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Old 25th May 2019, 6:32 am   #4
GW4FRX
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Join Date: Aug 2005
Location: Shrewsbury, Shropshire, UK.
Posts: 149
Default Re: Racal RA1772 (Ser 497) update

Quote:
Originally Posted by HamishBoxer View Post
I think Tantalum caps cause trouble on this model.
Nowhere near as much as they do on the RA1792!

Pertinent to a thread elsewhere about PVC outgassing, many RA1772s suffer from it. The main wiring harness between the mains transformer, the rear-mounted PSU board, the reservoir capacitors and the rear heatsink carrying the PSU pass transistors was executed in PVC-insulated cable which in service became very hot. Over the years this caused the plasticizer to leach out and vigorously attack any copper it could find. The result is extensive radial cracking of the insulation and corrosion of the wiring and associated terminals.

The cure is to rewire the entire harness in modern PTFE cabling, which is a chore but not inordinately difficult and allows easy replacement of the reservoir capacitors at the same time.
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