8116A Code 42

[MarkL]

Ok, there's a few things we should look at.

The first, as you've pointed out, is U33.6 being close to 0V.  Because this pin was changing slightly before, the pulldown for that node might be open (R62.5).  The easiest way to check is to use a 470 ohm resistor and hold it to pin 6 and Vee (pin 8 ) at the same time while watching the voltage on pin 6.  If you get a normal ECL logic level, R62.5 is open.  You can either replace resistor network R62, or just solder in a stand-alone 470R resistor underneath.  I would probably do the latter since it's easier and you can move on to other areas.

If pin 6 stays near 0V, it's likely the output on U32.5 is toast.

What is the voltage at U33.5?


On U37, three of the four outputs, pins 2, 3, and 15 are unusually low.  The fourth, pin 14, is inconclusive because it is wire-OR'd with two other gate outputs.  I am highly suspicious of U37.  The reference voltage generator in the chip is shared between the gates and it might be dead.

A possible way to check is to make the unused output, pin 9, live by connecting it to Vee through a 470R resistor.  See if you get a valid ECL logic level on pin 9.  If not, it may be time to pull U37.

If you remove U37, I'd recommend 1) put a socket in its place, and 2) check the voltages on all the pins while it's out because the isolated readings may provide clues to other problems.

I'm also noting that U37.2 is wire-OR'd with U33.9, but other sections of U33 appear to be working, which goes against the dead U37 reference generator theory.  I'm not sure what to think of that yet, but it may also indicate an issue with that gate on U33.  Measuring the pins on U37 with U37 out can tell us more.

And as with placing a 470R on U37.9, it may also be useful to make U33.15 live and get a voltage reading on that too.  (U37 and U33 pins 9 and 15 should be complements of each other.)


Another approach when there are many logic gates hanging off a single node, like in this circuit, is to use a logic pulser and current tracer combo, such as the HP 546A (adapted for ECL) and HP 547A.  These allow you to determine where the current is going.  They can be very useful with ECL with its wire-OR'd architecture, and can often lead directly to the culprit.  If you have these, let me know and we can make use of them, but they are not common.  They can be had on ebay, but they command a high premium and not worth it at the going rate, in my opinion.

[Mick B]

Hay there, I can't believe I left off pin 5 I went back and rechecked pin 6 again and lost where i was.
U33 Pin 5 is -0.814
I will do all the things you ask. I made an offer on one of those logic probes, between my son and I we have several HP devices. of this era. If he excepts, I should have it by June 6 at the latest. I would like to take this time to go through the manual and see if I can make heads or tails of these ECL circuit's I have a basic understanding, but I can do better. I an hoping by the time this HP8116A gets worked out I will have a complete understanding of this unit and how it does what it does at the circuit/component level. Thank you, Mark.

[Mick B]

Things to report. The logic probe will be here on 6/1. The voltage is up to 58mv on pin 6. and holding.
ALSO you said "On U37, three of the four outputs, pins 2, 3, and 15 are unusually low." did you meant high?
Anyway, using 470Ω  as requested produced.
U33.6       -0.085
U33.15     -0.758
 --------------------
U37.9       -3.43
 

[MarkL]

Things to report. The logic probe will be here on 6/1.

I had mentioned the HP 546A Logic Pulser and 547A Current Tracer.  There is also a thing called the HP 545A Logic Probe which is often sold with the other two, but not as useful if you already have a scope.  What is it that's on the way?

If you have not used any of these tools before, you can familiarize yourself:

  https://www.hpmemoryproject.org/an/pdf/an_163-2.pdf

The voltage is up to 58mv on pin 6. and holding.

Is that +58mV or -58mV?  If +58mV, I'm not sure where it's getting a positive voltage.  Maybe take a look at U32.7 since that signal is coming from a TTL IC with positive supplies.  And if -58mV, it's just wrong anyway since it should be between -1.75V and -0.90V (again, typical values).

ALSO you said "On U37, three of the four outputs, pins 2, 3, and 15 are unusually low." did you meant high?

No, I meant low.  Those outputs are between -3.70V and -3.13V and a typical ECL logic low is -1.75V.  I'm saying those outputs are very low compared to -1.75V (-3.13V < -1.75V).

Anyway, using 470Ω  as requested produced.
U33.6       -0.085
U33.15     -0.758
 --------------------
U37.9       -3.43

U33.6 is stubbornly staying near 0V and it shouldn't be.  The output is an emitter follower, so should be one diode drop below 0V (approx. -0.7V) at a maximum.  It could be the output driver on U32.5 is shorted.  The other half of the output, U35.2 U32.2, is connected to U33.5 which you report at -0.814V and is ok.

U33.15 is ok.

U37.9 is very low with the only thing on it being the 470R test resistor.  Again it should be in ECL logic level range.  Both of the outputs on this gate are very low and I'm not coming up with a good model (yet) of how this could be happening.


Below is a diagram of a MECL 10k OR gate, for reference on what's going on inside the chip.  Some of the other gate types are structured differently to reduce propagation time, and unfortunately those diagrams are not available so we can't make too many assumptions when considering what might have failed internally.

The diagram is from the Motorola 1989 MECL System Design Handbook, which has a detailed discussion of the circuit's bias levels and transfer characteristics.  Chapter 1 is worth reading to understand how ECL works, and what could be happening internally when things go wrong.

  http://bitsavers.trailing-edge.com/components/motorola/_dataBooks/1989_Motorola_MECL_System_Design_Handbook_4ed.pdf

EDIT: Typo - fixed reference to U32.2.

[Mick B]

Wow, Information overload I love it!
This is what I received today HP 546A Logic Pulser. I will no longer call this Logic Pulser a probe. So much reading, I downloaded both of these publications and the service manual for the HP 546A.

Is that +58mV or -58mV?

It is -0.058

No, I meant low.  Those outputs are between -3.70V and -3.13V and a typical ECL logic low is -1.75V.  I'm saying those outputs are very low compared to -1.75V (-3.13V < -1.75V).

DOH! I was looking at my numbers being higher than yours. I get it, a lower negative voltage referencing ground. I won't make that mistake again.
OK! I'm going to do a lot of reading. I will get back to you in a couple of days, also I have a couple of other things that need my attention. Thanks again.




 

[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.

[MarkL]

That yellow component is a resistor network.  The "59" next to it means R59, and 1810-0243 is the part number that you can also look up in the parts list.

I never noticed that the Option 001 parts locator was missing from my PDF service manual too.  I have a printed version of the service manual and scanned in that page, attached.

[Mick B]

WOW!, thank you for the missing pages, I suspected that was R59 but wasn't sure where R61 was the way the chips jump around. Really helpful. 
  I'm supposed to have the MC10101P ICs by the 17th. I pulled U32 and took voltage readings
U32 EMPTY SOCKET.
U33 CHIP IS STILL IN.
U34 CHIP IS STILL IN.
U37 EMPTY SOCKIT.

U32 Pins
1 & 16 VCC =010.9mv

2(O)    -5.134
4(I)     -2.080
5(O)    -052.12mv

3.(O)     -5.315
6.(O)     -048.63mv
7. (I)     -021.93mv

9.(O)     -1.173
13.(I)    -1.806
15.(O)   -0

10.(I)    -023.44mv
11.(O)   -5.316
14.(O)   -4.515
12.Common Input -5.318


U33 pins
1 & 16 VCC= .014.59mv

4.(I)    -4.380
5.(I)    -5.310
2.(O)   -.752mv

6.(I)    -051.19mv
7.(O)   -4.378
3.(O)   -.772mv

10.(I)   -4.378
11.(I)   -4.517 
14.(O)  -1.771

12.(I)   -1.075
13.(I)   -1.771
  9.(O)  -4.378
15.(O)  -0
8. VEE  -5.314

Pins U34
1 &16. VCC -014.384mv

4.(I)   -4.376
5.(I)   -5.315
2.(O)   -.790mv

6.(I)    -0.475mv
7.(I)    -4.375
3.(O)   -.820mv

10.(I)   -4.375
11.(I)   -5.316
14.(O)  -1.807
 
12.(I)   -1.075
13.(I)   -.778mv
  9.(O)  -1.806
15.(O)  -0
8. VEE  -5.314

Pins U37
1 &16. VCC -013.72mv

4.(I)   -2.091
5.(I)   -2.071
2.(O)  -4.377

6.(I)   -.771mv
7.(I)   -.751mv
3.(O)   -5.311

12.(I)   -1.806
13.(I)   -1.431
15.(O)  -5.317
  9.(O)   -0

10.(I)    -5.315
11.(I)    -2.088
14.(O)   -1.172
8. VEE    -5.315
 
NOTE:   You asked check U39.7. It has +3.596v
And the temp on U33 is 70C Still.



 

[Mick B]

Notice the voltage on U37.11 @-2.08 there is an intermittent problem also the BUR light. I don't know what the problem is YET but sometimes when turning on, the voltage is missing from pin 11 and not at the same time as the BUR light. I will poke around and see if I can't narrow this down oh ya I can get the voltage up on pin 11 by messing with the mode switch (EBUR)

OK, it seems turning it on when in EBUR mode after being off for a min or so there is no voltage on pin U37.11
Pushing lower left buttons. Pos slope trigger, MAN, 1 Cycle will turn on -2.08v @ pin11 on U37. as well as the EBUR mode button.
I can't get the BUR light to mess up again.

[Mick B]

Good afternoon, The MC10101P (U32) chips have arrived, I have a JBL amp on my bench. I will get back into the HP 8116A tomorrow for those following along. Looking forward to your input Mark.

[MarkL]

I've been out traveling for the last week.  Will review your latest readings and post some suggestions for next steps in the next day or two...  sorry for the delay.

[Mick B]

I've been out traveling for the last week.  Will review your latest readings and post some suggestions for next steps in the next day or two...  sorry for the delay.

Hope your journeys went well, Glad your back. I have since removed U33 also, measuring U32 with U33 missing
U32 OUTPUT PINS
  2.  -5.3 V
  5.  -5.3 V
  3.  -5.3 V
  6.  -039.53 V
14.  -5.3 V
11.  -5.3 V
15.  -0 V
  9.  -0.833 V

U32 INPUT PINS
12.  -5.3 V
  4.  -2.08 V
  7.  -010.00 V
10.  - 010.67 V
13.  -1.81 V

U34B PINS
  6. (I)  -038 .31 V
  7. (I)  -5.07 V
  3. (O) -0.828 V
 

[MarkL]

Ok, some interesting observations...

With U32 out of the way, inputs U33.6 and U34.6 should both be -5.3V (-5.2V nominal), but are still close to 0V.  There's nothing else connected to these nodes, except the pull-down resistors (R62) which is what should be pulling them to -5.3V.  As an example, both U33.5 and U34.5 are now at -5.3V, which is what should be happening.

One additional verification you could perform is to hold a 470 ohm resistor to each of the pins U33.6 and U34.6 to see if they go to -5.3V.  Maybe the pulldown resistors are bad, but it's unlikely since you did this test before with U32 in-circuit.  If they stay near 0V with the resistor test, I think we can conclude both U33 and U34 are bad, at least on that gate.  It's odd that it's the same gate on both.

U33.11 is at -4.5V, but should also be at -5.3V with nothing else on that node.

And more... U33.4 and U33.5 are both logic low, yet the output for that gate on U33.2 is high.  This is wrong.  Same for U34.4 and U34.5.

With U37 out, U33.9 should be closer to an ECL logic level, but is not.  Again implicating U33.

U37.14 should be an ECL logic level, but is somewhere in-between.  This node is not involved with U33 or U34, but it is wire-OR'd with other outputs U35.3, U35.15, U32.9 (out), and inputs U203.10, U32.13 (out), U38.7.  Might need further investigation.


Ok, now read your next post about removing U33...

So now U32.5 is where it should be at -5.3V with U33 gone.  U33.6 was holding that node high, which it shouldn't be.  That input must be shorted high internally (probably base to collector short on the input transistor).

U33.11 is also good now at -5.3V (was -4.5V).  Maybe caused by some reverse emitter to base leakage caused by the overly high voltage on U33.6, but notably not present on U33.5,  But doesn't matter, clearly U33 needs replacing.

I would suspect removing U34 would do the same for U32.6, which would say U34 is dead too.

Obviously no need to do the 470 ohm resistor test described above, since removing U33 proved the pull-down resistor is working.

[Mick B]

Hello there Mark, that is the conclusion I came to also with U34.6, I bought extra chips just in case I will get to removing it. and post the results tonight.

[Mick B]

OK, U34 removed, U32.6 & U34.6 are -5.3 
when plugging in new chips should I do U32 last? (also some of these are Ebay chips of unknown quality)
What do you think Mark?

[MarkL]

I don't think the order is critical and I haven't seen anything to make me think the new chips are in danger, but I would definitely do it one at a time and check for nonsensical logic levels as you go.

Did you install sockets?

I think it would be mildly interesting to plug in the old U32 first and see if you get the expected outputs on it now.  As per the previous observations, one of the main problems with the nodes near 0V was either with U33+U34 or U32, and we've concluded now it was U33+U34.  So, U32 might be ok and it would be interesting to know.

[Mick B]

Hello, Yes I used socket's here are the U32 readings no other chips in, old chip and new chip
U32 OLD
  PINS........Note: not very warmed up
  2.  -0.817 V
  5.  -1.77 V
  3.  -1.78 V
  6.  -0.817 V
14.  -1.77 V
11.  -0.817 V
15.  -0 V
  9.  -0.834 V

U32 NEW.....Very warmed up
  PINS
  2.  -0.766 V
  5.  -1.72 V
  3.  -1.86 V
  6.  -0.778 V
14.  -1.86 V
11.  -0.775 V
15.  -0 V
  9.  -0.832 V

It looks like U32 was OK. 

Going to start adding chips starting with U37.....U33.....and lastly U34

[Mick B]

OK, starting with U37 the temp is 68.4C still very hot ay?
  U37
  4. (I)  -2.23 V
  5. (I)  -2.22 V
  2. (O) -1.67 V

  6. (I)  -1.84 V
  7. (I)  -1.82 V
  3. (O) -1.79 V

10. (I)  -5.29 V
11. (I)  -1.89 V
14. (O) -0.765 V

12. (I)  -1.83 V
13. (I)  -1.78 V
15. (O)  -2.60 V
  9. (O)  -0 V

   U33
  4. (I)  -1.66 V
  5. (I)  -0.767 V
  2. (O) -1.82 V

  6. (I)  -1.71 V
  7. (I)  -1.66 V
  3. (O) -1.84 V

10. (I)  -1.66 V
11. (I)  -1.85 V
14. (O) -1.85 V

12. (I)  -0.967 V
13. (I)  -1.75 V
15. (O) -0 V
  9. (O) -1.66 V

    U34
  4. (I)  -1.66 V
  5. (I)  -1.85 V
  2. (O) -1.83 V

  6. (I)  -0.779 V
  7. (I)  -1.66 V
  3. (O) -1.85 V

19. (I)  -1.66 V
11. (I)  -0.775 V
14. (O) -1.84 V

12. (I)  -0.967 V
13. (I)  -0.825 V
15. (O) -0 V
  9. (O) -1.83 V

Now, I had the settings at MODE= EBUR @14, AMP =1V, offset = 0V, FRQ = 1KHz, WAVE =OFF, Output = ON.
Some of the voltages are different than you known good ones but still in range, I wonder about settings?
Also I don't have anything to compare U34 with.
It's getting late, I'm going to bed. Thank you.
 

[MarkL]

Hello, Yes I used socket's here are the U32 readings no other chips in, old chip and new chip
U32 OLD
  PINS........Note: not very warmed up
  2.  -0.817mv
  5.  -1.77
  3.  -1.78
  6.  -0.817mv
14.  -1.77
11.  -0.817mv
15.  -0
  9.  -0834mv

U32 NEW.....Very warmed up
  PINS
  2.  -0.766mv
  5.  -1.72
  3.  -1.86
  6.  -0.778mv
14.  -1.86
11.  -0.775mv
15.  -0
  9.  -0.832mv

It looks like U32 was OK. 

Going to start adding chips starting with U37.....U33.....and lastly U34

Did you really mean mV on the above readings, or V?  If mV, there are some major issues.

And the next set as well.  Please clarify before I start analyzing anything.

[Mick B]

Did you really mean mV on the above readings, or V?  If mV, there are some major issues.
[/quote]

1.The readings are Volts example -1.77......is this not - 1,volt and  770 millivolts?
2.The readings are in Millivolts example 0.817mv........ is this not -800 and 17 millivolts?   
I wrote these I thought as to avoid confusion I guess this is wrong
Please tell me the correct way, and I will do that way every time.
Is there a problem with U32?  I thought the readings were because of the settings in EBUR controlling the output?
Time to regroup.  Please remember, I'm a beginner with some cool diagnostic equipment and the GREATEST desire to learn while I still can, @ 71
I really appreciate your time and patience with me Mark. 

PS just noticed the decimal point missing in  U32 OLD pin 9. I fixed this

[MarkL]

1.The readings are Volts example -1.77......is this not - 1,volt and  770 millivolts?

Yes.

2.The readings are in Millivolts example 0.817mv........ is this not -800 and 17 millivolts?   

No.  -0.817mV (and it's a capital V), is -0.000817V.  Which is why I was analyzing many of these issues as a shorted node close to 0V.  I don't how many wrong assumptions and conclusions were made now, and time wasted.

I cannot help you if you don't provide accurate information represented in a standard format.  Please correct your readings starting with U32 and I will look at them again when I get  a chance, and we'll start again from there.  Put everything in Volts for the purposes of measuring these nodes.  The above example should be "-0.817V" (or "-0.817 V" if you prefer a space for readability), if that's the value you meant.

  https://www.electronicsteaching.com/Electronics/units.html

  https://en.wikipedia.org/wiki/International_System_of_Units