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8116A Code 42

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MarkL:
A working one - that's even better!  A working unit of anything makes a great comparison reference to fix a dead one.  Duplicate the settings and start comparing various nodes in the trouble area with either a DMM or oscilloscope, or even signature analyzer.

The scope FFT is definitely the right thing to adjust the harmonic distortion on these units.

It's always a great goal to prevent more landfill and it's why I like fixing this old equipment.  It's often a lot slower with less features than their modern counterparts, but a volt is still a volt, and great bargains can be found.  I think the only exception to that is oscilloscopes  They are such a valuable tool with ever increasing ease-of-use and analysis features, that it's worth the investment to refresh every 5 to 10 years, at least in my opinion.

I have a few things that are beyond repair, and in general I have a working version too.  I keep the dead one for parts, which also keeps it out of a landfill.  But I always make sure it's clearly labeled as broken, and I also mark the areas where I remove parts so when I look at it years later, probably for another part, I'll know what I did to it (hopefully).

Mick B:
I'm am going to give this a rest. I will be back investigating the very hot IC's Thanks for the help.
 

Mick B:
Hello MarkL been awhile, hope all is well.  I dove back into this thing with a performance test I got to the burst test and ran into problems. the burst outputs a signal but does not stop at any BUR setting. so, I thought I would go look at 10.3 troubleshooting VCO & Width Gen. it passed up to waveform selection, table 10.3-8 is there is an issue. The 1st test in the table WF2 & WF1 both L (OK) 2nd test, WF2 only L on Sq wave and WF1 only H on Sq wave. I stopped at this point not sure if I'm doing something wrong or if this is a problem and where to go next.
Settings= I.BUR, 9.99 mHz @ 1v
 

MarkL:
Given that burst mode is not working, and your U33 and U37 on the burst option board (middle board) are roasting hot, I would focus on that first.  I'm assuming this is still the case.  Not saying that there isn't something strange or possibly faulty with your results in table 10.3-8, but one problem at a time.

The burst control circuitry is ECL, which will run hot, but not around 80C that you mentioned before.  I would take a look at the power supply going to U33 and U37.  It should be -5.2V.  Since the other ECL chips are not unreasonably hot, it's probably ok.

As a cursory check, take a look at the logic level inputs and outputs on both these chips.  You should see voltages in this range for outputs, and for inputs that are not externally tied low or high:

  ECL switching levels
                  Min    Typ    Max  (mV)
                 -----  -----  -----
    output HIGH   -980   -895   -810
            LOW  -1950  -1790  -1630
    input  HIGH  -1130   -970   -810
            LOW  -1950  -1715  -1480

In particular, outputs that are very negative could be causing heating issues since ECL outputs only have an emitter follower with the collector tied to 0V.  The output could be fighting a short to -5.2V, for example.

If this is all ok, we'll need to dig deeper and verify that the logic functions implemented by the chips are ok.  I wouldn't conclude these particular chips are dead since it could be something external.

Mick B:
Hi Mark, glad you're here. After I did this, I decided to swap the A1 Board between the 2 WOW! some disassembly was required the cooling solutions were not the same, ran through a quick check the voltages spot on, over and undershoot < 4% & Rise times < 6ns. this new board is working well.
 I did not know where to set this to check ICs U33 & U37 so punted. Frequency 1K Amp 1V. EBUR mode, EBUR 3. (I'm sure I will have to do this over.) but for now.
U33 MC10104P
Pin 1. VCC -021.27
INPUTS
A pin 4. -03.1582
A      5. -01.7686
B      6. -058.474
B      7. -03.1481
Pin 8. VEE -0.5288
C     10. -0.3147
C     11. -0.8178
D     12. -0.9851
D     13. -0.7788

OUTPUTS
A pin 2. -0.7974
B      3. -0.9647
C    14. -0.7581
D    15.  000.
        ______
D      9.OUT -03.1471
Pin    8.VCC 2. -05.288
*********************************
U37 MC10103P
PIN 1. VCC 1. -020.031
INPUTS
A Pin   4. -02.716
A        5. -02.714
B        6. -0.9660
B        7. -0.7982
PIN 8 VEE -05.2925
C       12. -01.8690
C       13. -01.8310
D       10. -052889
D       11. -02.6613
              _____
C PIN   9. OUT
PIN     16 VCC2. -02.389

Temp's in IC U33 = 79.3 C and U37 = 65C Note: I have new chips
These voltages don't look good. If I tested them right.

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