Products > Test Equipment
8116A Code 42
Mick B:
Where to start? this is a half-ass calibration. It went through the procedure up until Pg.9-11 step 7. any width parameter higher than 984 turns on the error light. I putzed around after that. I still have voltage issues and the wave forms start to lose their shape around 7MHz. apparently, there is settings after the Power Supply Preliminary because from Pg.9-3 to 9-7 all to voltages are good up to 16+ volts the and the rise times are < 6.6 but fluctuate a lot. Pg. 9-7 step has to be a misprint. these settings put the signal off the top and out of sight. And then the voltages turnout low?
These are the voltage readings from Amplitude & Offset Performance Test. Pg.8-9 Just posting my results. in The Updating Chapter Pg. 8. there is an update for Offset voltages, & DC Output. Unfortunately, these won't help my readings.
8v =
RMS
Sine 2.72v
Trangle 2.23v
Square 3.70v
3v =
Sine 1.036v
Trangle 0.862v
Square 1.425v
1v =
Sine 0.344v
Trangle 0.299v
Square 0.494v
100 mv =
Sine 034.26mv
Trangle 029.78mv
Square 049.14mv
OFFSET
@ 100mv
7.50v =7.46v
5.0v =4.97v
3.0v =2.98v
1.0v =0.957v
100mv =090.8
@10mv
795mv =0.719mv
500mv =0.453mv
100mv =092.4mv
Frequency Performance Test Pg.8-2
50MHz = 50.047MHz
10MHz = 10.086MHz
10kHz = 10.082
1kHz = 998.8Hz
DUTY %
1Hz @ 10% =9.28%. @50%. =47.68%. @90%. =89.02%.
1kHz @ 10% =10.104%. @50%. =49.97%. @90%. =89.87%.
9.99MHz @ 20%. =20.00%. @50%. =50.18%. @80%. =80.00%.
Mark where do you think I should measure first? to take static measurements with the heatsinks on?? if you can pinpoint what nodes we might want to look at I will take a picture of the backside of the board remove the heatsinks and use a bright light to find the nodes on the backside and mark them on the photo so I can find them how did you measure yours?
MarkL:
On width >984us errors, the test frequency is supposed to be 900Hz. Are you getting that on the output? Check that you have the proper voltages on the width controller IC U300, page 10.3-17. On my unit the error light turns on at 1.10ms. I'm not very familiar with the operation of U300, but the manual says error is asserted when the next trigger happens before a pulse cycle is complete. So, my guess is that something is off with the duration of the pulse high, low, or repetition rate (frequency) that is making the cycle last too long.
On the poor looking waveforms >7Mhz, keep in mind the transition time of the square wave is 6.6ns or a little less. In this unit, transition time is a constant since it's a limitation of (at least) the output amplifier. As the square wave gets higher in frequency, the transition time will consume more and more of a waveform cycle. By the time you reach 50MHz, the transition time will dominate and the waveform will look almost like a sine wave.
In terms of measuring, I did a lot of mine from the back when the heatsinks were in the way, and I used a flashlight from the top side to cast a shadow to verify I was probing the right pad underneath. On some of the probe points, sometimes you can find a resistor or diode lead that's the same node and you can measure from the top.
Also keep in mind this unit is essentially an analog function generator that has a microprocessor instead of knobs. Many of the adjustments are just calibrating the digital display to analog voltages that control frequency, amplitude, pulses, etc. Because the it's all analog, don't expect precise output for anything like you would on an arbitrary or synthesized waveform generator.
This last set of waveforms you posted are not so bad for the 8116A, but the square wave could be flatter on the bottom, and the triangle is looking a little non-linear on the downward slope. Again, maybe the crossover distortion is still getting you.
Mick B:
Thanks Mark, your help has been invaluable. I was testing the WID settings at 900Hz and @ 100us I got 102 on the counter, but the next setting @ 900us. turned on the error light and like I said it goes out when lowering the setting to 984us turns off the error light I saw -5.3v on pin 9 of U300. I tried hooking up the HP 5005A just because, changing the bridge [W3] to test and changing the jumper to FreeRun turns on the error, STA, DTY, mV and lol lights. It seems locked up, no buttons do anything, having never done this before I don't know what it supposed to do, reset does nothing hooking, up the 5005A does nothing either. where do we want to precede from here?
MarkL:
To answer your questions...
More explicitly, I was asking how your waveforms compared with the troubleshooting procedure on 10.3-17, not just the voltage on the error signal. It's fairly certain that the error output on U300 was being asserted correctly.
Free-run mode puts the processor in a tight loop executing a single instruction while incrementing the memory address lines. The unit does not boot into any operational mode, nor does it even get to any initialization code for the display. The display is just showing whatever state the latches powered up in.
Because the address lines are incrementing, it allows you to use a signature analyzer to verify ROMs, decode logic, and sometimes other areas that operate independently of the firmware (like the keyboard scan in this unit).
What do I think from here?... I would go back to the tenet of one thing at a time and finish with the output amplifier repair. You still have some unexplained crossover distortion, as last reported. Something is still not right.
I would go through the adjustment procedure and try to adjust everything having to do with output signal quality: voltage levels, linearity, distortion, overshoot, etc. If you can't get the pulse adjustments right, or some of the other timings right, skip them for now.
After adjusting what you can, if there's still crossover distortion, compare your quiescent voltages with what I posted from a working unit. I would look for voltages that are unbalanced between the top and bottom drivers in all stages. If that doesn't turn up anything, output a sine wave and try to find a frequency where the distortion is the worst, and take a look at the waveform along the heavy lines (signal path) shown in the schematic. Again look for a stage where distortion starts to be introduced, or possibly where it changes (like it's inverted). Because this amplifier has feedback, keep in mind the feedback is trying to compensate for distortion problems, so you might see some nodes that look distorted but it's actually the correction from the feedback.
And double-check the input of the amplifier to make sure the signal going into it is distortion-free.
If you were able to adjust out the crossover distortion, then great, you can try to get the pulse output adjusted properly and pick up with the troubleshooting procedure on 10.3-17 (U300).
Mick B:
MarkL, I'm back at it, I have been tied up working on the SAAB, Well the Chinese Tech2 Scanner mostly. To the 8116A, as it became apparent that the CAL was just not going well and seemed pointless so many things would not adjust to specs. and I knew it had mismatched transistors. I replaced Q502 with what is supposed to be a direct replacement A (2N5771) to complement Q501 A (2N2369A) Note: this is a TO-18 package and the 2N5771 is a TO-92. I found some heatsinks that slip on the TO-92 Package. Also, as the manual says if the waveform is distorted on the leading edge look at Q503 and Q505 and Q506 and Q505 have already been replaced so I replaced Q503 with a 2N3094 and Q504 with a 2N3906. It was a bitch doing this with the heatsinks, and the other things in the way.
The GOOD NEWS, every adjustment up until the last step (7) of OFFSET ADJUSTMENT Pg.918 dialed right in even fixed the error light in the width adjustment problem.
Step 7 says if any offset adjustments were required (a very small one) repeat the "Overshoot & Transition Time Adjustment" procedure before continuing. I went back to that chapter and the overshoot was wacked I decided to reboot the 8116A and when it came on E-51 greeted me. :palm:
I Printed out MarkL's known good readings again. I'm thinking one of the new transistors / HEATSINK. I'm not ruling out a solder joint These were ridiculously hard to solder.
We will see. I was just so happy; it was adjusting out like it was new. Voltage reading forth coming. My memory cards from England showed up and I'm expecting a new VCI module for my scanner, the wife's car takes president.
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