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From: MarkB on 26 Nov 2009 17:29
Hi

I have a TTi (Thurlby Thandar) TS3021S Bench Power Supply which works fine
but has a slight calibration issue with its voltage display.

According to the specifications, the voltage display should be accurate to
0.2%. Mine always reads low by aboiut 1.5%.

I suspect I can fix this by a simple adjustment of an internal trimmer
resistor. But which one? There are approx. 10 on the main circuit board.

Does anybody have a service manual, circuit diagram, or any other
information that would help me fix this problem?

Thanks in advance for your help.

Mark


From: N_Cook on 27 Nov 2009 03:19
MarkB <markb(a)conceptfp.+.com> wrote in message
news:dpednSEJNPr8nJLWnZ2dnUVZ7omdnZ2d(a)brightview.co.uk...
> Hi
>
> I have a TTi (Thurlby Thandar) TS3021S Bench Power Supply which works fine
> but has a slight calibration issue with its voltage display.
>
> According to the specifications, the voltage display should be accurate to
> 0.2%. Mine always reads low by aboiut 1.5%.
>
> I suspect I can fix this by a simple adjustment of an internal trimmer
> resistor. But which one? There are approx. 10 on the main circuit board.
>
> Does anybody have a service manual, circuit diagram, or any other
> information that would help me fix this problem?
>
> Thanks in advance for your help.
>
> Mark
>
>

Mark each trimmer and also measure whatever the in circuit resistance of
each trimmer is, before speculative adjusting. Perhaps create a WWW repair
brief for others while at it


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/



From: N_Cook on 27 Nov 2009 03:38
N_Cook <diverse(a)tcp.co.uk> wrote in message
news:heo24t$qnc$1(a)news.eternal-september.org...
> MarkB <markb(a)conceptfp.+.com> wrote in message
> news:dpednSEJNPr8nJLWnZ2dnUVZ7omdnZ2d(a)brightview.co.uk...
> > Hi
> >
> > I have a TTi (Thurlby Thandar) TS3021S Bench Power Supply which works
fine
> > but has a slight calibration issue with its voltage display.
> >
> > According to the specifications, the voltage display should be accurate
to
> > 0.2%. Mine always reads low by aboiut 1.5%.
> >
> > I suspect I can fix this by a simple adjustment of an internal trimmer
> > resistor. But which one? There are approx. 10 on the main circuit
board.
> >
> > Does anybody have a service manual, circuit diagram, or any other
> > information that would help me fix this problem?
> >
> > Thanks in advance for your help.
> >
> > Mark
> >
> >
>
> Mark each trimmer and also measure whatever the in circuit resistance of
> each trimmer is, before speculative adjusting. Perhaps create a WWW
repair
> brief for others while at it
>
>
> --
> Diverse Devices, Southampton, England
> electronic hints and repair briefs , schematics/manuals list on
> http://home.graffiti.net/diverse:graffiti.net/
>
>
>

JIC check the "trimmer" ( in circuit) resistance with probes either way
round and note if different

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


From: MarkB on 27 Nov 2009 09:10
I am still hoping someone might be able to tell me which trimmer has the
effect I desire. Experimenting with the trimmers is the final option and if
it comes to that, I might not bother since the unit basically works as is.

But thanks for your advice. The point about measuring the resistance both
ways is a good one - I might not have thought of that.

"N_Cook" <diverse(a)tcp.co.uk> wrote in message
news:heo392$4aj$1(a)news.eternal-september.org...
> N_Cook <diverse(a)tcp.co.uk> wrote in message
> news:heo24t$qnc$1(a)news.eternal-september.org...
>> MarkB <markb(a)conceptfp.+.com> wrote in message
>> news:dpednSEJNPr8nJLWnZ2dnUVZ7omdnZ2d(a)brightview.co.uk...
>> > Hi
>> >
>> > I have a TTi (Thurlby Thandar) TS3021S Bench Power Supply which works
> fine
>> > but has a slight calibration issue with its voltage display.
>> >
>> > According to the specifications, the voltage display should be accurate
> to
>> > 0.2%. Mine always reads low by aboiut 1.5%.
>> >
>> > I suspect I can fix this by a simple adjustment of an internal trimmer
>> > resistor. But which one? There are approx. 10 on the main circuit
> board.
>> >
>> > Does anybody have a service manual, circuit diagram, or any other
>> > information that would help me fix this problem?
>> >
>> > Thanks in advance for your help.
>> >
>> > Mark
>> >
>> >
>>
>> Mark each trimmer and also measure whatever the in circuit resistance of
>> each trimmer is, before speculative adjusting. Perhaps create a WWW
> repair
>> brief for others while at it
>>
>>
>> --
>> Diverse Devices, Southampton, England
>> electronic hints and repair briefs , schematics/manuals list on
>> http://home.graffiti.net/diverse:graffiti.net/
>>
>>
>>
>
> JIC check the "trimmer" ( in circuit) resistance with probes either way
> round and note if different
>
> --
> Diverse Devices, Southampton, England
> electronic hints and repair briefs , schematics/manuals list on
> http://home.graffiti.net/diverse:graffiti.net/
>
>


From: Geo on 27 Nov 2009 09:55
On Thu, 26 Nov 2009 22:29:53 -0000, "MarkB" <markb(a)conceptfp.+.com> wrote:

>Hi
>
>I have a TTi (Thurlby Thandar) TS3021S Bench Power Supply which works fine
>but has a slight calibration issue with its voltage display.
>
>According to the specifications, the voltage display should be accurate to
>0.2%. Mine always reads low by aboiut 1.5%.
>
>I suspect I can fix this by a simple adjustment of an internal trimmer
>resistor. But which one? There are approx. 10 on the main circuit board.

Is the meter a complete panel meter (separate item) with only a few connections
or is it just a display with the A-D on the main PCB?
If it is a panel meter then you could look up the model and/or check the voltage
at its input connections.
If it is just a display then see what chip is driving it and look up the pinout
of that to see where the analogue inputs are


--
Geo
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