Systron Donner TL8-3 Trygon Power Supply repair - diyAudio
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Old 27th March 2015, 03:04 AM   #1
diyAudio Member
Join Date: Feb 2013
Default Systron Donner TL8-3 Trygon Power Supply repair

Hi Gang! Sooo,
I picked up this beautiful old Systron Donner Triple output power supply for a song and when I received it, I discovered the +32VDC supply was dead.
Researched via the internet, only to discover that Systron Donner was ignominiously acquisitioned, without any regard to its quality & provenance, and as a result there isn't much documentation out there.
Nevertheless, I managed to find a copy of the owners/service manual and was able to discern (after MUCH ado) that the problem was with the "Voltage amplifier circuit" The other outputs (+8 VDC & -)
32 VDC were fine.
The schematic I obtained was for a German division of Syst, Donn. & reads many different input voltage configurations (evidently available via various adapters or mods.) My specific unit seems to be made in America and has no input voltage configuration options. There is a trouble shooting chart in this manual, and I determined that there was a shorted diode (undocumented on the schematic) that was the culprit.
My one concern was that the troubleshooting chart specified a 26VDC spec across the +32VDC supply cap & I read 49VDC...
Since the -32VDC supply was fine(same -49VDC reading on it's supply cap.), & there was a questionable manuals(European?) from a center tapped trans., (& that was the only source I could see that would increase the voltage spec that much), I decided to attempt the repair. Specifically, I replaced the failed diode(TR4148) in that Voltage amplifier circuit, which, after I replaced it,(4148) caused the supply to operate normally.
All was well in the world, and I calibrated the outputs to my DMM and buttoned it up....
Well, as you could guess, 5 minutes later as I played with the thing, IT FAILED AGAIN....
I assumed it was the diode I had replaced since there was a question about the spec. on the diode.(Evidently the original was Mil. Spec 4148)
However, after I removed it, the new diode was intact.
What I found, was that the associated transistor (2N3638A)(Q6), had shorted, along with another diode (CR8) & another transistor (2N3638A) in the same circuit(Q5)!
WOW, pretty steep price to pay!
So, I'm back to the drawing board.
I have a couple of 2N3638 PNP transistors I could put in, but my concern is the high voltage reading of those caps & whatever difference there would be between the 2N3638 & 2N3638A transistors (according to the troubleshooting routine...)
The transformer is Center tapped & there are no specs listed.
It measures 74VAC from the outer poles and 37.5VAC from center tapped outputs.
Is there some way the center-tapped feed is not working, and as a result, the full output of the secondary is feeding the circuit? I'll post the schematic, and throw the problem out there for ideas.

If anyone has a suggestion, I'd welcome it!

Hmmm, Issues uploading the schematic....
I'll have to post the link where I got it instead. This is for the whole manual, from which I couldn't extract the single page from...

Last edited by EndlessSummer; 27th March 2015 at 12:50 PM. Reason: Added link to schematic, corrected a reference I made to the Neg 32VDC supply cap value.
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Old 7th July 2015, 03:25 AM   #2
bachch is offline bachch  United States
diyAudio Member
Join Date: Jan 2007
Did you ever get this working? My TL8-3 has 40V at the collector of Q101 (+32V supply cap) with no load. Looking at the schematic over-voltage seems the most likely Q5,Q6 death mode (if resistors aren't shorted).
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