TRS 80 Power

[abruno17]

I’ve own my TRS 80 Model 4 for two years and I knew what I was getting into. It’s not developed a habit of spontaneous rebooting. I’ll start typing something the text will start to wobble around the screen and shrink and grow before the computer will reboot. Or sometimes when I boot I’ll hold the break key and the computer will just keep rebooting in a cycle before finally turning on and most of the time the text is unstable. I believe this means that there is under voltage but I’m sure if this true any ideas what is causing this and what should I do?

 

[Trash-Eighty]

The first thing I would do is checking the power supply for cold solder joints. Especially on the output voltage connector.
Do not jiggle the output connector (with the cable attached) when the TRS-80 is powered on. When cold solder joints are present this could result in a ground loss which can lead to severe damage to the video board. This happened to me.

 

[ldkraemer]

Trash-Eighty is correct. Carefully raise the top off the Model 4, making sure you watch the neck of the CRT tube through the vents.
Do be careful to not break the end of the CRT. Lay the top on it's left side to the rear of the Computer.

Remove the Tandy Supply and reflow all the Pins on the Supply. If you look closely you will see rings around each Pin as it is loose
from the PCB. It shouldn't take long to re-solder the pins. Then you are good to go. If it's an Astec Supply you shouldn't have
problems, as they seem to be more robust.

You might want to replace the RIFA (Square) Caps while you are working on the Tandy Supply.

Larry