Well typically Gottlieb (
) the audio output chip on System 80 games (LM379) was obsolete even while the games were in current production! Unbelievable. Seriously I think one of the main reasons Gottlieb 'lost the plot' when the era of electronic pinballs hit was they had some really bad advice regarding electronics. Anyway, back to the problem at hand.
Gottlieb released some service advice suggesting a different chip could be used but, yet again, the replacement one chosen couldn't have been further from 'the best choice'. Their mod required track cuts and several jumper wires - not pretty! I guess it did work though.
I started looking at a replacement board for these IC's a while back but I mucked up the PCB layout and transposed a couple of wires. When I discovered this (AFTER I had made a few test boards) I chucked the whole lot in the corner, disgusted with myself and moved on to other things.
Recently a member asked me about this project as it is mentioned on my website somewhere? Enough time had passed so I wasn't as annoyed with myself so I dragged the project out and corrected the errors. I double checked that the circuit would actually work and referred to the manufacturers spec sheet for some biasing advice.
I had originally found a 'quick fix' elsewhere on the web using a similar chip but it still required adding wires and resistors to the main PCB to perform the mod. I dislike that sort of thing and you will find that all of my 'add-ons' and repair boards don't require any modifications to the original game and in most cases no soldering either so the boards can be returned to the original condition quickly and easily should the correct part/s be found one day. This module has the required biasing resistors built right onto the module itself - no external parts needed.
In this case the original dud chip has to be removed and this module is a direct replacement requiring no other work and no other wiring or parts at all.
Here are the batch or 'new' boards I made (with fingers crossed this time).
I built two of them up initially:
Then I made a jig that replicated the Sys 80 motherboard exactly (well, the audio output section anyway).
I was greeted with a loud "BRAATTZZZZZZZ" when I touched the input pin so that was a good start. Connected an audio source from a generator and the CRO on the output and the amplification was quite clean with so little distortion that it certainly won't bother a pinball amplifier.
So I have another small add-on available - must be time to update the website I guess................
Price wise - I guess about $25 each for a complete assembled module, tested, ready to solder straight in.
