| Electronics > Repair |
| Fluke/Philips PM3384a combiscope digital trace faults |
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| Guineafowl21:
Hi all, In analogue mode, the CAL signal displays fine on all four channels. In digital mode, channels 1 and 3 display the trace off the top of the screen, while 2 and 4 display it off the bottom. Occasionally, the trace wobbles into view, and is distorted, lots of roll-off etc. The self tests all pass, but the autocal gets stuck after 3 minutes or so. I have the service manual, but can’t make head nor tail of the DAC repair tool function described near the end. Is there a firmware update? Anyone else had this fault? I found a thread on this forum describing something similar, but can’t find it again and anyway it didn’t really conclude. I gather a user called HighVoltage may be able to help. Cheers for now. |
| Guineafowl21:
Quick update: For whatever reason, all the digital traces are now below the screen. Also, the autocal does complete, but takes about 10 minutes (should be 4) and ends with a message to repeat the process. Status display says ‘calibration error 101’. |
| Guineafowl21:
I’ve traced the signal from the front end, and it makes it onto the digital board (using square CAL wave as test signal). It goes through a buffer/splitter OK, then through the MASPU (main aquisition signal processing unit). From there, it reaches an upright, brown-coated hybrid chip pins 1 and 2. The output is on pin 3. The wave is still there, but looks distorted. I’m not sure if this is my measurement technique, though. This then goes to a heat-sinked flash ADC. No data emerges, but I’m not experienced in this digital stuff. The power supply appears to be GND and -5V, so I expect the data to be a fast 0 to -5V signal. Perhaps someone might be able to suggest what signal to be expected at each stage? Should I be using a simpler, DC signal to trace? |
| Guineafowl21:
Anyone? Bueller? Anyone? The signal from the hybrid to the flash ADC is at -5.4V, when it should be -0.5V. If I bias it to the correct level with a suitable resistor, a trace appears on the screen. However, something’s now happened and the scope won’t trigger in analogue mode. What might I have done? |
| HighVoltage:
--- Quote from: Guineafowl21 on July 01, 2019, 01:45:42 pm --- From there, it reaches an upright, brown-coated hybrid chip pins 1 and 2. The output is on pin 3. The wave is still there, but looks distorted. I’m not sure if this is my measurement technique, though. --- End quote --- Most likely your "brown coated hybrid chip" is the culprit. Show us some pictures |
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