| Electronics > Repair |
| Understanding and Repairing Clock Generator on Adret 742A UHF Generator |
| << < (9/10) > >> |
| George Edmonds:
Hi Email failed. I have uploaded the 740A Zip file to the files area on Marconi-Test-Instruments@groups.io. It is in a folder called Adret 740A and is some 25MB G Edmonds |
| PerArdua:
Thank you George - I've downloaded the Zip. :-+ |
| PerArdua:
Apologies for the lack of update for a while - work as been pretty intense and will likely be so for the next few weeks as I change posting. Good news though, in that all tantalum capacitors have been replaced with at least 25V or more rated components, and I have a fresh set of aluminium electrolytics on order from Digikey this week for the power supply! I will make some time this weekend to give a proper update and share some more images. :) |
| PerArdua:
Update - some good some bad, I've replaced all tantalum capacitors, as well as the four big aluminium caps on the power supply rails. When I switch on the instrument, it appears to be stable - no fires, or burning just yet. :) All tantalums were replaced with at 25V rated tantalums, the 10000uF, 25V capacitors replaced with 10000uF 35V capacitors, and the 6800uF 40V capacitors replaced with 6800uF 50V capacitors - all from Digikey. I couldn't find any that had the right pitch and sized screws, so had to resort to soldering in replacements. However, the power supply seems to be starting itself. When applying AC mains in standby, the fan turns on and the following voltages are measure: +15V: 1.33V -15V: -11.10V +5V: -0.47V +15V pilot: 6.22V +5Vfloat: -0.77V When I turn the instrument on from the front panel, a 'random' assortment of LEDs illuminate, as well as maybe 1 or 2 characters on the seven segment displays. The voltages become: +15V: 4.2V -15V: -15.0V +5V: 4.2V +15V pilot: 5.6V +5Vfloat: 5.2V It is a bit concerning to see these voltages and the PSU behaving incorrectly. However, I take some solice in the seven segment display showing a correct character - perhaps this indicates that at least part of the ROMs are be ok assuming higher probably for a legible character to appear, rather than a random assortment of segments. I plan to disconnect the PSU from the backplane tomorrow, and see if it produces sensible voltages that match those which I measured in an earlier post. In the meantime, please enjoy a few snaps from the current configuration: |
| George Edmonds:
Hi Per Ardua It is some four years since I last had to re capacitor an Adret power supply, even then I had to use snap in capacitors and solder them in. Screw fixing ones were available at a stupid price but were of a much lower spec than the snap in ones so the use of snap in capacitors became a no brainer. With what you are seeing with the power supply voltages my first reaction would be to check the continuity of all of the 0V/ground connections between the PSU board and the rest of the instrument given the crap connectors that Ardet used. G Edmonds |
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