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Fixing a broken VIC-20


bluejay

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A year or so ago, I accidentally must have done something wrong with the video cables of my vic 20; it suddenly powered off, blew a fuse, and then a capacitor. I replaced the fuse and capacitor, but it still won't turn on. I'm not sure if the power supply still works. It's the non-cr 2 pin one, that outputs 9v AC. How do you measure AC with a multimeter?

After reading Ray Carlsen's repair page thingy, I suspect perhaps the KBPC802 bridge rectifier is bad. But the question is, how did shorting something in the video port blow the fuse, blow C58, and the rectifier? Anyways, is there a way to confirm whether something is broken, or something else that might have been fried?

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Your multimeter should have an AC setting.  Most of the AC adapters supplied way more than 9V, especially unloaded.

So you shouldn't be surprised to see 13vAC or more (tho not much more) on the adapter when you test.

 

In fact, my Commodore adapter says it is a 13v adapter.

 

That said, if your multimeter won't measure AC, you could try just measuring for 5v off of the voltage regulator.

Of course, that wouldn't tell you if it was the PSU or the voltage regulator (or something in between) that was the problem.

 

It is weird that it blew more than just the fuse, as that is the standard thing that blows when it happens.

 

Note, you don't have to use AC.

You can use a 9V to 12v DC adapter (just make sure it is 2+ amps).

 

I use a 12vDC adapter to power my 2nd Vic-20.  Works fine.  The main thing that won't work is some devices on the user port that apparently might use AC voltage.  (Not sure what devices those would be?  Modems?)

But basic usage, floppy drives, and tape drives will work fine with DC input.

 

 

Edited by desiv
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1 hour ago, desiv said:

Your multimeter should have an AC setting.  Most of the AC adapters supplied way more than 9V, especially unloaded.

So you shouldn't be surprised to see 13vAC or more (tho not much more) on the adapter when you test.

 

In fact, my Commodore adapter says it is a 13v adapter.

 

That said, if your multimeter won't measure AC, you could try just measuring for 5v off of the voltage regulator.

Of course, that wouldn't tell you if it was the PSU or the voltage regulator (or something in between) that was the problem.

 

It is weird that it blew more than just the fuse, as that is the standard thing that blows when it happens.

 

Note, you don't have to use AC.

You can use a 9V to 12v DC adapter (just make sure it is 2+ amps).

 

I use a 12vDC adapter to power my 2nd Vic-20.  Works fine.  The main thing that won't work is some devices on the user port that apparently might use AC voltage.  (Not sure what devices those would be?  Modems?)

But basic usage, floppy drives, and tape drives will work fine with DC input.

Okay, thanks!

For now I'll just order a replacement rectifier since they only cost like $5. I can't order one now but I'll have one by 2021. Meanwhile I'll continue to tinker with my multimeter. The thing is, it does have an AC setting, but I can't figure out how it works. Actually, I have no understanding of how AC works in general, to be brutally honest. I tried sticking both of the probes into each of the holes in the power connector, one in one of the jacks and one on ground, but it was always zero. Am I doing something wrong or is the power supply dead?

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25 minutes ago, bluejay said:

I tried sticking both of the probes into each of the holes in the power connector, one in one of the jacks and one on ground, but it was always zero. Am I doing something wrong or is the power supply dead?

Don't try to find ground for testing AC.

 

It can depend on your multimeter.

My analog multimeter has 3 AC settings.  50v, 250v, and 500v.

So for testing the output of the power supply, I'd set it for 50v and place the leads in each of the two holes.

The meter should go up about 20%. (about 10v)

 

My digital meter also has several AC settings, 200m, 2, 20, 200, 750.

So for measuring the output of the Vic-20 AC adapter, I'd select 20 and hope that it goes about halfway (about 10v)...

 

You don't have to worry about which lead is plugged into which hole in the Vic 20 PSU.  The current alternates in both lines.

 

There are a lot of different meters out there.

 

The easy way to test the multimeter with AC is to test a power strip on the 250v setting.  If you are in the US, it should go halfway.

****That said, be careful as that is full mains voltage.  So don't do that unless you feel comfortable doing that...****

 

But, if the multimeter is working for AC in general, but not for your Vic PSU, then that is probably what died...

 

Edited by desiv
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9 minutes ago, desiv said:

Don't try to find ground for testing AC.

 

It can depend on your multimeter.

My analog multimeter has 3 AC settings.  50v, 250v, and 500v.

So for testing the output of the power supply, I'd set it for 50v and place the leads in each of the two holes.

The meter should go up about 20%. (about 10v)

 

My digital meter also has several AC settings, 200m, 2, 20, 200, 750.

So for measuring the output of the Vic-20 AC adapter, I'd select 20 and hope that it goes about halfway (about 10v)...

 

You don't have to worry about which lead is plugged into which hole in the Vic 20 PSU.  The current alternates in both lines.

 

There are a lot of different meters out there.

 

The easy way to test the multimeter with AC is to test a power strip on the 250v setting.  If you are in the US, it should go halfway.

****That said, be careful as that is full mains voltage.  So don't do that unless you feel comfortable doing that...****

 

But, if the multimeter is working for AC in general, but not for your Vic PSU, then that is probably what died...

 

Well, my cheap multimeter just has one AC symbol on the rotating switch thing.

The probes measures 120V AC from the wall, but it's zero when it's in the power supply holes. I guess the supply died. You mentioned I could use 12vdc?

I noticed the C128 power supply outputs 9vac, but it says 1.0A NOM. I'm guessing that wouldn't work?

Edited by bluejay
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Just now, bluejay said:

Well, my cheap multimeter just has one AC symbol on the rotating switch thing.

The probes measures 120V AC from the wall, but it's zero when it's in the power supply holes. I guess the supply died. You mentioned I could use 12vdc?

It's trickier with only a 120v setting, since that would only be a 10% or less amount of motion on an analog meter, but you should still be able to see it move with that.

 

Yeah, you can get an AC Vic to work with 9-12 volts DC.

The first thing the Vic does internally is convert the AC to DC.  And DC will just convert to DC.

 

But the Vic does want 3amps or so.  So it's a beefier PSU than some out there..

(I said 2amps above, but I meant 3amps.  That was what Ray recommended.)

 

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1 minute ago, desiv said:

It's trickier with only a 120v setting, since that would only be a 10% or less amount of motion on an analog meter, but you should still be able to see it move with that.

 

Yeah, you can get an AC Vic to work with 9-12 volts DC.

The first thing the Vic does internally is convert the AC to DC.  And DC will just convert to DC.

 

But the Vic does want 3amps or so.  So it's a beefier PSU than some out there..

(I said 2amps above, but I meant 3amps.  That was what Ray recommended.)

 

It's a digital multimeter.

I'm depressed now. All my power supplies that output 9 volts is like 850mA, and those that output anywhere near 3 amps is like 18 volts. The closest I have is a 5200 power supply, which is 9V, 2A.

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3 minutes ago, bluejay said:

The closest I have is a 5200 power supply, which is 9V, 2A.

Getting into theoretical for me here, so take this as a grain of salt.

Ray was saying that the bridge rectifier drops the voltage about 2v.  So 9v would drop to 7v, but that should probably still be fine as it then regulates it down to 5v.

 

And 2A is probably fine, especially if you are just testing and don't hook up any peripherals.

 

For a quick test, to see if your Vic still works, I think 9vDC at 2A should be fine.

But I personally wouldn't run it on that long term, and 3A or so adapters are pretty cheap.

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20 minutes ago, desiv said:

Getting into theoretical for me here, so take this as a grain of salt.

Ray was saying that the bridge rectifier drops the voltage about 2v.  So 9v would drop to 7v, but that should probably still be fine as it then regulates it down to 5v.

 

And 2A is probably fine, especially if you are just testing and don't hook up any peripherals.

 

For a quick test, to see if your Vic still works, I think 9vDC at 2A should be fine.

But I personally wouldn't run it on that long term, and 3A or so adapters are pretty cheap.

Can I wire the supply to any of the pins or is there a specific direction I should wire it to?

I couldn't wait; so I tried it, and it seems to work!

Edited by bluejay
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5 minutes ago, bluejay said:

Can I wire the supply to any of the pins or is there a specific direction I should wire it to?

On the Vic side, either of the 2 pins.

On the source side, just make sure you get a gnd and 9v (at 2A).

(Not familiar with the 5200 PSU.  If it is only those 2 wires, then it doesn't matter which ones.  The rectifier in the Vic will handle all that.)

 

Also, I am assuming you tested/replaced the fuse on the Vic if needed?

Edited by desiv
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8 minutes ago, desiv said:

On the Vic side, either of the 2 pins.

On the source side, just make sure you get a gnd and 9v (at 2A).

(Not familiar with the 5200 PSU.  If it is only those 2 wires, then it doesn't matter which ones.  The rectifier in the Vic will handle all that.)

 

Also, I am assuming you tested/replaced the fuse on the Vic if needed?

Yep, I plugged in the psu plug to one of the pins, and folded up a paper clip and stuck it between the outer part of the jack and the other pin. I replaced the blown fuse and capacitor a while ago, and now it works perfectly! Thanks a lot :) 

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1 minute ago, bluejay said:

Yep, I plugged in the psu plug to one of the pins, and folded up a paper clip and stuck it between the outer part of the jack and the other pin. I replaced the blown fuse and capacitor a while ago, and now it works perfectly! Thanks a lot :) 

Glad you know it works!!!

 

I went with a 12v 3A PSU from Ebay and soldered on a cord I had that fit the Vic.

 

There are people that say it would be better to go with a 9V 3A, because it will produce less heat when it rectifies / regulates down.

 

I went with the 12v, as my original PSU was around that voltage.

 

YMMV.  ;-)

 

Enjoy!

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2 minutes ago, desiv said:

Glad you know it works!!!

 

I went with a 12v 3A PSU from Ebay and soldered on a cord I had that fit the Vic.

 

There are people that say it would be better to go with a 9V 3A, because it will produce less heat when it rectifies / regulates down.

 

I went with the 12v, as my original PSU was around that voltage.

 

YMMV.  ;-)

 

Enjoy!

I loaded up a few games from cartridge, tape, and even disk, and they all worked really well. I'm really glad I finally have a working VIC-20 again :) 

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