View Single Post
Old 18th Mar 2021, 2:51 am   #57
GeraldSommariva
Pentode
 
GeraldSommariva's Avatar
 
Join Date: Mar 2021
Location: Liphook, Hampshire, UK
Posts: 125
Default Re: The Transam Triton Personal Computer

Quote:
Originally Posted by ortek_service View Post

These IC's are normally on the secondary-side of the main 'chopper' transformer. So if that isn't running, then all output side will be dead.
They will be part of the feedback circuit to control the output voltage, and usually drive an optocoupler to reduce the drive to the transformer when the output voltage start to go above what it should be.
The TL494 is a PWM-Controller IC, often used in these.
Thanks for the notes

I got it sort of working a 10uf 50v electrolytic capacitor on the 18v supply rail to the chopper and control circuit. when I checked the 7818 reg on the heat sink there was no output but +35V on the input pin which comes from the secondary winding on the black transformer.

Could not find any optocoupler on the pcb I think the mains isolation is provided by having the chopper drive transistors driven by transformers (T3 T4) it is an old supply from approx. 1982.

The supply should produce +5 +12v and -12v now the +5v is good and works under load the -12v is good but the +12 is +16v. both the 7812 and 7912 regs are being feed with +18v and -18v respectively.

For testing I have been powering the supply from a 300W 12V inverter purchased from Maplin and a 12V SLA battery to give we isolation from the mains so I can use my scope etc.... now need a new 7812 to try!
Attached Thumbnails
Click image for larger version

Name:	20210318_005748.jpg
Views:	60
Size:	139.1 KB
ID:	229454  
GeraldSommariva is offline