Telefunken V672D Oscillating

Hi guys,

I'm having problems with oscillation on a Telefunken V672D preamp (used as a mic preamp).

There are a pair in a rack, and the second channel has recently started "motorboating" (thud...thud...thud...thud...).

The electrolytics are all original. Should I start by replacing these as they will surely be dry now, or are there any other known problem areas where I should look?

The racking job is fairly impeccable, and the general wiring, etc. looks good to me.

Cheers,

Roddy

A while ago I bought four TAB V372D. I don't know how similar they are, but there were a lot of broken electrolytics in the PSU part. Some broken transistors, too, probably as a result of dead electrolytics surrounding them. So it's probably a good idea to replace at least the electrolytics in the PSU section.

Well, I replaced all the red electrolytics as Silent:Arts suggested in this thread:

http://www.groupdiy.com/index.php?topic=14037&highlight=v672d

But it is still oscillating. Maybe I should replace the old Frako electrolytics too.

Ok, that's all the old electrolytics replaced and it is still oscillating sadly.

Any other ideas?

Hah! I replaced the only cap which was newer (it had been replaced already) and.... Voila! It works fine now.

Lucky I tried that.

Cheers, Rossi.


Roddy

:thumb: :grin:

Those electrolytics, I tell ya!
BTW. When I got my V372D units, I anticipated that the tantal caps in there had gone bad (lots of them in there), but they were fine, actually. I replaced lots of aluminum electrolytics of various brands, a few transistors and even a trim pot, but not one of those tantal caps had gone bad.