Been working on my new acquisition, a bally Spectrum. Once it has fired up and all ready to go there is a terrible loud hum coming from either the main transformer, or something nearby in the bottom of the cab.
When you first switch on there is no hum noise at all, it's when the machine sparks into life, says a few words and is basically in attract mode, then the hum is there and it's loud.
At first I suspected the sound board and speaker, but I disconnected the speaker from the sound board and the hum is still there.
I disconnected the power from the playfield (by unplugging the plug on the power board in the bottom of the cab labelled "playfield" and tried that - machine all fires up ok - backbox and all boards in the backbox going, sound working, etc, and NO hum?
So, seems to be the power draw onto the playfield. No coils are locked on, just a load of incandescent lights flashing away nicely. I have a couple of thyristors out on the lamp driver boards, but this results in a lamp being out, so doubt that is the culprit, but......
Checked all other stuff, fuses all ok, non blowing or blown.
Anyone come across this before, or got any ideas please?
Many thanks,
Alan
When you first switch on there is no hum noise at all, it's when the machine sparks into life, says a few words and is basically in attract mode, then the hum is there and it's loud.
At first I suspected the sound board and speaker, but I disconnected the speaker from the sound board and the hum is still there.
I disconnected the power from the playfield (by unplugging the plug on the power board in the bottom of the cab labelled "playfield" and tried that - machine all fires up ok - backbox and all boards in the backbox going, sound working, etc, and NO hum?
So, seems to be the power draw onto the playfield. No coils are locked on, just a load of incandescent lights flashing away nicely. I have a couple of thyristors out on the lamp driver boards, but this results in a lamp being out, so doubt that is the culprit, but......
Checked all other stuff, fuses all ok, non blowing or blown.
Anyone come across this before, or got any ideas please?
Many thanks,
Alan
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