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Old 23rd Jan 2022, 12:05 pm   #1
WME_bill
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Default Solartron 7065-7055 voltmeter PSU

I have been asked by Ziginox from Idaho for information upon the power supply of a Guildline 9575 voltmeter, which he says is identical to the early Solartron 7055 voltmeter. Apparently the manual on BAMA is a much later version.
Uses a switching regulator, which I always hate working upon. So I wish him well. I attach the circuit diagrams, part list and setting up instructions as they may prove helpful to others.
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Old 23rd Jan 2022, 11:30 pm   #2
Ziginox
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Default Re: Solartron 7065-7055 voltmeter PSU

Thank you so much, the component list matches what I found on the power supply PCB perfectly!
And yep, once you get past the Guildline stamp on the front, everything inside has a Schlumberger logo printed on it. Even the rear panel does nothing to hide it!

Of note, the Guildline 9576 also has an equivalent, the Schlumberger Solartron 7056
(Hopefully that'll help the search engines direct anybody else needing help with these instruments)

Thank you again, Bill, I can now move forward with confidence in refurbishing that power supply board.
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Old 27th Jan 2022, 6:34 pm   #3
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Default Re: Solartron 7065-7055 voltmeter PSU

FWIW, on mine R1 had failed open circuit. 370 odd volts was too much for a standard size carbon 1/2 watt.

dc
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Old 28th Jan 2022, 4:42 am   #4
Ziginox
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Default Re: Solartron 7065-7055 voltmeter PSU

Thanks, I saw your posts working on yours, which led me to asking WME_bill about the rest of the manual! So far the power supply seems operational, it just has a really nasty 20KHz whine that makes it almost painful for me to use. Really beautiful unit otherwise. Mine was built late '77, and was last calibrated in 2010! Got it for a song along with some other goodies, it seems like a really useful and precise unit still. I'd just like to make it more bearable to be around!

Post-repair, does yours make a similar ~20KHz noise? You can see the spike in the screenshot below.
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Old 28th Jan 2022, 3:35 pm   #5
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Default Re: Solartron 7065-7055 voltmeter PSU

No, I can hear nothing, although my hearing is not going to get much that high! I checked with my phone / mic / FFT analyser and nothing shows up. I do see a decent amount of background hash at 20KHz so I assume I would see it if it was there.

dc
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Old 28th Jan 2022, 5:22 pm   #6
Ziginox
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Thumbs up Re: Solartron 7065-7055 voltmeter PSU

Quote:
Originally Posted by dave cox View Post
No, I can hear nothing, although my hearing is not going to get much that high! I checked with my phone / mic / FFT analyser and nothing shows up. I do see a decent amount of background hash at 20KHz so I assume I would see it if it was there.

dc
Thank you so much, I was worried that the 45 year old power supply was just noisy by design. Hopefully replacing the old caps quiets it down, as it really does get painful.
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Old 28th Jan 2022, 6:22 pm   #7
dave cox
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Default Re: Solartron 7065-7055 voltmeter PSU

Maybe worth checking the power consumption to eliminate the possibility that yours is working extra hard ?
I just checked mine, it pulls 27W / 40VA from the wall at 246V rms.
A little more at first power on, no doubt the zener getting up to temperature.

You could try some hot melt glue around the pot-core if all the capacitors are good.

It might be amusing to try to measure the input impedance on the 10V range

dc
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Old 28th Jan 2022, 6:35 pm   #8
Ziginox
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Default Re: Solartron 7065-7055 voltmeter PSU

Quote:
Originally Posted by dave cox View Post
Maybe worth checking the power consumption to eliminate the possibility that yours is working extra hard ?
I just checked mine, it pulls 27W / 40VA from the wall at 246V rms.
A little more at first power on, no doubt the zener getting up to temperature.
That is something I had thought of, but I don't yet have any sort of power meter. I've been waffling in between getting either a kill-a-watt style unit, or getting a clampmeter and line splitter. I'll definitely give it a shot, as excessive impedance on the PSU's output caps putting extra load on the PSU crossed my mind. Shame I don't have a thermal camera to point at them...

I find it surprising that a unit this old has a universal voltage power supply, considering many other bench meters much newer still have the manual switch on them.
Quote:
It might be amusing to try to measure the input impedance on the 10V range
No kidding, >10 gigohm!

Another question for you, does your unit have the RS232 interface? (Option 70555) installed? I've been trying to get data out of it, but can't seem to get a peep. I can see it pull the transmit line low when powered up, but try as I may, I can't get it to transmit any data. It doesn't help that the manual is not clear on setup when the GPIB option is also installed, as my unit has.
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Old 31st Jan 2022, 11:45 am   #9
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Default Re: Solartron 7065-7055 voltmeter PSU

If I recall correctly, I needed to remove the GPIB module before the RS232 module would work. If both are fitted the device only listens on GPIB but can interpret RS232 commands coming over the GPIB bus (why).

As for 'mains' power meters, some of the cheap in-line devices work surprisingly well. A lot of them don't have much resolution at low power, but others are decently accurate even sub 1 watt. I think I paid less than $25! (eqv) but that model is no longer available Look for one that has been tested & recommended

dc
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Old 31st Jan 2022, 4:57 pm   #10
Ziginox
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Thumbs up Re: Solartron 7065-7055 voltmeter PSU

Quote:
Originally Posted by dave cox View Post
If I recall correctly, I needed to remove the GPIB module before the RS232 module would work. If both are fitted the device only listens on GPIB but can interpret RS232 commands coming over the GPIB bus (why).
I had suspicions about this, but the manual leaves a bit to be desired. I'll have to try pulling it and see what happens. Once you'd disconnected the GPIB option, was it "just" as simple as the manual states? I.e., push the sample button and it spits a reading out the RS232 interface?

Quote:
Originally Posted by dave cox View Post
As for 'mains' power meters, some of the cheap in-line devices work surprisingly well. A lot of them don't have much resolution at low power, but others are decently accurate even sub 1 watt.
Yep, that's exactly what I've been having trouble finding; not many get into the sub-1W range. Kill-a-watt had one, but I can't seem to find it anywhere. Perhaps that's even the same model you mentioned.

Anyway, thanks for your input, I'll definitely try pulling the GPIB interface and see what happens!
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Old 1st Feb 2022, 8:01 am   #11
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Default Re: Solartron 7065-7055 voltmeter PSU

Thank you, Dave! I removed the GPIB interface (even had a spare ESD foam box to store it in!) and played with the DIP switches a little bit. I was finally able to get measurements out and remotely control the meter over RS232. Now, just to quiet the thing down and get some replacement feet on it!
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Old 11th Feb 2022, 2:13 am   #12
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Default Re: Solartron 7065-7055 voltmeter PSU

Quote:
Originally Posted by dave cox View Post
Maybe worth checking the power consumption to eliminate the possibility that yours is working extra hard ?
I just checked mine, it pulls 27W / 40VA from the wall at 246V rms.
A little more at first power on, no doubt the zener getting up to temperature.
dc
Finally got my power meter in, and it sits right around 28-29W after it has warmed up for half an hour, after peaking at 32W for a minute or so during power-up. That's at 117v, of course.
The caps are on their way as well, though. I was using the meter the other day and it shut off, only powering up a few minutes later, so I think a recap and a good go-through is in order.

Last edited by Ziginox; 11th Feb 2022 at 2:13 am. Reason: Forgot some info.
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