Electronics > Repair
Understanding and Repairing Clock Generator on Adret 742A UHF Generator
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PerArdua:
Thanks for both of your replies - I am certainly going to keep working at this. :)

I'll replace all tantalums I see, and will get to work on aluminium electrolytics too. Thus far I have been replacing the tants with 25V rated components, they are slightly larger but fit easily. Does anyone know if the attenuator assembly has any capacitors in it? I tried removing it last night but could figure how to remove it from the instrument. I removed the nut retaining the N connector from the front of the instrument, the SMA input, and four hex bolts sitting below the VHF module - are there any extra screws somewhere? Aside from that I'm comfortable with accessing the rest of the instrument (though I might try and keep repairs to the VHF module on the component side so I don't have to deal with all the feedthroughs etc).
George Edmonds:
Hi Per Ardua

I cannot immediately find a schematic for the 740 attenuator, but I have looked at the one for the 730, there is only one possible tant and that is a 4.7uf 35V one, it is in the RPP circuit directly on the 15v supply rail, so probably no problem

G Edmonds
timeandfrequency:
Hi Per Ardua,

I had an in-deep look in other Adret technical paper documentation (in that case for the 740A; 0. to 1120 MHz RF Generator) and could not find much infomation about the step-attenuator assembly.
It is only mentionned on the bloc diagram (see attached picture) ans seems to be controlled via the approach board. But globally the ouput scheme of the 740A seems to be different to the 742A you own, so unfortunately, not much infomation can be gained this way.


I'll resume searching and update if I can find something useful.
George Edmonds:
Hi

Look at the 730A information it may be the same

G Edmonds
PerArdua:
Thanks all - in that case I shall leave the attenuator assembly as is - I can't figure how to remove it and if there's unlikely to be a dodgy capacitor in there then why risk damage.

I spent this evening taking pictures of the PCBs, which I will resize and upload here in short order.

I've also started creating a shopping list of tantalum capacitors, minimum voltage rating of 25V.

For rectifier diodes - would the 6A4-TP be good candidate? Key specs: Vf - 0.95V, If(av) - 6.0A, Ifsm - 400A (https://media.digikey.com/pdf/Data%20Sheets/Micro%20Commercial%20PDFs/6A05-6A10.pdf)

Best wishes,  :-+
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