Total Recall Logic Card CF82E88 keeps burning out SSL 4000 E/G

[Cavern Sound Sudios]

SSL 4000 E/G

My Total Recall Logic Card CF82E88 keeps burning out the 10R resister (R6) 

When the S9E ( the 10 way ribbon that goes from the 88 card and daisy chains from bucket to bucket ) and the B3  ( 6 way square on the 88 card ) are both connected the voltage across the resistor (when all buckets and the master section are powered up) is 1.18v and everything works fine

When all the buckets are off and only the master section is powered up the voltage across the R6 reverses polarity and measures at -3.3v and the resistor burns out.

This scenario is repeated even when all the channels are out of the console and all the cards are removed from the master section

[Dave Dicson]

If you have the wider keyboard, the Recall driver circuitry is ached to the bottom of the keyboard PCB which maybe where your problem is. If it is the shorter keyboard, the Recall driver circuit is on a small circuit board under the center section. Maybe an opto isolator?

[radardoug2]

There should be negligible voltage across that resistor, calcs indicate you have more than 100mA flowing in the 1 volt condition, and 300 mA in the 3 volt condition. Does this happen on every card in every module? Sounds to me like you have a short there or a partial short. Pull the card and set it up on bench supplies.

[Cavern Sound Sudios]

Thanks guys

Only happens on the 82E88 card,

I have it on the bench now, I will put 18V DC into it and see what i get across that resistor

Standby

[Cavern Sound Sudios]

18.5 volts into the 88 card on the bench and i get 1.3 volts across the resistor

when its In the console i get 5.4V across it

[Cavern Sound Sudios]

Every time i drop a channel in to a bucket ( with the bucket switched off) the voltage across that resister rises by 0.08v

So that times 56 channels = 4.48v across that resistor which burns it out, incidentally when i turn all the buckets on with all the channels in the voltage drops to 0.7 and everything is fine, everything on the console has been removed and disconnected except the 88 card and 1 channel

Any ideas where the short might be ?   

[radardoug2]

I dont have that schematic here, but it sounds like you are somehow backfeeding all the modules. I take it this is a single card, not the one fitted in each module? Look for a bussing path from the card to all modules. Also, it seems like the card is drawing a lot, more than 100 mA by itself. This could indicate a fault on the card.

[Cavern Sound Sudios]

All 56 multiplex cards on all 56 channels gives me the same result across the resistor on the 88 total recall card

[radardoug2]

OK, so this is one master card on the total recall. Read my email again and understand what I am saying.

[Cavern Sound Sudios]

Yes 1 x total recall master card

I have replaced all of the CN17 and 4016 chips on the 88 card, I will replace all
the transistors today

[horizonsound]

I think you are approaching it the wrong way looking at the voltage across the resistor alone.

There is a high chance there is a short somewhere between the +18V and +11V rails. The TR along S9E works on these two logic levels.
This issue could be in my experience one of a few causes.

A blown BC212 transistor giving a dead short across it. Have they been replaced, and if so, ensure that if they have been replaced with BC212B, in lieu of the original and unavailable BC212L transistors, that they are rotated 120° CCW to match the correct pinout to board layout. Common mistake.

One of the 10way S9E ribbon cables has a short in it. check all links between boards. remove sequentially and see if this resolves it. As I understand, your issue is only on the left hand side of the console (1-24).

There is a short due to some foreign matter in the back plane edge connector. check closely.

Some photos might assist.

Anthony.

[Cavern Sound Sudios]

Thanks mate

A blown BC212 transistor giving a dead short across it. Have they been replaced, and if so, ensure that if they have been replaced with BC212B, in lieu of the original and unavailable BC212L transistors, that they are rotated 120° CCW to match the correct pinout to board layout. Common mistake.

This i haven't checked, I will look at that today

One of the 10way S9E ribbon cables has a short in it. check all links between boards. remove sequentially and see if this resolves it. As I understand, your issue is only on the left hand side of the console (1-24).

Issue is on both sides master ( CH 1 -56) , i have replaced and moved around all of the S9E cables, including the Y split coming from the 88 card

[horizonsound]

This is what you need for the BC212B transistors.





Anthony

[Cavern Sound Sudios]

We really need a mod so the multiplex cards on each channel receive their 11v when the master section is powered up regardless of the buckets being switched on or off

There is no short on the console
The 88 card is functioning as designed

I will have to replace the 10ohm resistor on the 88 card with this
https://www.jaycar.com.au/rxe075-ptc-fuses-speaker-protection/p/RN3460

I have a  0.08v rise in the voltage across R6 for every channel that is inserted when the buckets are switched off

[radardoug2]

Surely the multiplex cards should get their 11v from the module they are on?
If not, mod them so they do.