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8116A Code 42

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Mick B:
Hello, I'm still reading. I removed U-37 and took voltage readings @ U-32, U-33, U-37 SOCKET sans the chip. I will do this again after I put in the new MC100103. U-37 chip. The settings are the same.

PINS U-32

4(I)     -2.260
7(I)     -0.461
10(I)   -0.463
12(I)   -5.3
13(I)   -0.810
 
2(O)   -0.813   
3(O)   -1.773
5(O)   -053.6mv
6(O)   -050.6mv
9(O)   -0.816
11(O)  -0.816
14(O)  -1.773
15(O)  -0
VCC PINS 1 & 16 = -013.6mv
VEE PIN 8 = 5.3

PINS U-33

4(I)   -4.266
5(I)   -0.814
2(O)  -0.740 

6(I)    -052.9mv
7(I)    -4.266
3(O)   -0.740

10(I)   -4.266
11(I)   -1.773
14(O)  -1.768

12(I)   -0.984
13(I)   -0.774
15(O)  -0
9(O)    -4.265
VCC PINS 1 & 16 = -016.5mv
VEE PIN 8 = -5.3

PINS EMPTY SOCKET U-37

4(I)     -2.088
5(I)     -2.069
2(O)    -4.266
 
6(I)     -0.771
7(I)     -0.740
3(O)    -5.3

10(I)    -5.3
11(I)    -0   
14(O)   -0.805

12(I)    -1.805
13(I)    -1.488
15(O)   -5.3
9(O)     -0

1 VCC    -016.5mv
16 VCC  -016.5mv
8 VEE    -5.3

MarkL:
Well, that's some interesting values with U37 out of the way.

- Pins U37.3 and U37.15 are now being pulled fully to -5.3V (-5.2V nominal), which is correct.  This says the inputs they are going to on other gates are probably ok, and it was the outputs on U37.3 and U37.15 that were bad.

- Pin U37.2 should now also be pulled to -5.3V but it's not.  Output U33.9 could be bad, or there's an input on that node among the six inputs on U33 and U34 that's bad.

- It's odd that pin 11 is 0V, because that's coming from a level shifted output on U39, a 74LS109.  I would double check that, and check output U39.7.

I wouldn't put a new U37 in just yet until you're satisfied the other connected chips surrounding it are ok.  ECL outputs can sustain an absolute maximum of 50mA on outputs which is easy to exceed with a short or low impedance path to Vee.  You don't want to kill the new U37.

I think I would be tempted to pull U32 next.  U32.5 and U32.6 are both near 0V, and it seems more likely it is a C-E short on both those outputs than an identical input issue on both U33.6 and U34.6.  (This is an example of where the current tracer would help, instead of pulling the chip.)

Mick B:
Hi Mark, VERY EXPENSIVE but
I made an offer on a HP 547A current tracer Should have an answer soon.  When I was reading HP troubleshooting tools it looked like that is something to have, these chips are not fun to pull being soldered on both sides.

MarkL:
The 547A is handy for troubleshooting this era equipment, and some of these problems in particular, but certainly is not required if you don't get your bid.

For many years all I used was an Edsyn SoldaPullt for desoldering.  Any good solder sucker should pull the solder from both sides.  Sometimes you need to put more solder on for it to be effective, and applying flux can also help.  If there's excessive solder on the top side that's not melting, you could try removing the excess with solder wick first, and then proceed with the solder sucker from the bottom.

I recently purchased a Hakko FR-301 vacuum desoldering tool which does a decent job.  It's much faster when there's a lot of pins.

Mick B:
Hay, the one I bid on someone bought it outright. as I should have. O-well. I have a power vacuum sucker as well as a few manual ones. I just worry about damaging the pads. but it's never stopped me. That tracer looked like such a time saver; I will keep my eye out for a reasonable priced one for the future.
Back to the issue. I followed Pin U37.11 & U39.7
Pin U39.7 has +3.596 and get lost trying to find components do you know what that is in the photo.
What is really needed is a component locater do you have one for option 001? my manual says its located at the end of the chapter but it's not.
I'm going to remove U32 now.
I have U32 on order. nothing local.

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