[time-nuts] PRS10 case temperature

[Scott Mace via time-nuts]

I have been experimenting with a PRS10 and using Lady Heather to collect data. This unit had several failed components in the lamp
assembly, which I replaced and the unit locks well now. One thing I noticed is that on cold startup, the unit seems to think it's
already at 40-50C, when in reality it's only slightly above room temperature. The sensor settles around 79-82C. I've measured the
baseplate and it is around 50C. I believe that all of the ovens are running slightly low as a result (if I understand the circuit
correctly). I'm thinking that the case temp sensor, a LM45C, on the power supply board is bad. Anyone else running a PRS10 with
reasonably correct baseplate temperatures?

Here are some of the numbers I'm seeing:

AD1 - Heater supply : 24.360V
AD2 - +24V supply: 24.370V
AD3 - Lamp FET drain: 4.910V
AD4 - Lamp FET gate: 4.080V
AD5 - OCXO heater: 1.811V
AD6 - Cell heater: 2.101V
AD7 - Lamp heater: 1.513V
AD8 - Photo signal: 3.831
AD9 - I/V converter: 4.804V
AD10 - Case temperature: 80.80 C
^^^^
AD11 - XTAL thermistors: 0.961
AD12 - Cell thermistors: 0.971
AD13 - Lamp thermistors: 0.972
AD14 - Freq cal pot: 2.337
AD15 - Analog ground: 0.005V
AD16 - TXCO varactor: 7.240V
AD17 - VCO varactor: 11.520V
AD18 - Multiplier gain: 11.520V
AD19 - RF synth lock: 4.900V



Scott

[Mark Sims]

My case temp runs around 70C with the SRS heatsink installed. If you don't have a heatsink (a rather bad idea) it might run 80C. The latest SRS heatsinks don't seem to be as good as the earlier units which had a lot more metal to them... my heatsink is the later model.
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[Dana Whitlow]

My PRS-10 (a telecom version) runs with a heatsink temp of around 55C of
a bit less. But some areas of the case actually run a few deg hotter than
that.

Dana

Post by Mark Sims
My case temp runs around 70C with the SRS heatsink installed. If you
don't have a heatsink (a rather bad idea) it might run 80C. The latest SRS
heatsinks don't seem to be as good as the earlier units which had a lot
more metal to them... my heatsink is the later model.
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[Scott Mace via time-nuts]

I placed a large fan in front of the heat sink and it only cooled it down to 69C according to the case temp sensor. There's no way
the case is actually anywhere close to that temp, it's maybe 40C with that fan running. I'll replace the LM45C and see what happens.

Scott

Post by Dana Whitlow
My PRS-10 (a telecom version) runs with a heatsink temp of around 55C of
a bit less. But some areas of the case actually run a few deg hotter than
that.
Dana

Post by Mark Sims
My case temp runs around 70C with the SRS heatsink installed. If you
don't have a heatsink (a rather bad idea) it might run 80C. The latest SRS
heatsinks don't seem to be as good as the earlier units which had a lot
more metal to them... my heatsink is the later model.
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[Shaun Merrigan]

This post might be inappropriate. Click to display it.

[Mark Sims]

The case temperature derived from the ADC reading does not match actual measured values. The PRS10 data sheet says it is roughly the temperature midway between the baseplate and lamp temps.
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[Scott Mace via time-nuts]

I think I figured out the problem. When I rebuilt the lamp assembly, the R901 air heater resistor was listed as a 750ohm 2W on the
schematic so that's what I installed. I just measured the old resistor, which had a broken lead, and it is 534ohms. I sort of
repaired the broken lead and installed it. Now the unit locks up real quick and the AD10 sensor is showing around 70C. The other
problems were a broken C904 and a bad U800 8V regulator.

Scott

Post by Mark Sims
The case temperature derived from the ADC reading does not match actual measured values. The PRS10 data sheet says it is roughly the temperature midway between the baseplate and lamp temps.
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[Chris Burford]

I see a 42C baseplate temp on my PRS10. I have the newer (U-shaped) heatsink attached. I also have a 70mm fan moving air at a low speed across the the long axis of the heatsink.

The case temp (ad10) as seen by RbMon is generally 67.2C

Chris

Post by Scott Mace via time-nuts
I have been experimenting with a PRS10 and using Lady Heather to collect data. This unit had several failed components in the lamp
assembly, which I replaced and the unit locks well now. One thing I noticed is that on cold startup, the unit seems to think it's
already at 40-50C, when in reality it's only slightly above room temperature. The sensor settles around 79-82C. I've measured the
baseplate and it is around 50C. I believe that all of the ovens are running slightly low as a result (if I understand the circuit
correctly). I'm thinking that the case temp sensor, a LM45C, on the power supply board is bad. Anyone else running a PRS10 with
reasonably correct baseplate temperatures?
AD1 - Heater supply : 24.360V
AD2 - +24V supply: 24.370V
AD3 - Lamp FET drain: 4.910V
AD4 - Lamp FET gate: 4.080V
AD5 - OCXO heater: 1.811V
AD6 - Cell heater: 2.101V
AD7 - Lamp heater: 1.513V
AD8 - Photo signal: 3.831
AD9 - I/V converter: 4.804V
AD10 - Case temperature: 80.80 C
^^^^
AD11 - XTAL thermistors: 0.961
AD12 - Cell thermistors: 0.971
AD13 - Lamp thermistors: 0.972
AD14 - Freq cal pot: 2.337
AD15 - Analog ground: 0.005V
AD16 - TXCO varactor: 7.240V
AD17 - VCO varactor: 11.520V
AD18 - Multiplier gain: 11.520V
AD19 - RF synth lock: 4.900V
Scott