[HELP] Macintosh Plus Checkerboard screen

[LaPorta]

I'm certainly not belittling your work here, but, are you sure that C1 equivalent is tolerating this? Those things look awfully small and tiny.

 

[Shymon184]

I'm certainly not belittling your work here, but, are you sure that C1 equivalent is tolerating this? Those things look awfully small and tiny.

No offence taken  but this is why I did it:

[SIZE=12pt]A suitable replacement capacitor can be a little difficult to locate on occasion, however, so if you don’t mind altering the appearance of the board, you may substitute a parallel combination of four or five 1[/SIZE][SIZE=12pt].0μ[/SIZE][SIZE=12pt]F ceramic disk capacitors, rated at 50V breakdown or more (there’s plenty of room; build it up as a module of four caps, and use two pieces of bus wire to connect it to the pc board; secure with hot glue if you wish). Ceramic capacitors are readily available and inherently nonpolar. What’s more, the parallel combination reduces the overall ESR to lower values than the commonly suggested replacements. Plus, whatever heat they generate is now spread out among the separate capacitors, reducing still further any temperature rise. This somewhat un-aesthetic solution is extremely robust.[/SIZE]

This is written in Classic Mac Repair Notes 2.

 

[Shymon184]

I am afraid that the T3 transformer is actually melting, here are the pics:

I don't need circuitry knowledge to see that it really shouldn't be in this shape, also the bottom terminals in the first picture seem awfully fried/burned.

 

[LaPorta]

Granted, yes, Pina has said that will work. I just thought it was multiple points of failure that could go wrong. Maybe it works great!

As far as the transformer, I am no expert on this, but they are all coated in that goop. That looks pretty standard for all the boards ive seen. Doesn't mean it might not be bad.

 

[Shymon184]

Granted, yes, Pina has said that will work. I just thought it was multiple points of failure that could go wrong. Maybe it works great!

As far as the transformer, I am no expert on this, but they are all coated in that goop. That looks pretty standard for all the boards ive seen. Doesn't mean it might not be bad.

That might be true, but let's be realistic, the material seems like plastic and if you look at the analogue board pictures above, you can see the other corners look alike, but the bottom left corner is out of shape, this leads me to believe that it was made to handle certain amount of heat and on that one corner, the amount of heat exceeded the operating temperature and it just melted. So something happened that should not happen normally.

 

[LaPorta]

Techknight should be able to weigh in here more definitively.

 

[LaPorta]

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

 

[techknight]

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. 

 

[Shymon184]

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.  :-/

 

[Shymon184]

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.

 

[Daniël]

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?

 

[techknight]

Yup those

 

[Shymon184]

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.

 

[techknight]

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.