Got a Project Kiss machine. I have it all up and running now except for sound.

Worked on the sound card all day today. Have made progress but not fixed.

Originally had no sound at all. I replaced U3 U4 & U5 as all 3 faulty!! That got me sound with varying tones etc. Sustain adjustment works but the volume is low. I can adjust the volume but on max it is still low.

Also replaced the multiple 1uf and the 2.2uf caps.

Cleaned and tested the two Pot's.

So I replaced U9 with a UA741CN and it made no difference...
So I replaced the LM380N and if aything it got a bit worse so put the original back in...

I read somewhere that U9 Pin2 should be around 2vdc - but mine is 6vdc - what would cause that???

Any other suggestions?

It's only C13 on the output but that measures good.

Bump...

All the signals from U11 are spot on with the scope.

It's definitely and amp issue.

If I take U9 out of its socket I measure 0v on pin 2 and 6v with the IC in. Is that correct?

I have tried a few UA741's and no difference....

Does anyone have any measurements for the inputs and output of the 741 & 380 ?

Yes this one has the load resistors:

I have 5x LM380N in stock but when I put them in I lose all sound and the heatsink on the 12v starts getting hot. So I reckon they are Chinese duds. Luckily the original 380N I think is ok as when measuring the inputs on the scope the output is much stronger looking so it looks like it's amping.

The 471 though - I get 6.4v on pin 2,3 & 6 and the audio signal is basically unrecognisable at all.
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The 741 - inputs & output is 6.4vdc

The 380 - The output is 6.4 vdc - BUT the inputs are 0.4vdc ??

I get 3.6vdc on the pot side of C9 (or whatever I adjust the pot to). The other side is 0.4vdc or basically ground..

lm380 Not on pin 2 but on pin 6 when measuring with the scope the speaker goes crazy distortion

The LM380 pin 6 goes wild

Readings are very low so jumping about but 741 / 6 is between 10mv ac to about 50mv ac ----- and the input on the 380 is about 20mv ac to 30mv ac ---- so similar

I changed C9 also and no fifference

Do the UA741 work on these boards?

I read a comment somewhere that they do but now I'm not so sure...

Mine looks like a knock off of yours...

China knocking off it's own knock offs...lol

I reckon it has to be the 741. If I short U8 the volume increases a little but nothing much.

Tone adjustment works so that whole part of the input circuits to the 741 look to be working. The power amp 380 does show a much larger output compared to it's input (albeit very low input).

Must be the 741

The one in there now is the original. I did try a CD4049BE (unbuffered) but made no difference.

If it was the issue though - and if I short pin 1 & 2 - the volume should work and it doesnt make much of a difference...

I have a few other 8 pin dual Op amps in stock. Thinking maybe rewire one to the 741 single amp pinout and see what happens

Yes the sustain circuit is working fine. I tried both the 4049BE & 4049UBE. One didn't work at all. The other worked but didn't fix the issue.

Will check C8

That's mad that they used a 4049ub...

I have order some different brand 741's. Will report back next week...

Guys... so the new 741's arrived today. However the Ebay guy was advertising LM741 but sent UA741. Was pis*ed off

They do look like the better UA741's like Quench's though. So put one in and nothing - still the same low volume!

So decided before doing anything I'm going to replace the speaker. It measures 7.6 Ohm and you can hear the sounds so I wasn't convinced but thought - what the hell...

Changed the speaker and "Viola".. volume back and all is good!

Very weird cause the speaker measures ok etc - but there you go!

So U3,4,& 5 was faulty to get the card working and a new speaker to sort out the volume...

This project machine was seemingly standing faulty for over 10 years so I suppose some faults are just from lack of use and age...

It was missing the MPU, Driver Board, Rectifier and Transformer. I had all the boards in stock from repair jobs and sourced a transformer from Europe.

Yesterday I colour coded LEDs throughout, cleaned, polished and new rubbers - she looking great!

Going to start a cabinet repaint now. I want to keep this one in my collection as I am a Kiss fan

No - it actually looks fine... Have no idea why it's not working...lol