[Collins] 30S-1 relay problem

[Dr. Gerald N. Johnson]

On Sun, 2007-04-01 at 13:17 -0700, Glen Zook wrote:
> That, and cleaning the relay contacts are also good
> advice as well as reversing the contacts on the relay
> coil.  There also may be a capacitor, or two, in the
> circuit that might possibly be "healing" the longer
> the unit is on.
> 
> Glen, K9STH
> 
> On Sun, 2007-04-01 at 08:04 -0700, Glen Zook wrote:
> 
> Try reversing the DC leads to the coil of the relay.
> This will reverse the magnetic field and may overcome
> the possible problem of residual magnetism.
> 
> --- "Dr. Gerald N. Johnson" <g369n792j at ispwest.com>
> wrote:
> 
> I lean towards the gumming of the pivot lubrication
> since the problem is less after the rig is warm.
> 
I've discounted the capacitors, since they should be disc ceramics and
the voltage is low. But then there might be some inductive kick. And
that might be getting to whatever is running that circuit. At least I am
presuming that the two .01 caps, C135 and C212 (in my Yellow book
schematic) are disk ceramics and not black beauties. They are on the
ground side like the external switch and leakage there could hold the
relays in. C132 is on the power side of the input relay coil and if its
leaky its not going to hold the input relay powered. Their purpose is
only to reduce the stray RF accidentally coupled to that control circuit
and its escape from the shielded compartment. They have no time constant
or other control function. If there was an aluminum electrolytic in the
control circuits, yes it would be highly suspect, but there isn't. The
only aluminum electrolytic is the relay supply filter and if its bad the
relays will be buzzing or doing nothing at all. They won't be pulling in
to drop out slowly.

It would be a good test to see if the relays dropped out rapidly when
the cable was pulled from the Antenna Relay jack on the 30S-1 while the
exciter was in transmit mode and the 30S-1 was cool. If the relays
dropped out rapidly that would hint at exciter switching. We don't know
what that exciter is. Alternatively simply shorting a short cable
plugged into that jack and opening it listening for rapid relay
operation would be a useful test.

And while its rare, it could be that one of the disk ceramics is going
bad. Had I built the circuit, I would have included a diode on the relay
coils to cut down on inductive kick that can annoy other circuits and
contacts. I might have used 28 volt relays to cut the coil current some,
but then I'd had to included a special relay supply. The 6 volt relay is
probably drawing something above 120 milliamps.

Then there's the question of which relay is slow. If its the input relay
its auxiliary contacts control the PA tube plate current. If its the
output relay its auxiliary contacts run the input relay. 
-- 
73, Jerry, K0CQ, Technical Advisor to the CRA
All content copyright Dr. Gerald N. Johnson, electrical engineer