Hi All,

So picked up an Eight Ball Champ 1985 yesterday. Have fixed about 20 different faults from playfield, flippers through to the CPU faults etc. The last thing was the sound board (SB). Got it fixed last night to the point where all sounds and speech is working fine but there is a loud hum on the speaker. The SB has had it's capacitors replaced before apart from a couple of 2uf ones.

I put in another SB from my Eight Ball Deluxe LE and the hum is gone so definitely the SB.

I swapped over from the good board the 2uf old caps that hadn't been replaced but no difference.

I have hung the board off the chassis but no difference.

I swapped the 5v transistor (heat sink) as they were different on both boards so just wanted to make sure it wasn't that but no difference.

I re-replaced the large caps but no difference

The speech and sound small Pots are working fine

The door Pot is working fine (cleaned and lubricated anyway) but as the fault is on the SB no real worries here

Volume goes up and down as it should with all pots

Resoldered the header pins and checked the earth connection

But this ?$$!!!£$^&** Hum will not go away.....

Any ideas???

Hi Quench

The hum goes up and down when adjusting the "speech" pot - not the sound pot. TP3 i'm getting 14.9v

When turned down you can still hear it but much lower obviously but it is definitely changed up and down by adjusting the speech pot

TP3 - I'm getting that 14.8 to 14.9 on both AC and DC settings on the meter.

TP4 - -8vdc to -8.3vdc on both AC and DC settings on the meter.

All readings on those test point come up DC even when I change to AC

The ground is good - weird.

I'm getting -4.9vdc on my good board so going to swap it over and see as I only have the 7805 positive 5v in stock... Back soon (the caps are good)

That's it sorted! LM7905 buggered.

Cheers Mate - thanks for the help