Macintosh Plus horizontal elongated display

[Retro collector]

Hi guys! My English isn't very good, so please excuse me if i make any grammatical errors or typos. I need some help. I got a Mac Plus, and its electrolytic capacitors were changed on the analog board, the connection ports were resoldered/had new soldering. There were no problems with the soldering. So the problem is that when the mac heats up, the displayed pictures and other sorts of things stretch out of the screen. After i turn it off, and give it some time to cool down, the resolution turns back to normal, but as it gradually starts heating up, it goes right back to stretching out again. I couldn't find any solutions on The Dead mac Scrolls, so any help is appreciated. I put some tape on the screen to indicate displayed image's edge should be

 

[MacTech68]

Are you certain that C1 (3.9uf) cap at the top edge of the analog board was replaced ?

Pics of the analog board would be really helpful.

 

[Retro collector]

Yes the 3,9uf capacitor has also been replaced with a non-polarized foil capacitor. This is not the first time i've done this so i'm done with the basics. I also replaced the BU406 transistor but the there was no problem with itt. The analog board is an International. Its nothing extra

 

[MacTech68]

May I suggest a can of freezer spray on some of the diodes associated with the horizontal circuit.

If you have a look at the pdf below, page 16 details the horizontal circuit.

http://www.maccaps.com/MacCaps/DIY_Information_files/Classic%20Mac%20Repair%20Notes%20.pdf

 

[Retro collector]

I checked the line in the image because it is responsible for the horizontal image, but found no error.

 

[Retro collector]

This Analog board

 

[MacTech68]

Please monitor the +12v and +5v rail as the unit warms up from COLD. What ranges are you getting?

Also, I see some of the capacitors are only rated 85 Degrees C. Lower rated components may often have larger value drift over certain usage conditions - one of which is temperature.

Also, I suspect the 3.9uf cap may be an audio cross-over type. What is it's part number ?

Again, freezer spray might help to locate the cause (though it CAN sometimes lead you up the wrong path).

 

[Retro collector]

Today i changed out all the capacitors, that were labeled for 85°C to 105°C ones. My problem still stands however. After heating up, +12V lines rise to 12,3V and the +5V lines turn to 4,93V.

Yes after looking at it, the audio capacitor's item number is: XPP-3.9-250 but its description never stated this to be a problem. Is it? The old capacitor stretched the same way.

 

[MacTech68]

Seems that convention is to use Panasonic ECW-F2395JA or similar.

Have you replaced these two circled caps ?

 

[Retro collector]

So isn't that good XPP-3.9-250?

Yes, I replaced it.

 

[MacTech68]

It's the handling of peak AC & HF that worries me.

If the original looked like this:

Then it was probably ok. These were the last revision of the board.

 

[Retro collector]

It doesn't look like what was originally in it, but there was a problem with the original and it works the same with the current one.

 

[MacTech68]

No problem - that one is the second last revision.

I still think that you will need to live with the problem. I'd normally expect some drift as components warm up. That's why adjustments on CRTs are usually performed after a 15min on time.

 

[Retro collector]

Can the audio capacitor stay in it? The image attached above is the original 3.9uF replaced capacitor.

I had already tried this idea, waited half an hour until the picture finally got to the edge completely (much better than the chess picture) and I wanted to adjust it that way, but then I can’t. If I put it on it stays the same until it cools down.

 

[MacTech68]

The audio capacitor may fail early, but the original electrolytic probably won't last either.

I still think it is time to get some freezer spray.

 

[Retro collector]

If I use the freezer spray during operation, will it not cause a short circuit? That's why I'm stubborn about it.

 

[MacTech68]

They should be non-conductive if specified for electronics. Check the datasheet for whichever brand you buy states non-conductive.

Use sparingly - preferably with a long reach fitted straw.

 

[Retro collector]

I think I should look at the resistors and diodes if they're getting hot or not. If they are getting warm then it may be a sign of a short circuit or a faulty component. If we look at transistors, they naturally get warm, where the freezing spray evaporates immediately.