Fathom sound problem

[solar value]

Hi all,

I have lost the sound on my Bally Fathom.

The LED on the Squawk and Talk board is locked on.
The MPU is OK (7 flashes).
No sound but with the volume up there is a hum.
When I activate switches during a game I get an faint 'blip' sound.

I have re-seated the connectors on the S&T and J1 and J2 on the MPU.

From what I have read it seems like there could be a faulty component on the S&T board. Anyone have any ideas?

[Boots]

Hi all,

I have lost the sound on my Bally Fathom.

The LED on the Squawk and Talk board is locked on.
The MPU is OK (7 flashes).
No sound but with the volume up there is a hum.
When I activate switches during a game I get an faint 'blip' sound.

I have re-seated the connectors on the S&T and J1 and J2 on the MPU.

From what I have read it seems like there could be a faulty component on the S&T board. Anyone have any ideas?

Sounds like a reset problem, this is from the pinrepair guides:

S&T Board Reset/Boot Problems.
The Squawk and Talk board is not unlike the MPU board. It too is a computer, with a reset section, and an LED which "flashes". The flashes determine if the board has a "boot" (turn on) problem. But before the board boots, it needs to "reset" (hold the CPU's /Reset line low until +5 volts can stablize, and then allow the /Reset line to go high and start the boot process).

Often this reset process never happens, and the S&T board never boots (LED locked on). Since there is no battery on this board, battery corrosion usually isn't causing any problems (unlike the MPU board!) But the reset section can have faulty parts. One common thing that fails is capacitor C1 (47mfd 16 volt). Replacing this part, or the reset transistors, can often solve a S&T boot/reset problem.

[solar value]

Thanks Boots,

I guess I'll start by replacing C1. Where are the reset transistors?

[Boots]

Thanks Boots,

I guess I'll start by replacing C1. Where are the reset transistors?

I think the layout is on page 33

mirror2.ipdb.org/files/477/Bally_1983_Centaur_II_Manual.pdf

[solar value]

Great, thanks, I found that page in my manual.

I also had a look at the Bally Repair Manual (which can be found here):

http://www.scribd.com/doc/47481567/pin-repair

On page 82 it says the probable causes of a locked on LED are:
faulty U5
faulty U15
leaky C1
open R1
leaky CR1
faulty U17

Can I test any of those components with my DMM?

[Strangeways]

Reseat the socketed ICs. Common problem. There is a rebuild kiy available from GPE - but that is more for a variety of issues than reset.

[solar value]

OK, finally have something to report on this.

I replaced all the components listed above which the Bally repair manual said were likely causes of the LED locking on. Unfortunately this did not fix the problem. When I visited Benpin the other day he mentioned that I should try replacing the 6821 chip at U11. So the very last thing I tried before I was going to send the board away was to switch U7 and U11 (as I didn't have any 6821s lying around). Well, now instead of a locked on LED, I have one flash. So I'm guessing one or both or these 6821s must be faulty.

So it was very frustrating that I changed out all those other components for no reason but good to have made some progress.

[solar value]

Just to finish off this thread I have a final update. Benpin dropped over some 6281 chips today and I replaced U7 (which was originally in the U11 position when the LED was locked on). The sound is working 100% now.

Thanks everyone for your help with this, special thanks to Benpin.