Thurlby Thandar RSComponents Bench Power Supply

johnwass

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Sep 26, 2008, 5:56:36 PM9/26/08

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I have an old 30V 2A bench power supply badged RS Components Code 610-461
which was made by Thurlby, now Thurlby Thandar Instruments (tti). The
current meter shows OFL which I found out means overload. It has linear
regulation using a couple of 3055s and looks similar to the EL series on the
tti UK website http://www.tti.co.uk/products-tti/psu/psu-bench.htm
Internally it is very similar to an RS Components 610-477 although that is a
dual 30V 1A power supply. I have given it a quick check and can't see
anything obviously wrong. Does anyone have a schematic or any other info
that might help me repair it?

Thanks

John

Adrian C

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Sep 26, 2008, 6:56:43 PM9/26/08

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johnwass wrote:
> I have an old 30V 2A bench power supply badged RS Components Code 610-461
> which was made by Thurlby, now Thurlby Thandar Instruments (tti). The
> current meter shows OFL which I found out means overload.

On my Thurlby's (considerably older though), OFL means you have the
current limit control set fully clockwise equating to the 'no current
limit' setting (let me smoke & catch fire first....). This when the
power out switch is off.

Try turning the control down? Could be the control itself is faulty if
no change.

--
Adrian C

johnwass

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Sep 26, 2008, 8:32:16 PM9/26/08

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Adrian

Thanks. However, current limit control setting makes no difference. Always
shows OFL. Thought it was unlikely to be the control but I will try swapping
it for a different one to see if it makes any difference.

John

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Ron(UK)

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Sep 27, 2008, 7:11:06 AM9/27/08

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That happened to mine (Thandar TS3021S) There was a diode soldered
directly across the output terminals which was shorted - I suspect
someone had use it to charge a gelcell and connected it up the wrong
polarity.

Ron(UK)

johnwass

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Oct 3, 2008, 9:53:56 AM10/3/08

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Current pot resistance checks out. All 3 diodes connected between outputs
are fine.

John
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Adrian C

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Oct 3, 2008, 12:16:06 PM10/3/08

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johnwass wrote:
> Current pot resistance checks out. All 3 diodes connected between outputs
> are fine.
>
> John

OK. If your assertion that the OFL display means overload is correct,
I'd take that to mean that its an indication from the display modules
built-in ADC that there is excess voltage at it's input compared with
it's specifications for full scale 'deflection'.

Can you see what part they used, find a datasheet and trace the input
pin(s). Then stick a meter there, attach a load and see if on varying
the output voltage if there is anything sensible changing for these inputs.

I'm guessing all of the circuitry still is plain discrete analogue
driven (compared with my old PL154) and you might find the culprit
through simple fault finding. If it is a silicon jungle chip maybe not.
Though a manual has to be found from somewhere ...

--
Adrian C

Franc Zabkar

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Oct 3, 2008, 6:30:21 PM10/3/08

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On Fri, 26 Sep 2008 22:56:36 +0100, "johnwass"
<crops...@hotmail.co.uk> put finger to keyboard and composed:

If your PSU senses the current via a low ohms series resistor, then an
open resistor may produce the observed symptom. In any case it may be
a good place to start troubleshooting.

- Franc Zabkar
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Please remove one 'i' from my address when replying by email.