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Old 19th Nov 2018, 6:14 pm   #1
dgs2001
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Join Date: Nov 2018
Location: Gloucestershire, UK.
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Default Hello and PL320QMD pointers please

Hi All,

Newby so please go easy

I have acquired an old PL320QMD which seems to function well. Its in a grey case whioch I believe makes it a later model.

All outputs are working to expected voltage and current.

I do have one problem with it though, the voltage display on the master side is not reading. It stays hovering between 0 and 0.01 volt although the actual output seems solid and responds to coarse and fine control as expected.

I do have a downloaded service manual, but am still learning so would appreciate some pointers.

Thanks
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Old 20th Nov 2018, 1:18 pm   #2
See_Mos
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Location: Ossett, West Yorkshire, UK.
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Default Re: Hello and PL320QMD pointers please

If I am reading the circuit correctly!

With the output turned off does the voltage display show the preset voltage?

From your description I assume the display is not showing the output voltage. If you are lucky it might be just a problem with preset resistor VR6. Turn up the voltage and turn the output on then measure the voltage from -VS terminal to VR6 wiper. If it is close to zero turn the power off and measure the resistance from +V out to +S and -V out to -S, both should measure 2K2 also the voltage between +S and -S should be the same as the output voltage.

If you are tempted to twiddle VR6 to see if it is noisy then be sure to mark the setting first.

The next suspect would probably be the multiplexer IC 3 type CD4052

Last edited by See_Mos; 20th Nov 2018 at 1:24 pm.
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