Products > Test Equipment

8116A Code 42

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Mick B:
Thanks Mark, I understand. I regret wasting any of your time, like I said just learning.
I have changed all the results to reflect, Volt's from U32 ~ U34 Starting at « Reply #70
leaving all the text the same for people reading these posts to understand that I was using the term "mv" when it should have been "V" very misleading, details matter.

MarkL:
Ok, now with the updated numbers...

Both the old and new U32 I agree look ok.  All the outputs are complements of each other and at good ECL logic levels.

Is this a new U37?

U37.15 is too low for an output, and may be the reason for the heating.  It may be getting dragged down.  As a test, you could unplug U37 and place a 100 ohm resistor to ground on U37.15.  The only other things on that node would be two inputs U36.6, U36.7 and pull-down R62.  ECL inputs are high impedance, so the inputs wouldn't matter and this test would form a voltage divider made up of 100 ohms and 470 ohms (R62).  You should get a reading of around 0.93V.  If not, one of the inputs on U36 is probably bad.

Almost all of the logic levels on U33 and U34 appear ok, meaning the outputs are consistent with the AND function, except for the output U33.9 which is not correct.

Also, the -0.7V logic HIGH tie point is measuring -0.967V, which is right on the edge of what's considered a logic HIGH.  That's something that should be investigated.

One thing at a time.  I would remove U33 and U34 and let's focus on why U37.15 is not right, as per above.  I think it's ok to leave U32 in for now.

Mick B:
OK!

--- Quote ---Is this a new U37?
--- End quote ---
Yes All chips are new.
Setting up a voltage divider brilliant.
The voltage divider  with U33 and U34 removed produced -0.96V
   

--- Quote ---Also, the -0.7V logic HIGH tie point is measuring -0.967V, which is right on the edge of what's considered a logic HIGH.  That's something that should be investigated.
--- End quote ---

Is this the common input Starting at R64?
Or is it U33.12 that's suppose to be -0.7 V but is -0.948 V with chips removed
OR I don't know what you mean. I'm sorry i'm tired a long day in the sun.

MarkL:

--- Quote from: Mick B on June 27, 2024, 02:00:00 am ---...
The voltage divider  with U33 and U34 removed produced -0.96V

--- End quote ---
Well, that value is correct, which says it's not U36.6 or U36.7 loading the output of U37.15, and it also verified the pull-down R62 is ok.

You could try the old U37 in that socket and see if you still get -2.60V on U37.15.

For comparison, my U37 is at 48.7C.
   

--- Quote ---
--- Quote ---Also, the -0.7V logic HIGH tie point is measuring -0.967V, which is right on the edge of what's considered a logic HIGH.  That's something that should be investigated.
--- End quote ---

Is this the common input Starting at R64?
Or is it U33.12 that's suppose to be -0.7 V but is -0.948 V with chips removed
OR I don't know what you mean. I'm sorry i'm tired a long day in the sun.

--- End quote ---
It's supposed to be a fixed -0.7V provided by the voltage divider R58/R65, if we can believe the schematic.

However, calculating the resulting voltage using the resistor values on the schematic, it turns out it actually results in -0.92V (or -0.94V in your case with a -5.3V supply).  Why they labeled it as -0.7V I don't know, but is probably a red herring at this point.  Placing the logic HIGH tie point so close to the threshold was not a good design choice in any case.

So let's leave that one alone for now, but keep it in mind.

Mick B:
OK Good news, I could not find the old U37. But I did find another chip from a different vendor and the results are
U37.15
Power on -1.77V
pushing the MAN button once -1.28V
pushing the 1 cycle button once -1.77V
pushing 1 cycle one more time -0.785V
and one more time and back to-1.77V
I pushed these buttons in this order right after power on. I believe I had a bad chip, It is mildly warm

I have enough 1% resistors to get -.7V  if you think that might be something to look into when this comes to and end. or leave well enough alone
Tomorrow, I will post the results of the whole chip, Put U33 & U34 back in and see  what's what

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