Radial Workhose WM8 Mixer Card Trouble Shooting

[Jamin Lambiris]

Hello Everyone is been a while.

I have successfully modded  11 mixer Cards over 3 Workhorses. Not including the master sections.

Here are the Problems

The Relays are not turning on.

So Far I card changed all the Electrolytic Capacitors to Nichicon UHE's
Removed all the Zener Diodes tested them and put the back.
Removed all the NPN Transistors tested those and put them back.
Replaced burnt Resistors with new ones.
Replace Switching Diodes with new ones
Removed Relays from another card and put them in the one, The other card works flawlessly.

I have tested the voltage at all 9 Test Points same result in all 9 locations 15.75V.

However R1 and and D1 which are in series I measure a less 14.80V These two are connected to the positive rail.
R3 and D5 are the same but connected to the negative rail and measure 14.75V

The other 11 working modules measure over 15V in both positions.

Does this have anything to with why the relay wont open and what could be causing this voltage drop.

Thanks

 

[Jamin Lambiris]

One other thing. FB1 looks different to FB2 the longer lead has a white filling that FB2 doesn't have.
Is that a sign of failure or am I clutching at straws to find out what is wrong with this card.

Thanks again.

 

[metalb00b00]

those look like Panasonic TQ2 relays, though the laser marking is unclear, so can't tell if they're 5V or 12V (measure D3 cathode pin to find out which one)

FB1 & FB2 are ferrite/iron beads, to keep out radio frequency interference.
If you pull them out and replace with jumper wires, that's all you lost, the audio circuit are not affected.

if the relay don't switch, you should check around that area, for cold solder joints, or shorted joints.
if all is well, yet they still don't switch, replace them.

a 0.1V to 0.5V deviation in 15V supply is fine.

 

[Jamin Lambiris]

Yes they are. TQ2-24V ATQ204.

 

[metalb00b00]

have you checked the 24V supply point/copper trace for continuity of the slot you insert this card to?
have you tried swapping slot or swapping this card with a working one?

 

[Jamin Lambiris]

Yes I have. The other cards work in that slot and I have also put this card in the other slots too.

 

[Bo Deadly]

Make an extension cable so that you can test things with a multimeter or scope with the card outside the unit. That should make it pretty straight forward to diagnose. Just check for voltage changes across the relay coils and then trace back to the supply and ultimately the switches (presumably the switches control the relays).

But if both relays are affected that sounds like a supply issue. Does the supply withstand a load? Best guess at this point would be a bad solder joint related to supply or shared switching logic if any. Do the relays click momentarily if you flex the board a little with a finger?

 

[Jamin Lambiris]

I used to pencils to put pressure on various parts of the board no relay clicks.

 

[Jamin Lambiris]

Update I just reflowed every single solder joint on the card but still no change.

Does anybody have anymore suggestions.

Thanks

 

[metalb00b00]

Update I just reflowed every single solder joint on the card but still no change.

Does anybody have anymore suggestions.

Thanks

did you do the test with all cards inserted?
if so, try removing one of the working card, and see if the relays this time will click. this is to check if the 24V supply has enough juice.
if they still don't engage, pull them out and replace them.
if replacement also don't engage, and the supply trace is not broken, then the part responsible for activating the relay is not working.

 

[Jamin Lambiris]

Each card has it's own set of relays. Including the Master Card.

I have only been using the one card at at time. To clarify the Power Suppy is 16V the relays have 24volt Markings.

 

[Jamin Lambiris]

I got in working again. Turns out there was a fracture on the board.