Dead 130XE - fixable?

[KLund1]

I got a dead 130ex.

The PSU I'm using is good, as it working with other 130XE's, & 800XL's, before and after testing this dead 130XE

Symptoms:

No picture at all, no lines, no change in screen whatsoever, curing or after power on (only using monitor jack)

No sound on startup

No keyboard LED lit

No chips are warm just after boot, or 1 minute, or 5

No burnt smell. No melted spot noticeable on front or back. No apparent damage anywhere

All Caps look ok, but I do not think that is a good test.

The large cap just behind and left of the power switch seems to get a bit warming after a long time.

Rotating the color control makes no change on screen.

 

I have a multi-meter but do not know when to touch to see if there is voltage.

I think it is a lost cause for my level of repair. Yes.No?

Thanks

 

 

[48kRAM]

Hmm - no power LED. That sounds like a big clue to me, so, I quickly found some schematics for the 130xe and.... I can't locate the power LED on the schematics. So I can't guess at what could be causing the lack of a power LED (unless the LED is burned out).

 

The diagnosis from here would be to validate the power supply. You can check this at the power pins of any of the chips. Here's the pinout for the RAM chips:

 

http://www.minuszerodegrees.net/memory/4164/4164_list_4.jpg

 

So you want to measure voltage between pins 8 and 16. Follow the diagram and not the chip orientation via the notch. It should read 5 volts.

[+Nezgar]

Power LED in 130XE is sent through the keyboard Mylar... way down the line

[KLund1]

Thanks,

No volts on ram pins. There is 5 volts from the main switch going on to the board. As I said above the PSU is good, working on many other machines.

[adam242]

Is there power coming out of the switch as well as going in? You should have 5 volts on two legs of the switch when its turned on.

[Kyle22]

That large cap that's getting warm may be shorted, and it damages your power supply every time you try it.

Remove the cap and see if the LED comes on.

[KLund1]

Adam242 I tested the legs, and there is 5 volts.

Kyle22 Will it damage it (the mb) any more without the large cap? The large cap only gets a little warmer after a long time, say 5 minuets, but it barely noticeable.

[+DrVenkman]

I really doubt the large cap on the board is failed; when they go, the usually bulge and leak, and then you can see it the split in the cap and/or the electrolyte leaking out.

 

Are any of the chips on your board socketed? If so, remove and reseat them. Sometimes it's just a bit of corrosion over the years and and reseating will correct the issue.

 

Some more quick and easy things to check with your multimeter:

 

1. Pin 8 on the 6502

2. Pin 21 on the ANTIC

3. Pin 3 on the GTIA

4. Pin 17 on the POKEY

5. Pin 20 on the 6520

 

All of these should be showing +5V. If they are, and system is still not booting, chances are either you've got bad RAM or a bad major IC (6502 or ANTIC).

[Kyle22]

If you have 5V on the cap, then it's not shorted and pulling the power supply down. That is good.

I would follow the path the power takes. Maybe an open inductor or poor solder joint is the culprit.

 

Temporarily removing the cap won't hurt, but it's not necessary if its not shorted, swelled or leaking.

[+DavidMil]

Some more quick and easy things to check with your multimeter:

 

1. Pin 8 on the 6502

2. Pin 21 on the ANTIC

3. Pin 3 on the GTIA

4. Pin 17 on the POKEY

5. Pin 20 on the 6520

 

All of these should be showing +5V. If they are, and system is still not booting, chances are either you've got bad RAM or a bad major IC (6502 or ANTIC).

 

Check the three inductors (L1, L2, L3) to make sure that 5volts is going to all three of the 5 Volt rails. Does it look like anyone has done

any after market modifications on the computer?

 

DavidMil

[KLund1]

I got nothing on testing those pins. So I though I'm getting nothing anywhere. what is the lowest common denominator? The switch. I swapped it out with a known good one, and I got some life!

I get a flashing screen of what look like light gray GR9 1 pixel wide vertical bars across the whole screen. there are two parabola on right. These all move up the screen in 1/3 screen increments.

The pins above jump from 0v to 5v with each flash. No ram IC's are getting warm. All IC's are soldered on. no sockets.

Next step in testing? if any?

Thanks again for all the help!

[+DavidMil]

That is a strange problem. My first thought is that it is one of the big chips, but it could be a funky cap or a bad transistor too. With all the chips soldered down,

you going to have a fit trying to get to the bottom of this. I think that what I would do is raise one leg of one of the three inductors L1, or L2, or L3 and look for a

change in the display. If raising one does nothing, leave it up and try raising another. If that does nothing put the first leg down and raise the last inductor. This

will at least give you an idea of which set of chips or components connected to each 5 volt rail are causing the problem. The 6502 chip (CO14806) is not soldered

down is it? Just for an hopeful easy fix you may try swapping that one out first. My fist guess would be the GTIA or Antic chip if replacing the CPU does nothing.

You might want to wait a bit and see if someone has had this symptom before and has a better idea of what the problem could be.

 

One word of caution: When you raise the leg of the inductor that supplies power to the video circuitry of course the screen will go black. The above method is just

a crude first check to isolate a quick fix.

 

David

[shoestring]

Dead machines can hide many faults.

 

Take a picture or short video of the display you're getting now. That might help a little more than just a description.

Edited July 12, 2017 by shoestring

[KLund1]

Thanks all,

This is getting beyond my abilities, and amount of time I can spend on this one.

It will be put up for sale, so a smarter person can see what they can do with it.

Many thank again for all your help.