Repaired an SLT card (5603819) that had known faults

TWO OF EIGHT CHANNELS ON THE 3819 CARD WERE NOT WORKING PROPERLY

This is a card that was a spare but during testing I found that two of the eight identical channels were not working correctly. The circuits amplify a signal to drive up to 300ma of current at voltages of over 48V. It is used for solenoids in devices such as the console printer/typewriter as well as for large indicator lamps on the 1130 console.

FOUND BAD COMPONENTS BY TESTING ON THE BENCH

I set up my SLT testing workbench and plugged in the card. I verified what I had recorded from the earlier investigation - the circuit with B12 input to D10 output as well as the circuit with B02 input and D06 output were failing with the output always low. 

I worked my way through the card, using the schematic and comparing from time to time with the properly working channels. My first look at the schematic did not show a single component that would account for both failures. I checked each part in the circuit and watched its behavior as the input was toggled between 0 and 3V. 

It became apparent that the first transistor of the pair in a circuit was failing for both of the problem circuits. The first transistors are implemented on an SLT module 361497 which just consists of four transistors. The card has two of these modules and indeed one of the transistors in each module was bad. For the circuit driving output D06, the transistor that was bad was connected to pins 12, 1 and 2 while for the other (D10) circuit, it was a transistor on the other module at pins 10, 9, and 11. 

I verified the nonworking status using the diode checker function of my multimeter, then carefully removed the SLT modules from the card. With the module out it was even more obvious that the transistors had failed. 

PULLED TWO 361497 MODULES FROM A DONOR SLT CARD

I have a supply of old SLT cards I picked up on eBay and which I use as a source of components for failed parts. I pulled the two modules off after I checked that they seemed functional using the diode tester of the multimeter. Confirming that the module, off card, also appeared good, I was ready to install them on the 3819 board. I could have set up the curve tracer and double checked the transistor but I chose to move forward and just test the 3819 once these were in place.

SOLDERED ON THE TWO REPLACEMENT MODULES AND TESTED THE CARD

I subjected the card to a full test of all eight channels, since they all go through the modules that were replaced. They were all functional. The card is now ready to be used in a system. 

Two replaced modules along the bottom

KEEPING REMOVED MODULES WITH NOTES ON THEIR DEFECTS

I kept the two modules, each with one of the four transistors not working, as there may be a future situation where the bad transistor is not used on the SLT card. I also have a good module I had removed during an earlier repair session that turned out to not be the cause of the malfunction, so it is available for any repair.