• Please review our updated Terms and Rules here

TRS-80 Model 4 won't power up. :(

A

ardsleytank

Experienced Member
Joined
Nov 15, 2015
Messages
282
Location
Tennessee
Hi all! Been a while, I know.


So... I think I may have made a topic about this before, but I thought I had fixed it. As apparently I hadn't.

Any way, my Model 4 won't power on. When I flip the switch, the power supply just gives a faint ticking sound as well as the drive lights flickering in time with the tick.

Mine has the one 65W(? I think?) Power supply, and I have not changed out the original filter caps for new ones yet.

Any advice would be appreciated.
Many thanks, and Merry Christmas!

Peter
 
Is it the Tandy supply? There was a service bulletin on the potentiometer that adjusts the 5v rail being weak/crudded up. I have solved it by adjusting that potentiometer and watching the 5v rail to ensure its at spec. If they fixed it, there will just be two resistors where it was.

I also had a bridge rectifier go out once that caused it.

mean well supplies are on sale at jameco and I've used them as well. Pretty sure Ian has some on ebay for sale too.
 
Also check the power supply connectors on the back side of the power supply itself. I had a couple where the power connector solder joints were barely making contacts. doing what you described. So I reheated the contacts and that got them working fine. Just an idea to try. if needed I do have a couple extra supplies available. See PM.
 
Yes, it is the Tandy Power supply. I checked and I couldn't locate the potentiometer described.

Also, Chromedome45, I have in the past reflowed the solder joints as you described, unfortunately with no results. I sent you a PM. :)

Thanks again, I look forward to your replies.
Peter
 
Before you start adjusting the Pot, have you wired a 60 Watt Incandescent Light Bulb in
series with the Line (HOT) lead and see if it shines bright when the Power Supply is
connected to a load like an old Floppy or Hard Drive? One that you can afford to use
as a dummy load? Or you need some type load that will allow the power supply to
regulate.

DO NOT just start by adjusting the POT. That will just cause more problems.

Give us the results of this test. Then we will test the Bridge with your meter as
step 2.

Larry
 
You must log in or register to reply here.
Back
Top