Just added the wonderful PSU5 in my PZ backbox to replace that super hot LM323K.
Before doing that switch I noticed a lot of speaker pop and crack when powering on and off the machine.
After the switch the speaker pop and crack got much worse, so I decided to fix that somehow.
I seached Pinside and found some folks had made dual relay boards where one relay turned on slow and the other turned off fast. (speaker wire is run through the relay contacts)
Those boards use a bridge rectifier to power the relay coils and they tapped off the audio board AC power connector.
I was a little worried that if the bridge rectifier failed smoke would happen, so I looked around for other ways to accomplish the same thing. (also I really wanted to use parts I had lying around)
Well, I had just repaired my CPU and got to know the Blanking LED since it was not acting correctly until I replaced the bad IC that fouled the Blanking logic.
That LED (and the Blanking logic) seems like it was a perfect delay to hold off the power ON speaker pop and crack.
So, I added a relay to the Blanking (ENABLE) open collector transistor Q1.
(make sure R98 is 1K, my board had a 10K there from the factory)
OK, so that takes care of the power ON pop and crack, what about the power OFF pop and crack?
The only way to solve power OFF pop and crack is to get the speaker disconnected as quickly as possible after the power switch is turned off.
I had a few 120V AC relays in my junk box, so why not disconnect the speaker by the AC power?
So, my power box in the cabinet has a courtesy plug, so I decided to just power the relay from there.
I wired the plug to be live only when the pin is turned ON.
There is a QUENCHARC across the AC coil, I doubt that is really necessary. (it was already connected so I left it)
After installing all that stuff my speakers are truley silenced with power switching on and off.
I figure the same technique could be used for WPC pins. (some variation required for different speaker configurations)
For WPC Dot Matrix (like PZ) the speakers are all in series, so you just open the circuit anywhere.
Someone else could post the corrrect speaker switching method for other WPC types.
CAUTION ! These mods are not to be tried by persons with no electrical or electricic experience.
(I can't imagine too many that restore or work on pins could not do these mods safely)
BTW - These mods can be easily reversed too. (I used FastONs for wire connections)
Comments are welcomed, this just one way to solve this issue.
I'm sure others have solved this in other ways. (share your knowledge please)
idec RY4S-UL (AC relay)
NAIS JS1-6V (6V relay)