Firepower Sound Board

Interesting repair, not one you see too often.  This is a sound board for Firepower that came in for repair. The owner had a Firepower machine with no sound boards, bought these used out of a Black Knight. The initial complaint was that it was getting no sounds using a Firepower rom set, but worked fine with a Black Knight rom set.  Sorry for the shadowy picture,  bad lighting in my workbench when I do these late at night.  The better photos are during the day.  But lets get to the repair work, eh?

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Started off with Leon's test rom.  Yes, he has one for these sound boards too,  ties an LED into an address line for the characteristic blinking.  This board would blink for a few seconds, then lock up.  Other times it would just keep blinking,  but if I pressed on the chips in their sockets, it would lock up. 

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The problem, Scanbe sockets of course.  Thankfully this is a very simple board in comparison to the others in a machine, only two sockets on the sound board for the CPU chip and the rom chip. I kinda knew this was going to be an issue when I installed the test eprom,  as there was very little tension in the socket.  You can really feel it when a socket goes bad sometimes.

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Easy fix so far, install a pair of good stamped sockets, and the test rom works perfectly.  It also has a test of the 6810 ram chip, which also checked out ok. 

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While I was at it, I also replaced the power connector.  Again, typical Williams.  Pins trimmed too short, no mechanical strength, and the solder joints crack up and loose conductivity.  This wasn't causing problems yet, but would be eventually.

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So, I throw it into my Black Knight for a live sound test.  Sound portion works just fine,  great!  Attach the speech board, rejumper it accordingly, and zero speech response.  Sound working fine, but no speech.  This narrows it down a lot actually.  It means the mixer op-amp at IC2 is working fine.  Very little hardware on the speech board,  so first thing to check is the eproms.  On a hunch I pulled the labels.  AM2732 eproms.   Whoops!   Williams speech boards use 2532 style eproms.  Same capacity, but incompatible pinout. 

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Though they are scanbe sockets, they still had good tension, so I burned a set of the correct 2532 chips, and installed them.  Speech kicks in just fine,  not a hitch to it. 

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Just a bit of interesting thoughts about this repair.  On the one hand it's the usual Williams issues of sockets and connectors, followed with incorrect parts in a previous bit of rework, when the roms were swapped.  Par for the course really,  it's almost invariably a socket, connector or previous work that causes the problem.

But then again, you almost never see these sound boards go bad.  Driver boards have their 6821 PIA chips get fried all the time, but you never see them go bad in sound boards.  Why is that? I have my theory, and you've heard me say it before.  Heat and battery corrosion.  Driver board PIA chips are right below the CPU board batteries, and right above the lamp matrix transistors/resistors.  I've seen driver board after driver board come through here, and they all have some kind of heat damage coming off those lamp resistors.  CPU board is immediately above the driver board, connected to it in fact. Heat rises, stressing the interboard connector. 

Sound board is all the way on the other side of the backbox, and not thermally coupled to any real heat source.  Sure, the 7805 voltage regulator gets hot at times, but nowhere near as badly and it's got a lot of heatsink attached to it.  It's also right next to the backbox vents, so it's going to have more cool air available too.

Why am I rambling about this?  Simple.  If you want a long-term reliable machine, you need to cut down on all that backbox heat.  It's killing your boards, killing your displays, and killing your backglasses.   The two biggest sources are the lamps and the driver board transistors.  On my Black Knight pages I have a couple of ways I've dealt with this.  Biggest one is swapping to LED's,  the other is a MOSFET swap on the driver board.  Doing these cut the power usage down to less than that of your average home light bulb.