Make Trax Sound Issue

flynn54321

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Just picked up a Make Trax... that has a sound issue
Game plays just fine - but the sound is screwed up.

I will try to explain... I credit it up - hit player one - and the music sounds like a radio station that is BARELY dialed in... you can tell that its intro music - but the sound is wrong and staticy... Any ideas of what to check? How to fix?
 
ok I am a restoration guy not a tech guy... so please dont get frustrated with my questions...
Ok so verify that the cabinet has the correct sound BOARD in it?
And who would I send it to to cap it?

Bradley

Cool game btw
 
Time to bump an old thread that from what I have read, never got solved. I have the same problem right now. It seems only one note - the high one - is present in sound along with some light jibberish. Either way it sounds like crap.

Make Trax is a single board game, unlike other Williams titles. C4, C5, and C6 are pretty much the only electrolytics in the sound circuit. I'd look there first. They are common 470u or 47u caps. Even rat shack carries those.

There are two sound roms - 1M, 3M. Try re-seating them.

Another fail point could be the sound pot (VR1, 1kohm). Did you crank that bad boy around a bit?

If you did make any headway, please share it. If I make any headway, I will do the same.
 
Just picked up a Make Trax... that has a sound issue
Game plays just fine - but the sound is screwed up.

I will try to explain... I credit it up - hit player one - and the music sounds like a radio station that is BARELY dialed in... you can tell that its intro music - but the sound is wrong and staticy... Any ideas of what to check? How to fix?

download this manual first if you havent already got it
http://pdf.textfiles.com/manuals/ARCADE/K-R/ and pick the make trax drawing set pdf file

turn off the game. remember to turn it off at the wall socket. mains voltages are present in the game and are dangerous for the unwary.

staticy sound could be a few things - start at the speaker. Page 12 shows the cabinet wiring diagram and as you can see there should be a series of connectors between teh board and the speaker. check em all,
and check the wire connections are solid. trace the wiring from the speaker back to the board and check where the wires go into the edge connector are also solid. pull the edge connector and clean the fingers on the edge of the board in the same spot as the wires from the speaker. if you see any loose or broken wiring, fix that first.

turn on the game.

page 4 of the manual shows the board layout. in the lower right hand corner, you shoould see a roound symbol marked VR1. thats the volume control on the board, so have a look at the board and tweak the volume control to see if changing the position gets rid of the static. if that s so, you may have a faulty volume control pot.

turn off the game.

also on page 4, at the upper left hand corder, you should see a rectangular symbols labelled 1M, and 2 to the right, one labelled 3M. these are the roms that DOkert referred to when suggest5ing you check if the correct roms were on the board. it is also possible that these chips may be loose in their sockets. if you slide a piece of wood the right thickness underneath the board under those chips, then try pushing them firmly into their sockets, and remove the piece of wood. careful you do not bend the board at all during that op.

turn on the game.

try the game again.

report back any change!
 
I checked all the 74xxx series IC's in the sound circuit with my DMM. I get pin 2 shorted on each of the 7489 RAMS, but I don't know if this means anything. Pin 2 is the memory pin of the RAM. Pin 2 is also not in the pinout of the actual sound circuit schematics. Is this irrelevant? If so, then nothing is shorted on in the 74xxx chips.

I thought I had the electrolytics on hand, but I don't. I'll need to check rat shack tomorrow. Boy an ESR meter would be nice...
 
Well I was going to see what I could find out - until a friend coughed up a working board for me... so i still have the bad one and havent done anything to it
 
I checked all the 74xxx series IC's in the sound circuit with my DMM. I get pin 2 shorted on each of the 7489 RAMS, but I don't know if this means anything. Pin 2 is the memory pin of the RAM. Pin 2 is also not in the pinout of the actual sound circuit schematics. Is this irrelevant? If so, then nothing is shorted on in the 74xxx chips....

yes the pin 2 connections for ic 2K and 2L (sound rams) have been ommitted for some reason. pin 2 is the Memory Enable control signal, when its low you can read from the 7489 , when its high you can write to the 7489, therefore according to the datasheet, if pin 2 is shorted all the time, then the 7489/74ls89 will only be able to read from, not written to.

check to see if the pin 2 change to HIGH (ir >2.75v) at any time - use a logic probe for that. you will need to trace pin2 connections on 2K and 2L to see what it connects to. the ic that controls the read/write cycle may be crook, or, you may have a short.

EDIT: I pulled out my 3 make trax boards - oops. pin two is grounded. back to square one on 2l 2k..
 
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Them being grounded means those chips are okay.

I replaced the electrolytics - no change. It seems all I get is the two highest notes and some occasional chattering sound. I also noticed that AMP1 (the sound amp) has been reworked and/or replaced at some point. That leads me to think it might also be the culprit. The fact that I am getting audio though...maybe the amp is fine.
Here's the data sheet:
http://hiyes-tech.com/Datasheet/MB3712.pdf

The sound circuit only shows a single input - pin 6. I need to pull the board again to trace pin 8.

The socketed 2 chips are really the only other things. I can probe them, but I'd just be shooting in the dark.
 
Quick question: I think I have a better grasp of testing on these boards. I have an idea for an easy way to test the socketed roms and the amp at the same time. If I probe the input of the amp (pin 6 '+') with a pair of headphones I have rigged up as an audio probe, I should hear the pre amplified game audio, correct?

Then I can probe the output of the amp the same way to check everything up stream of the amp, and the amp itself.

If I hear all audio at the input side, the sound circuit is fine. If it is messed up, then the socketed waveform chips are messed up. If the audio on the output side of the amp is the same as what I hear at the speakers, then I have a bad amp. If that audio is fine, I have something bad up-stream between the amp and the speaker.

Can one of you repair pro's check my logic on this?
 
I use an oscilloscope to check the raw waveforms. You can compare the inputs to outputs on op-amps and the final amplifier to try to find out where the distortion is coming from.

For an audio probe you need a high impedance input on it so raw headphones won't work as they'll load down the circuit excessively. If you had an amplifier circuit there with the headphones then you could use that and it would work well.
 
[Curiosity kills another cat] I pulled the MakeTrax schematic and took a look at it. It appears that there is only a single amplifier (3712) attached via the volume control to a 4 bit D/A chip. The copy of the schematic that I have has a couple of flaws. The first is there is a glitch in the scanning. The left side of the D/A chip dropped the 1 in front of the 2 & 3 control inputs, they should be 12 & 13. Second it looks like pin 4 of the amp, which should be going to ground, appears to have a +5V digital symbol on it. If that is the case then it is only being powered by +7V as pin 2 (Vcc) is attached to +12V. A very curious circuit. In any case, it looks like it will take a scope to find the problem unless you start at the amp and replace everytimg backwards until it sounds good. Which won't be very far back.

ken
 
Well I've checked everything but the two socketed chips and the amp. The amp has been replaced, because there is solder rework there. Unfortunately, I can't find a source for 1M and 3M. If I had a source, I'd just go ahead and replace them.

All I have is an Ozifox pocket scope. It generates a very basic scope curve. Would that be good enough to test with? I've really only ever used it as a logic probe. I don't really know how to use it good enough to do anything else.

Any advice on that tool would be most helpful.
 
Just because the amp has been replaced does not exempt it from the suspect list. AT this point, try the scope on the input pin of the amplifier. It may have enough resolution for analog signals.

ken
 
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