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

[Chris Simon]

For those of us following along at home, it might be good to know the function of R6; i.e. on what rail. I don't know about the '88 card, but on the G series '323 card, there are 1K pull-down resistors that will hold each TR line in S9 to 11 volt logic low, regardless of the ribbon being connected to the buckets. I trust all the voltages are present on the BICC and directly on the CMOS chips?

[Cavern Sound Sudios]

They do, but when the bucket is switched off and the 11v isn’t being supplied the multiplex cards pull too much from the 88 card, do you know if the 11v is supplied to
all of your buckets when only the master section is switched on ?

[radardoug2]

When you switch a bucket off, all supplies are removed.

[Cavern Sound Sudios]

Thanks i really appreciate the feedback, please shout out any suggestions

The 11v rail in each bucket is only present when the buckets are switched on ( thanks for that clarification)

The R6 is located on the Total Recall Card and it is a 10Ω fuse for the +18V supply to the 88 card, it provides positive power to the T1 & T2 chip

NOTES:
The 88 card receives its power directly from the PSU passing through the master toggle On/Off switch
(There is is a direct cable to the 88 card from the master section toggle ON/OFFF switch)
The card has +18 -18 11 & Ground via a black 6 way connector
I can completely remove my master section from the console and every bucket PCB and the 88 card still receives the +18 -18 and the 11v

When the S9E ribbon cable that feeds the 88 card to the buckets (daisy chaining from bucket to bucket) is unplugged or plugged into the 88 card everything is fine without any channels in the console.
When the S9E is plugged in and all channels are fitted into the buckets everything is fine as long as the bucket power is on and the Multiplex cards are powered up

When the S9E is plugged in as you add each channel to a bucket ( bucket power switched off) the voltage across the R9 increases by 0.08v ( 56 channels x 4.48v )

Two experienced technicians and myself have all checked the 88 card and it seems to be working fine, all the chips have been replaced and all the transmitters tested, everything passed successfully as working
 
If i remove the 88 card and a bucket PCB from the console and bench test i i get the same results
I have also tested it with another persons channel strip and also with someone else's multiplex card

I will replace all of the transistors on the 88 card with the ones Anthony suggested and then the card has just about been completely rebuilt.

My total recall card i have is CF82E88 and my multiplex cards are CF82E03 

I could mod the 88 card by replacing the R6 with https://www.jaycar.com.au/rxe075-ptc-fuses-speaker-protection/p/RN3460
I really need another  CF82E88 Total Recall card to test against

In shot - The multiplex cards are causing the 88 card to draw too much voltage across the R6 whenever the multiplex cards are not powered up


I need a coffee

[radardoug2]

The thing to do is establish what pin on the ribbon is pulling the current. You could do this by studying the schematics, or by making a little adapter by the master card which allows you to disconnect the wires one by one. Easy to make with a couple of sockets, some wire, and a particular type of prototype pcb. You can get a prototype pcb that is laid out as two interlocking grids which bus every second pin hole. This allows you to put two headers on and all the same pins get connected. Then, in the middle of this, you could put in a bunch of links. You can then disconnect one or all pins at will. And its only a 10 pin header. Start by disconnecting aal the obvious suspect pins, and then connect one at a time. Once you know which line is drawing the current, you can probably modify each multiplex card. Some work to be done!! Send the bill to SSL for not designing it properly!

[horizonsound]

Update on this issue..

The S9E cable sends the address line logic down to the module back planes, utilising logic low (+11V), and logic high (+18V).
The reference voltage for logic low is not sent down the S9E line but is instead picked up off the +11V from each module / bucket.
When the bucket is turned off, the logic low is floating, creating a 55mA draw on the 88 card.
When six buckets are turned off, that adds up to 330mA, equating to over 1W on the 10ohm fusing resistor.

I tested it on my console, and the 88 card's fusing resistor started heating up, pulling 330mA.

I'd never noticed this before as I keep all the buckets on all the time.

Anthony.

[radardoug2]

Can you post schematics of the two cards? Presumably the address lines go into logic, probably cmos? Maybe you could put diodes on the lines or some resistance?

[horizonsound]

The address line are pulled down to +11V at the CF82E88 card end via a 1K resistor , then go through a current limiting resistor (15K) at the CF82E03 multiplexer end, and in to some 4000 series logic, also running at the same logic levels (+12V / +18V).

I was thinking sending +11V down the spare pin 10 of the S9E, which goes direct to pin 10 of the S21E in to the multiplexer card, and then either a pull down resistor on each line or diode as you say.

Hassle is that you would have to do that on every card in the console....or just keep all the buckets on. Not a big deal when a 48 channel pulls less than 500W using a switchmode.

Anthony.

[radardoug2]

Two things. Theres a set of resistors shown on the input to the multiplexer card, change this value up? Or second, just put a switch on the driver card to switch the 18 volts off? Or put a current limiter (2 transistors) in series with the 10 ohm, set above the normal operating current. That one would be set and forget, and only 4 parts!

[horizonsound]

Looking deeper, it appears the G series Total Recall Bus Driver addressed this issue by using a 1.2ohm thermistor in place of the 10ohm fusing resistor.

https://au.element14.com/epcos/b59910c0130a070/ptc-thermistor-1-2ohm-80v-th/dp/3407757?ost=b59910c0130a070

Anthony.