GTI+ PSU Repair

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PaulB59
Posts: 3
Joined: 27 Nov 2016 17:19

GTI+ PSU Repair

Post by PaulB59 » 27 Nov 2016 17:28

Hi,

I've have a PT Export I've had from new, it replaced a PT 1 I bought at university and has been used for the last 20-odd years on and off.

I had part of the suspension break on Friday, but managed to fix that by gluing the plastic bits together and refitting. After I reassembled everything the motor ran for a few seconds, then stopped and then started oscillating. I suspect I have a dead GTI+ PSU as it is scorched around the oscillator circuits and me removing it to fix the suspension must have been the last straw for whichever component has gone west. It is a Rev 1.20 and looks in good condition apart from the scorching I mentioned.

Is it worth fixing this, or is a better solution to buy a Heed Orbit and do away with the GTi completely (assuming I can do this)? Alternately, can someone recommend where to get the PSU fixed? There is no major board damage, so I assume it is one of the caps or resistors that have failed. I could even try it myself as I have built electronics before, but I don't have the exact components needed so I'd probably end up replacing everything on the board before I found the fault!

Thanks for any advice you can give!

Paul

willb
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Joined: 10 Jun 2004 17:32
Location: Devon, UK

Re: GTI+ PSU Repair

Post by willb » 28 Nov 2016 00:00

HI,

If you can, keep the GTI board going as it's a split-phase supply (2 ampifiers) which doesn't use a film capacitor across the motor to 'phase-shift' the voltage. A Heed supply will probably use a standard 0.22uf cap and your PT motor will very likely use a motor which uses a 0.39uf - result: it'll not be running properly unless you change it! :(

A friend has a Gti psu on his LPT, (which I managed to fix a couple of years ago) and it's pretty good - a picture would help identify which version you have. Either way, I could probably sort it out for you, with the one caveat: older psu's used a now defunct frequency divider chip - and you say there is scorching around the oscillator area, but they usually heat up around the power resistors at the psu end (high voltage-drop so more heat).

I've used an Export psu (lucky find on the bay), for 10 years or so on a Systemdek with the same motor as you've probably got, so I know the boards really well. They're very similar, but the Gti is the best one IMHO - on a par with Linn's Valhalla (single-phase but a beast power-wise :lol: ).

Post a couple of pix and we'll take it from there.

ATB

Chris.

PaulB59
Posts: 3
Joined: 27 Nov 2016 17:19

Re: GTI+ PSU Repair

Post by PaulB59 » 28 Nov 2016 08:03

Hi,

Here are some pictures of the board. If you need to me take a picture of a specific area, let me know.

I did notice that one of the resistors wobbles in place, although the PCB track still seems intact. I guess it could be a broken track as well?

Best regards

Paul

https://s22.postimg.org/3n5n0cuwd/IMG_6207.jpg

https://s22.postimg.org/bh68lr2p9/IMG_6208.jpg

https://s22.postimg.org/7yu8pd1t9/IMG_6209.jpg

willb
senior member
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Posts: 344
Joined: 10 Jun 2004 17:32
Location: Devon, UK

Re: GTI+ PSU Repair

Post by willb » 29 Nov 2016 01:38

HI Paul,

Unfortunately the pics don't really tell me what I need to know!
An overall view of the board showing the components at either end i.e the IC's near the switch end and the high voltage caps/resistors at the mains end would be much more useful.

It looks different to my friend's version (but that one is late 90's). Wobbly components normally mean a loose solder pad - nothing that can't be sorted. Some new HV stuff is generally a good start (Maplin sell decent caps & 2 watt resistors), better rectifier diodes and maybe the 1uf caps in the amplifiers. The generator end should be ok, as it runs at 15v dc, bar maybe a zener diode or 2, so it shouldn't be too difficult to get it back to spec.

Most of this I either have, or can get in a day or 2 :D

ATB

Chris.

PaulB59
Posts: 3
Joined: 27 Nov 2016 17:19

Re: GTI+ PSU Repair

Post by PaulB59 » 29 Nov 2016 10:23

Hi Chris,

Thanks for the offer of help, it's much appreciated. Unfortunately I am in France for a couple of days, so can't take any more photos until Thursday night. I have two more I took and have inserted them below.

Could you PM an idea of what it might cost to fix? I guess you can only quote worst case without having the board in your hands, but it would be good to have some ballpark number so I know whether it is worth it or perhaps whether I should change the motor and board to a DC version.

Thanks again!

Best regards,

Paul

https://s14.postimg.org/3si4nxz4d/image1.jpg

https://s14.postimg.org/7de0763nx/image2.jpg

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