Quad Eight 137 HELP NEEDED

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bluezplaya

Well-known member
Joined
May 7, 2006
Messages
676
Location
Alabama Gulf Coast
I could sure use some help right about now! I have racked a pair of Quad Eight 137 cards. They both have the original 3442 transformers for outputs and I'm using the Cinemag 3440a input transformers mounted to JLM Go-Between Plus cards with no zobel resistor. I can't seem to find a specific schematic for the 137 card but have been looking around the forum and finding schematics for the 127 card, and some pinout info.

After getting the voltages correct on the JLM psu at +/-28V and 48V, I put the edge pin connectors on the cards and within seconds R11 (36r) on channel 1 was fried in a puff of smoke. I unplugged channel 1 and I turned the power back on to test just channel 2 but all I got was some hum and no audio signal.

So here is the pinout I've got:

1 = +28v
2 = -28v
3 = ground
4 = out trans (-)
5 & 6 shorted together
7 = out trans (+)
8 = n/c
9 = leg 2 of gain pot
10 = leg 3 of gain pot (330r in series with pot)
11 = n/c
12 = n/c
13 = input (-) from JLM GB
14 = input (+) from JLM GB

I'm using mic cable to connect the XLR ins to the Go Between input but using two wires twisted from the mic out (+ and - from GB) to the 137 on 14 and 13.

I'm using mic cable to connect pins 7 and 4 from the 137 to the XLR out. The shield is connected to the XLR but not connected to the 137 anywhere.

Any insight or help would be tremendously appreciated.

Adam
 

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See attached.  It might  be the schematic for the 137.  If you don't mind verifying, it would be nice to know for sure. 

R11 looks like 3R6 on the schematic. 

Did you test the cards by themselves before hooking up the JLM cards?  If not, I would do that now.  Also, might want to check the transistors, especially the output ones on Ch1. You can use the diode function of a DMM, even in circuit.  Any oddball ones you can pull out and check them isolated from everything else.

I think the cards will work on lower voltage also, might be better to start with so to create less heat.

 

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That's the same schematic that I have and am going by. I did not check the cards themselves without the JLM cards. I will check the diodes out with my multimeter.
 
Any luck? 

BTW, when I mentioned using the diode function, I meant checking the transistors as two diodes connected at the base.  Here's a tutorial with pictures and all.  I've done this with 2520's, these cards should be easier since they've got more space.

http://www.amb.org/forum/howto-bjt-sanity-check-t59.html
 

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