VIC-20 2-pin Power Supply question

[Britishcar]

I have a VIC-20 that I've had for many years that has begun to exhibit a habit of booting to a black screen, and then after turning it off and back on again, booting normally. So the issue is intermittent, etc.

 

It occurred to me to check the power supply. It is a 2-pin early supply and the VIC is also a very early machine with the large motherboard and giant heat dissipation stuff inside, etc.

 

The power supply is a 2-pin #902502-01 labeled output 9V AC 3A.

 

Here's my question: when I measure the voltage at the holes of the pins on the power supply, I get a steady 11.75V AC.

 

So...this sounds abnormal but is it? I know that a system can eat up excess amps as needed but is it normal for the power supply to put out more than 9V to a multi-meter but be the correct amount for the machine, i.e. sort of an "unloaded" output?

 

Attached is a picture of an identical supply.

 

If anyone has a similar PS, what output are you getting? is 11.75V about to fry the machine or is this a healthy normal output?

 

Thank you!

[carlsson]

Yes, I believe the transformer without load will output a higher voltage. Some of those two-prong power supplies are even marked 10V AC. If your VIC-20 takes long to power on, I think there is a capacitor or something that needs to be charged and it could require replacing. I don't remember the exact details but I've read about it many years ago.

[Britishcar]

Thanks, carlsson! I know that a lot of VIC-20's and C64's have gone to that great bit bucket in the sky based on failing power supplies that began to put out too much voltage -- that's what worried me -- that the PS was giving way somehow.

 

The capacitor sounds like a very reasonable idea. I should probably just recap the entire machine...

[zylon]

I'd 2nd that and also replace the voltage regulator inside the console. I'd say you have a capacitor not charging up as fast as it used to for startup. I had a C64C do the same thing few years ago.

The earlier 2-pin power supply setup was the better of the two styles IMHO.

Edited August 7, 2018 by zylon