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8116A Code 42

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MarkL:
Regarding your description of "fluctuations", it appears you are getting readings that are unstable in the mV in most cases.  It could be noise or possibly a low level oscillation, but you are not seeing anything on your scope.  I'm going to assume for the moment the digits you've shown are stable and valid, and ignore any digits with a "?".

One thing to try is to set your DMM on AC and see what kind of readings you get on some of these nodes that are unstable.  This will block the DC and show just the varying part of the voltage on that node (within the frequency limits of your DMM).

As far as the latest updated measurements, there are several items of note:

1) Q506 B-E junction is significantly more than 0.7V (approx. 3.2V).  This would indicate Q506 B-E is open.  I would remove Q506 and check it out of circuit.

2) Q505 is off, as indicated by the B-E voltage of only about 0.4V.  The collector is therefore floating, and free to wander around (within the bounds imposed by other circuit components attached to it, such as other transistor junctions).  Even connecting your probe to the collector could be influencing the reading.  This could be the reason for the unstable readings.

3) Both Q510 and Q512 also have B-E junctions > 0.7V (approx. 0.9V to 1.0V).  Recall that they are in parallel, and this would indicate neither is working.  I would remove them both and test out of circuit.

I would try to correct #1 first and leave #3 alone for the moment.  Let's find out why Q506 is not reading correctly, fix it, and then move on.  Taking a shot-gun approach and changing multiple things at the same time creates too many variables.

You stated in the beginning that you replaced a large number of transistors.  When checking Q506 out of circuit, make sure it is the right type, PNP or NPN.  You might also want to purchase a transistor tester, as it will identify the transistor type, the pinout, and other important parameters like gain (hFE) and leakage.

For reference, my Q505.E is +22.6483V and Q506.E is -22.5548V.

Mick B:
I pulled Q506 and sure enough it was toast! Q506 & Q505 have the heatsinks on but not the cross bar they got very hot, can you tell me what your temps are for these transistor's before I move on. and the good news NO CODE!
Note: the settings were as you recommended, also all the pots on the main board are centered.
Thanks

MarkL:

--- Quote from: Mick B on February 24, 2024, 12:01:42 pm ---I pulled Q506 and sure enough it was toast! Q506 & Q505 have the heatsinks on but not the cross bar they got very hot, can you tell me what your temps are for these transistor's before I move on. and the good news NO CODE!
Note: the settings were as you recommended, also all the pots on the main board are centered.
Thanks

--- End quote ---
So, have you replaced Q506 and it now has no error code, or do you mean there is no error code with it out?

My calculations for my Q506 show that it's dissipating about 0.6W when quiescent.  Without a heatsink on such a small part I could see why it's getting quite hot.  I wouldn't run it that way for longer than what's needed to get a very quick check done, maybe less than a minute or so.  The Q505/Q506 heatsink temperature on my unit after a 15 minute warm-up is 60C.  With the case open there's not much airflow directed across it.

How did all the pots get centered?  Were they that way or did you do that?

Mick B:
Ok I replaced Q506 fired it up and error code 42 is gone. I put the heatsinks on. It still has some issues, I'm doing a rough calibration on it so far it is doing ok, those 2 IC are still blazing hot. The pots were centered by the guy I got it from, He was going to calibrate it that's when he dropped the screwdriver in it, and why I ended up with it. Just going to try and get it in the ballpark before the next big dive. Unless you (MARKL) think I should start else ware in this endeavor. Thanks   

MarkL:
Centering of all the pots by the former owner was not a great move.  I can say from experience these units can be a real bear to align.  Some of the pots are way too sensitive, i.e. a small movement can radically change parameters, and there is interplay among some that can be difficult to optimize.  It's much easier to start where it's almost right, and then tweak whatever is necessary.  Oh well.

At this point, if something isn't working right, it would be more difficult to say if there was another bad component or an adjustment that's way out.  I agree you should try to get through the adjustment procedure.

On the hot chips, you mentioned they were on the option 001 A2 board.  On page 8-20 of the service manual, there is a short verification procedure for option 001.  See if it passes.

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