Looking For Repair Service

[Ponder]

Hi all.

Embarrassingly, while setting up a coin slot mechanism, I neglected to secure the coin counter wires and they touched my Bomb Jack PCB near the audio circuitry while inserting a coin.
The sound froze on a single note so I powered off and on again and now I have no audio at all. The game plays fine but silent.
I've been trying to diagnose the issue myself but having no luck. I know it's not the CPU because I've swapped the 2 over and the game still plays. Just no audio.
I've also rubbed the connectors near the amp chip and can hear the effect through the speakers.
I know the Supergun is ok because Choplifter still works perfectly, including all audio.#
Now I'm stuck and looking for more experienced help. Is there anywhere in the UK that repairs these without it costing an arm and a leg? I've got one quote from Square Eye at £120 + Parts + P&P, which I will pay if push comes to shove but I'm looking for somewhere more reasonable.
Can anyone suggest anything please?

 

[Alpha1]

I believe @sukhbir knows Bomb Jack but not sure if he repairs for other people.

 

[big10p]

Hopefully just something in the small audio amp section and easy to replace. Do you have a logic probe to check the sound CPU is working?

 

[Ponder]

I have a logic probe but can't figure out where the problem lies. It's a fresh sound CPU and I've swapped that for the game CPU which proves it's working. It was my first suspect to be honest but I quickly ruled that out.

 

[big10p]

One thing I need to get around to is make a simple audio probe. Useful in this situation. I just watched this video. https://share.google/NL0RuQuU7sKdh5ddj

 

[Retroman839]

I made phil mur probe its Awsome and fixed bomb Jack Áudio. Keep meaning to add a tiny laptop speaker to it.

Used it on Atari jaguar repair the other day also ..

Sukbir will I’m sure help you if you ask him
I’m suspecting your amp just on basis it’s right on front of pcb.. prone to lose wires.


You can put a multi meter on the amp ..
Continuity mode
Pin 1 to pin 2 short - amp is blown

 

[Ponder]

One thing I need to get around to is make a simple audio probe. Useful in this situation. I just watched this video. https://share.google/NL0RuQuU7sKdh5ddj

I do have a cheap oscilloscope in my Amazon basket. I intended to get one anyway but this is a little push.

 

[Ponder]

I made phil mur probe it’s Awsome and fixed bomb Jack Áudio

Sukbir will I’m sure help you if you ask him
I’m suspecting your amp just on basis it’s right on front of pcb.. prone to lose wires.


You can put a multi meter on the amp ..
Continuity mode
Pin 1 to pin 2 short - amp is blown

No short between pins 1 and 2. I'm in communication with Sukbir

 

[big10p]

I made phil mur probe its Awsome and fixed bomb Jack Áudio. Keep meaning to add a tiny laptop speaker to it.

Used it on Atari jaguar repair the other day also ..

Sukbir will I’m sure help you if you ask him
I’m suspecting your amp just on basis it’s right on front of pcb.. prone to lose wires.


You can put a multi meter on the amp ..
Continuity mode
Pin 1 to pin 2 short - amp is blown

Got a link to details of Phil's probe?

 

[Georgian2]

Do you hear any humm at all? If you slide you slide your finger on teh volume potentiometer do you hear anything at all? If is completly mute, most likely the amplifier is gone. If you hear anthing, something before the amlifier is gone.

 

[philmurr]

Got a link to details of Phil's probe?

Audio probe

I've been doing some work lately on some faulty sound boards and old drum machines, and found it quite tricky to work out exactly what part of a circuit was faulty. You can't really use a logic probe to help, and a 'scope can give difficult to understand readings. I had a look around for an...

www.ukvac.com

Bare pcbs are free, just need to pay postage

 

[Ponder]

Do you hear any humm at all? If you slide you slide your finger on teh volume potentiometer do you hear anything at all? If is completly mute, most likely the amplifier is gone. If you hear anthing, something before the amlifier is gone.

I rubbed the contacts on the underside of the amp and could hear as if I was rubbing the stylus of a record player.

 

[Georgian2]

I rubbed the contacts on the underside of the amp and could hear as if I was rubbing the stylus of a record player.

The amplifier should be OK. Something before it, is bad. most likely the opamp before it. Last page on the schematics. You need to check if there is anything on the LM324 inputs. If yes, LM324 is bad. But all 3 of them??
https://www.arcade-museum.com/manuals-videogames/B/bombjack-schematics.pdf

 

[Ponder]

The amplifier should be OK. Something before it, is bad. most likely the opamp before it. Last page on the schematics. You need to check if there is anything on the LM324 inputs. If yes, LM324 is bad. But all 3 of them??
https://www.arcade-museum.com/manuals-videogames/B/bombjack-schematics.pdf

There are M5224P Quad Amps on this board but they seem 100% equivalent. I'll check for signals when I get the oscilloscope. I'll have a quick check with the logic probe tomorrow.

 

[Georgian2]

There are M5224P Quad Amps on this board but they seem 100% equivalent. I'll check for signals when I get the oscilloscope. I'll have a quick check with the logic probe tomorrow.

An logic probe won't help you with audio signals. They are way to low. You can use desktop speakers or any kind of an audio amplifier to trace audio signals.

 

[Ponder]

An logic probe won't help you with audio signals. They are way to low. You can use desktop speakers or any kind of an audio amplifier to trace audio signals.

I didn't think so, thus the 'scope. I got a LOW on each of the connected input pins. The unconnected pins showed nothing on the probe.

 

[Georgian2]

I didn't think so, thus the 'scope. I got a LOW on each of the connected input pins. The unconnected pins showed nothing on the probe.

You are looking at mV range signals. For an logic probe, they are always LOW.

 

[Ponder]

Quick update: I have a cheap oscilloscope and have tested it for basic use and it should be what I need to test. All I now need is time! Hopefully over this long weekend. I'll update when I have done the testing.

 

[TheDaddy]

Good luck !

Dave.

 

[Ponder]

I failed to find anything useful. It appears that there is nothing coming from any of the AY chips.
Time to arrange the repair!