Robotron Sound Issue

jgeiger

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I just picked up a good condition Robotron yesterday and everything is good with the exception of the sound. All of the system tests report that everything is ok but all I get out of the speakers is a loud humming sound. I adjusted the volume but do not get much of a difference. Before I start digging in to it I wanted to see if anyone had any suggestions on what might be the issue or where to start diagnosing the problem.

Thanks for any help.
 
There is a diagnostic switch on the sound card. If you press it, it should start making one of the sounds over and over again. If you press it and it doesn't sound, then you will need to do some diggin on the sound card. If it does sound, you will need to power the cab down to get it to shut up.

Check the fuses on the sound card and check the voltages. The schematics give the test points and voltages you should be getting.

If everything checks out, it may be the PIA on the ROM card or the PIA on the sound card. If you have a logic probe put the cabinet into the sound test on the diagnostic screen and use the logic probe to check the cable from the ROM card. You should be able to see the lines pulse when a new sound is selected.

ken
 
Thanks for the info, that will really help me get started. The wires and connector on the volume control were kind rough looking so I wiggled them a bit and wiggled the volume control and now I can hear the game sounds along with the hum. With the volume control turned up all the way the game sounds are not very loud especially in relation to the hum.

Thanks again.
 
I just fixed mine by swapping the 40 pin socketed chip from my Joust. This is after I had done just about everything else!
 
The non-socketed one is a 6821 PIA, but when they fail most people socket that 40 pin animal.:rolleyes:

gotcha...Can you tell me what the replacement is for the cpu these days or do I have to find an oem chip?
 
CPU is a 6808 or a 6802. Normally the 6808 is used, but if the 6810 RAM chip is bad, there are a couple of jumpers you can switch and use a 6802 that has on-board RAM.

Last time I looked, you could still get them from Jameco.

ken
 
Thank you and didn't mean to hj this thread...just thinking this might be useful info! It solved my sound problem.
 
I installed a cap kit from Bob Roberts for the sound issued and it works great now. Thanks for all the suggestions. Now to figure out what is up with my Moon Patrol sound.
 
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