UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Test Gear and Workshop Equipment

Notices

Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

Closed Thread
 
Thread Tools
Old 3rd Jan 2018, 10:28 pm   #1
1980s_john
Tetrode
 
Join Date: Apr 2005
Location: Ipswich, Suffolk, UK.
Posts: 59
Default Thurlby K2 repair

Hi,

I came across a PL320 power supply with the K2 add-on, worked apart from the main K2 (30V 1A) output which was dead. I took it apart (service manual for K2 is at the back of the PL320 manual I found on line), this was a right PITA to get access to the PCB. I found that there was 0V across the main smoothing capacitor for the 30V output, should be about 55V. I found that the bridge rectifier (made up of 4 x 1N4003 diodes) was fried, with blackening on the PCB. As the output is current limited to 1A, and 1N4003 is only rated at 1A maximum, I guess these parts are a bit under-specified. I found some BYV27-200 diodes (rated 2A / 200V) which seemed a much better idea than the original 1N4003 diodes so fitted these, normal operation was resumed.

I was not over-whelmed by the build quality of this old power supply, there were a couple of cuts on the PCB with resistors and capacitors soldered on the track-side, so maybe this was an early version and later ones have the fixes on a revised PCB. Transformers looked in very good condition so hopefully has many more years of life left.

Regards,
John
1980s_john is offline  
Old 3rd Jan 2018, 11:30 pm   #2
MrBungle
Dekatron
 
MrBungle's Avatar
 
Join Date: Jun 2016
Location: London, UK.
Posts: 3,687
Default Re: Thurlby K2 repair

Congratulations on your repair. When I had a brown cased PL310 I must admit I wasn't too happy with the build quality nor specification of the components. One to watch out for is that the main filter capacitor (at least on mine!) was missing a bleeder resistor so quite happily sat there with around 50v across it when it was turned off and unplugged. Woke me up when I shorted it by accident!

The later PL units (grey ones) are rather better made using modular connectors, neat wiring and very well made boards, much easier to source potentiometers and modern safety features. I own a PL310 and just bought a PL154 yesterday as a comms supply from the later series. Worth swapping out for a later model if you ever see one going cheap!
MrBungle is offline  
Old 4th Jan 2018, 12:09 pm   #3
mhennessy
Dekatron
 
Join Date: Jul 2007
Location: Evesham, Worcestershire, UK.
Posts: 4,241
Default Re: Thurlby K2 repair

Well done

These early models are a pain to work on, but at least they're pretty reliable and faults tend to be relatively straightforward when they occur. As a pre-emptive measure, I'd consider changing the electrolytic capacitors on the control PCBs at this age, as they can leak and cause problems. The wire-wound potentiometers can be responsible for small amounts of voltage drift - nothing that causes problems, but useful to know about. Other than that, I've found them to be excellent, despite the internal build quality.

Just to confuse us all, the internal changes didn't coincide with the change from brown to grey. The internals changed at some point before the case did: https://www.vintage-radio.net/forum/...ad.php?t=50989

The reliable way to tell which version of the innards you have is to look at the damping switch. Later models use a small square push-button, whereas the early ones used the larger rocker switch. Well, on the PL320 side, at least; I know less about the K2 modules. Also, the position of the earth binding post moved from beneath the row of positive/negative output/sense terminals to alongside them. Hopefully useful tips for those buying second-hand

Also, it's worth saying that these days, TTi are very helpful if you need schematics, manuals, etc. That wasn't always the case, so it was nice to discover that they'd changed their approach to support, and as I result, I'd always recommend their products, old or new.
mhennessy is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 4:58 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.