Author Topic: Old Thurlby PL320 TGP (Sinclair) Dual channel lab power supply  (Read 2198 times)

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Offline Pete2

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Re: Old Thurlby PL320 TGP (Sinclair) Dual channel lab power supply
« Reply #25 on: March 31, 2018, 02:42:50 am »
OK I have finished replacing all the caps (el and polyester) and trimmers (TME supplied me with 2 pcs of 200k pots and one 1k when I ordered 3 pcs 1k :(, no wonder the cal was so touchy!) + changed the awful sockets for the voltage meter ics to precision ones. The PL320 side is working just fine, have to get a more accurate meter to calibrate it properly.

The other side (K2) which supplies 4-6 V @ 7 A and 0-30 V @ 1 A is not so good. It doesn't have a voltage display, only current and without load it displays 0.14 A. I can load it and it displays the current but doesn't supply over 2 A or so. The voltage is bang on though. Calibration doesn't help, max. current is the 2 A or so.

So looks like it's a repair after all 8) Luckily I got the other ics from TME while I got the caps. Not much there, an LM324 and an LM358. And tons of discrete BJTs. Sadly the K2 schematic is the worse one so could pretty hit and miss to repair.
 

Offline Pete2

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Re: Old Thurlby PL320 TGP (Sinclair) Dual channel lab power supply
« Reply #26 on: April 01, 2018, 02:16:24 am »
Figured out the meter issue, was a broken track due to me replacing the metering ic socket. But the current issue (pun) still remains, outputs only 3.45 A when should get 7+ A. The adjustment just doesn't go far enough. Checked the output stage transistors, they're fine (2 x 2N3055) and the one driving them looks like OK but I don't have a replacement at the moment. Replacing the opamp did not help either.

It's a rather complex circuit with several different ground points and voltages.
 

Offline bd139

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Re: Old Thurlby PL320 TGP (Sinclair) Dual channel lab power supply
« Reply #27 on: April 01, 2018, 02:18:30 am »
Being old thurlby, check for dry joints  8)
 

Offline Pete2

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Re: Old Thurlby PL320 TGP (Sinclair) Dual channel lab power supply
« Reply #28 on: April 02, 2018, 07:23:07 pm »
Well, I think it's working now - and has been the whole time. The 4-6 V side is actually smarter with its current limiting as it's not supplying the entire 7 A when the output is shorted. I had a doubt about this but didn't try it until now.

The calibration instructions say "load the unit to 7 A" and that means not short the output. Not sure what the limit is for short detection but after I constructed a suitable resistor I was able to load it to just over 7 A and set the current limit to 7.35 A as per the instructions. If it detects a short the output current is limited to about 2.65 A.

Now I can finish upgrading some of the wiring (seems a bit thin for 7 A). I already replaced the mains wiring and added a protective earth point. Also I want to add a discharge resistor for the K2 module 30 V / 1 A output. When the unit is switched off, the main cap doesn't discharge at all and that holds 55 V. Not that it's dangerous but when servicing it's nice it discharges eventually.
 


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