[time-nuts] Anyone familiar with SR-620 repair?

[Magnus Danielson]

On 03/23/2012 07:32 PM, John Ackermann N8UR wrote:
> My SRS SR-620 counter died last weekend. After superficial
> troubleshooting, it looks like there's probably a short on one of the
> power supply rails. Symptom is that nothing lights up when power is
> turned on, but one or more of the three terminal regulators gets very,
> very hot (can't tell which one since they're all bolted to the side rail
> as heat sink). The unit had been running continuously for several weeks
> when the failure occurred.
>
> I just learned from SRS that they charge a flat rate 25% of the current
> list price for repairs! (To be fair, if you're the original purchaser,
> it's only 20%.) The SR620 currently lists for about $5K, so we're
> talking about a mighty expensive shorted cap (if that's what it is)!
>
> Anyway, has anyone here troubleshot an SR-620 with a problem like this,
> or have any general insights about working on one of these beasts?

You have several tantal caps in there. They can have short-circuit as 
failure mode. Use the schematic and PDF manual to follow up.

Make a note of which stabs/transistors over-heat and then turn off and 
try to see if any of the caps is also hot.

The design has no fold-back on over-current of the power lines.

Cheers,
Magnus