[time-nuts] another 5061A question

[wje]

I just did an oven rebuild on mine. It can be straightforward or not, 
depending upon what has failed.
However, if your unit locks and stays locked, the oven is most likely at 
least partially working. The VCO loop capture range is very small and it 
doesn't take a great deal of temperature variation to lose lock. Check 
your control voltage reading and monitor it over time. If that's varying 
a lot, you may have an oven issue. Mine stays within about +/- 5 of the 
setpoint.

The meter is across the series regulator for the heater. Mine starts 
pegged and drops to 46 over about 30 minutes. If you aren't seeing any 
variation, I'd suspect a problem in the oven loop control. You can 
easily take the osc out and run it on the bench. Just apply +18v to '20' 
and '24', using the case as ground. The power driver for the heater is 
on the pcb at the end of the can with the connectors. Note - be really 
careful to not connect power to the '+15' pin. This is not an input. It 
connects to a 15 v Zener in the oven cavity, which will immediately 
vaporize. Yes, I learned this the hard way.

Popular failure points seem to be the series pass transistor for the 
heater, the 4.7 ohm emitter resistor, and the fusible links for the 
proportional heater and the quick-heat heater. But, if you actually do 
have a problem, I'd be more inclined to suspect the thermistor bridge 
circuitry, which is on a pcb at the other end of the can.

Bill Ezell
----------
They said 'Windows or better'
so I used Linux.



Morris Odell wrote:
> Hi all,
>
> As I wrote the other day, I got the 5061A going again and it hasn't missed a 
> beat.
>
> One thing I have noticed though, is that the Osc Oven indication on the 
> meter doesn't change at all as  the unit warms up as the manual mentions it 
> should. It remains on 45. The unit itself is a 105-6013 and gets warm and 
> seems to function OK. Is this normal? I know these ovens have a 115V 
> preheater which might be working even if the proportional heater is not.
>
> The schematic shows that in the Osc Oven position the meter is connected 
> across the heater in series with a thermal link. Does the absence of any 
> variation mean that the heater or link is open or is the preheater keeping 
> it close enough to temp so that the heater doesn't work too hard? How hard 
> is it to open it up?
>
> Unfortunately it's back on the rack and another project is on the bench. It 
> might have to stay that way for a week or three, so there's no hurry to get 
> back into it.
>
> Cheers to all,
>
> Morris
>
>
>
>
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