High Speed Background Music

[PinWiz]

I own a High Speed that the background music is out on. It gets the proper voltage, and everything else works except for background music. Any clue?

[Strangeways]

Is it as simple as enabling the background music in the setup ?

[PinWiz]

Nope. That isn't an option for it. In the menu for the different tests, Music Test used to play the entire music track (when it worked of course) but now nothing.

[Strangeways]

OK - so the music test also fails - but in game sounds are still present.

[PinWiz]

Correct. I have tested to the best of my ability to make sure the chips input and output what they are supposed to. I cannot remember what the output tests ended up as(pretty sure they checked out fine) but input was all normal.

[Pinball Fixers]

High Speed uses a "Background Sound Board" for the background sound. The in game sounds are generated on the CPU's sound section.

So, the first thing I'd be doing is re-seating all the cables to the background sound board, and the other side of them on the CPU.

Next, Make sure J1 on the Background Sound board has the following on the pins:

Pin 1: +5 Volts
Pin 2: Ground
Pin 3: -12 Volts
Pin 4: No connection

If all this checks out fine and you've re-seated the plugs, then it may be the MC1458 Op-Amp (U9), or the MC1408 DAC (U1). At this point you will need to test it in another machine, or on a test bench.

It may also be the IC sockets. Williams were still using the cheap sockets at this stage, so it would be best to replace them. It's the first thing I do after the initial testing on my test bench.

[PinWiz]

Well, I have tested voltages, it is fine. Reseated connectors a lot because I had been switching it in and out with another one for awhile that the background music was working on and also died. The only socket is the one I added for the oscillator crystal that I replaced. I could check the background sound ROM socket though. If I had a clue on using the oscilloscope I recently got for free I could do some logic probing. If I can get the U1 chip I could try replacing it too.

[Pinball Fixers]

I've got some of the DAC0808 chips which are a direct replacement for the MC1408 (in fact the chips have both part numbers on them).

PM me if you would like one.

[PinWiz]

Well, I haven't gotten around to it yet but I think the socket issue is it. Lately, I have been spending my free time working on some arcade games to sell ASAP. Most have little issues and I am getting around to them and more importantly CLEANING them so I will do a check on the socket. I am pretty sure IF I go to replace U1 I'll just order it. I have some other things I need to order anyways.

[Strangeways]

Well, I haven't gotten around to it yet but I think the socket issue is it. Lately, I have been spending my free time working on some arcade games to sell ASAP. Most have little issues and I am getting around to them and more importantly CLEANING them so I will do a check on the socket. I am pretty sure IF I go to replace U1 I'll just order it. I have some other things I need to order anyways.

Let us know how you went when you have fixed it 

[PinWiz]

I don't know if it will fix it it though. I'll make sure to keep you all up to date. I hope to get it working soon as I have seen myself do worse without it (wow I know that sounds weird but it really pulls you into the game like Asteroids and Space Invaders music).

[Nug]

a socketed crystal is asking for trouble in my opinion, id hard solder that one.

regards

[Pinball Fixers]

a socketed crystal is asking for trouble in my opinion, id hard solder that one.

Good pick up Nuggy... Didn't even notice that... lol

Yep, definitely solder the Crystal in.

[PinWiz]

Heh heh, Could I ask why to solder in crystals? I am pretty sure U5 is fried. If running for 5 minutes it becomes HOT. I can still touch it but with no draw on it that isn't normal. The voltages coming into the board are at 4.88 volts and -14.58 volts unregulated. The -14.58 volts goes right to the volume control so under any circumstance that isn't the problem. The 4.88 volts is all fine to the chip so who knows. I will be replacing sockets and U5 soon.

[Nug]

the crystal, being a frequency type part is susceptible to noise which screws up signal oscillation leading to a halted processor, but a hot chip is always suss, now to really diagnose pull the solder off of +vcc and gnd of hot chip and measure with transistor setting, if is under .4 is most probably screwed!

-dont let the legs touch the desoldered tracks/pads

regards
nug