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Shymon184

[HELP] Macintosh Plus Checkerboard screen

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That transformer is epoxy resin dipped. Its fine. 

 

and if I recall, I think it was the international version people were having issues in those thread. Jeez, I need to go digging for the threads. 

 

If the transformer was bad, it would blow the fuse in short order. and destroy its accompanying chopper transistor. 

Edited by techknight

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8 hours ago, LaPorta said:

Just for comparison, here is a photo in one of my threads of someone else's. Not zoomed in, but you can see the general shape:

 

https://68kmla.org/forums/index.php?app=forums&module=forums&controller=topic&id=60138&do=findComment&comment=643539

Well, there’s no bulge in the bottom left corner in that picture, but techknight said it’s fine, so I guess that’s the end of my concerns. I still don’t like the shape though. :-/

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8 hours ago, techknight said:

That transformer is epoxy resin dipped. Its fine. 

 

and if I recall, I think it was the international version people were having issues in those thread. Jeez, I need to go digging for the threads. 

Ah, if you could find them, I think it would be a useful help for my problem.

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17 hours ago, techknight said:

 

No, it is most certainly NOT normal. Voltages should climb up nearly instantly and remain steady at all times. There are many things in this power supply known to cause issues, and I remember running into a handful of threads where stability issues were being caused by a specific component that other members were trying to find functional substitutes for. I forget which threads they were, its been years. 

Those were the threads on the E0102 stuff, right?

 

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I am afraid that this isn't much use to my problem, because in the Mac 128K topic, the analog board was used on a wrong voltage, which doesn't apply to my case because I have international board; mine was made to be used on 240V. The Mac Plus topic concerns a burned transistor, which also might not apply to my case because I checked my transistors after reading the topic and they are not burned at all. I guess I shouldn't be so certain about irrelevancy of these two topics, but it just doesn't seem to me like they are applicable to my problem. My theory is that a component of the power supply is half-dead due to heat or age, therefore causes the voltage fluctuation when cold (since the checkerboard disappears when the voltage gets stable), yet the component isn't functional enough to produce sound. Based on this, I think the component or components are a part of power supply circuit and audio circuit. My theory might be wrong though, for I don't fully know how the Macintosh operates.

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The trouble with speculation and theories, its not going to solve the problem. 

 

I pointed to those threads because it may contain relevant information to start looking at for troubleshooting the power supply to discover the real problem. Just because the cause was different in their case, Doesn't rule anything out. 

 

In the end, only electronics troubleshooting and tracing/repairing will solve this problem. 

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