Solved Bubble Bobble Bootleg- No audio.

[Suteneko]

I'm going to be purchasing a bubble bobble bootleg that is missing it's audio amp and was wondering if anyone can confirm for certain my assumption that it uses a NEC 1181?

Picture of the bootleg board in question:


I believe @penrhos and @jengineer and perhaps a few other members on here have the same board, so I'd be extremely grateful if someone could provide a good quality photograph of the amp on their board or just the amps model number.

Thank you!

 

[qjuk]

Looks like I’ve got the same bootleg…


My AMP is a NEC 1182…


Hope this helps.

 

[Jacmar]

The NEC 1181 and 1182 are just mirrored versions of each other so either will work in your board , just ensure you get the orientation right .

And actually, looking at both of your pictures, there are holes for either amp allowing it to be screwed down flat to the board in the middle !

 

[Suteneko]

Thank you very much for the reply. I had assumed it would be a NEC 1181 or similar but just couldn't find a none blurry photograph to confirm my suspicion.

I'll go grab a 1182H!

 

[Martinmurphy30]

Seems kinda weird someone would rob a £5 amp off a fully working board though...... especially bubble bobble?

 

[qjuk]

They probably needed it to get another board working and didn’t have a spare to hand, or perhaps it was removed because it faulty and a previous owner didn’t get around to replacing it?

Thankfully the amps are still available and quite cheap to buy.

 

[Suteneko]

Seems kinda weird someone would rob a £5 amp off a fully working board though...... especially bubble bobble?

It's certainly not robbed. Looks like its been ripped off in storage. A bunch of the capacitors barely hanging on as well, one of which might require some minor trace/via repair.

But apart from that looking promising.

 

[Suteneko]

Well made some progress on this and finally re-populated the audio amp and replaced the half torn off capacitors.
Quite a few had damaged via's which thankfully weren't too hard to repair though I did have to resort to soldering 2 capacitors on the component side.



Wired up a Bubble Bobble to Jamma harness and it does boot fine:



However I have no sound. I have a buzz that increases or decreases when I adjust the volume pot but that is it at the moment.
All voltages are present including -5v so guess it's time to dive a bit deeper.

Any suggestions where to start would be great. Will set up my basic logic probe and start looking at activity in the area next time I have chance.

 

[Suteneko]

Looks like I've spotted a badly behaving 74LS374 while probing around the sound area.
Pulled the one above it as well to test but that one tests good out of circuit.
Don't have a spare so having to wait for the part to come in and fingers crossed that is the only problem.

 

[Suteneko]

Not much of an update but the replacement 74LS374's arrived today.
Sadly the same problem exists with no audio and just buzzing on the output, although I am getting better and normal looking behavior in that section and data is flowing through them now.

Sadly I am getting no output from the YM2203 pins 18,19 & 20 which should be the analog channels output to the amps and the TL074 has all stuck high pins apart from its ground pin.

Potentially faulty perhaps?

But then there is no audio coming out of pin 2 on the pair of ym3104 either and perhaps unlikely both the YM2203 and YM3526 are bad.
Maybe some more weird logic going on?

I did DIY a makeshift audio probe and cant find any audio output/input on the amps. Didn't really help me much as I already knew that.

Time to pull the 74LS155 and 74LS138 out of circuit to test to rule out any bad logic before suspecting anything bigger.

A job for tomorrow.

 

[Suteneko]

@qjuk would you mind confirming what pins on the connector edge are for Speaker + and Speaker - on your harness for Bubble Bobble?

I have Speaker + on 11 component side and Speaker - on the solder side at pin K.
Just want to rule out this is not something silly like those being wired the wrong way around.

 

[qjuk]

@qjuk would you mind confirming what pins on the connector edge are for Speaker + and Speaker - on your harness for Bubble Bobble?

I have Speaker + on 11 component side and Speaker - on the solder side at pin K.
Just want to rule out this is not something silly like those being wired the wrong way around.

Looks like you’ve got it wired up exactly the same as mine.

In the photo below, my black probe is pointing to the Speaker + pad on the parts side. The Speaker - is on the direct opposite pin (ie, pin K).



On a slight side note. I had a similar no audio issue with this same bootleg on a previous board I used to own. It turned out that one of the 74LS74’s in row L or M was faulty (IC9 and IC10 in your photo). Both of mine were Fujitsu’s so I replaced them both and it fixed the sound issue.

 

[Suteneko]

Thanks for that!
EDIT: Pulled both 74LS74 out of circuit and both are testing good.

The pair of 74LS374 are puzzling me as they should mirror each others outputs and everything looks good apart from PIN 19 and Pin 14 on IC25 which aren't apparently connected to anything.

According to the original Bubble Bobble schematics pin 19 on IC25 should connect to pin 18 on IC24 and Pin 14 on IC25 should connect to Pin 15 on IC24. But if I make those connections I get weird blue static noise artifacts in the video output.

I really thought maybe I had broke a via connection there but it appears that is normal for this bootleg?

IC24's 374 was faulty and has been replaced, but I feel I have been lead down a wrong rabbit hole.

 

[Suteneko]

This has been a right nightmare to diagnose and fix but finally got there.

Ended up de-soldering and putting in sockets for 20 IC in the audio Circuit.

Was it any of the 4 amps? ...of course not (well more on this later)
Was it the Sound CPU? ...Nope
Was it the Sound Ram? ...Nope
Was it the Sound ROM? ...Nope
Was it either of the two Yamaha Sound IC? Yeah, yet another dead end.

Was it any of the TTL 74LSxxx Logic chips in the sound circuit?
Nope as all of them test good out of circuit apart from that puzzling behavior of the mirror outputs of the two 74LS374.
I had to remove the socket i had put in to figure out what was going on and found that there was a broken trace between Pin 19 and Pin18 of the pair which I repaired. But the Pin 15 and Pin 14 connection was weird if connected. Well the simple matter was that its not connected at all on this bootlegs PCB by default, unlike on an original board. So I left it disconnected.

And this leads me to eventually going round all the board looking for broken traces in the sound section and finding nothing irregular.

Ages ago I had tested IC5, a 74LS240 that feeds the Sound CPU its 3mhz clock. I had only probed with my basic oscilloscope to ensure it had the correct frequency on its input and output pins which I did and thus I ruled it out.

However while scouring the schematic I noticed that Pin 3 of that 74LS240 is actually also connected to Pin 1 of a 74LS155 in the sound logic and low and behold its output looks strange... How did I miss this???

So assuming a bad IC I remove it to find it only blooming tests good as well...

But wait... I find a corroded trace underneath the IC..



Which I repaired and low and behold the sound comes back!

Albeit with very bad hissing in the Background Music so I replace the YM3014 at IC23 and its all sorted.

 

[Suteneko]

@qjuk I Don't suppose you could let me know what value capacitor is here? I'm missing it on mine.

 

[qjuk]

It’s a 25v 220uF.