up the ghost. I've swapped a Happ PowerPro in that Zaxxon but decided after the fact that there was nothing wrong with the original one so I'll use that. the holes where you screw it in will be the only real difference, and pay attention to where you're taking the wires from. Sega colors are different, yellow is +5V, red is +12V, and white is ground usually... I can't visualize Zaxxon's wiring now. that was thousands of missions ago.
 
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