[HELP] Macintosh Plus Checkerboard screen

[Shymon184]

My Macintosh Plus has many hardware issues, but I would like to address this one today. This checkerboard appeared one day and alongside that, the sound stopped working. I already replaced electrolytic capacitors on both logic board and analogue board. I recently upgraded my Macintosh from 2.5Mb of RAM to 4Mb of RAM and the checkerboard changed. I would appreciate some help with this problem because I tried many solutions and none have worked.

Before 4Mb upgrade:



After 4Mb upgrade:

 

[LaPorta]

Have you tried re-seating the ROM chips?

 

[Shymon184]

Have you tried re-seating the ROM chips?

Indeed I tried, I also cleaned the metals with alcohol.

 

[LaPorta]

Have you checked continuity of the actual pins for the sockets as well? That could also possibly do it.

 

[Shymon184]

Have you checked continuity of the actual pins for the sockets as well? That could also possibly do it.

Yup, I checked the pins before installing the 1Mb sticks, they seemed fine to me, all lined up perfectly.

 

[Shymon184]

I forgot to mention that the checkerboard screen disappears after few seconds and normal boot sequence occurs. Other important thing is that if I select "Restart" in the Special menu, there's no checkerboard when the Mac restarts. This leads me to believe that this issue is not related to RAM per se.

 

[LaPorta]

That would point to some sort of loose or poorly soldered connection that improves when the machine heats up. You could try and find it, or what’s probably easier is just resoldering all of the socket pins. Also, make sure that the socket fingers are making good contact with the RAM sticks.

 

[Shymon184]

That would point to some sort of loose or poorly soldered connection that improves when the machine heats up. You could try and find it, or what’s probably easier is just resoldering all of the socket pins. Also, make sure that the socket fingers are making good contact with the RAM sticks.

Resolder the logic board? That's a no no for me, I can barely resolder the analogue board, I guess I'll have to find someone who's gonna do the job...

Also other weird thing that happens with the picture is that over time, the picture just becomes wider, you can't see it expanding, you will only notice it when you use the Mac for a few minutes. Any pointers for that?

 

[techknight]

Or, the voltage is low on your analog board, 

 

[Shymon184]

Or, the voltage is low on your analog board, 

That is more likely I think, but I can't quite figure out what went wrong, I adjusted the voltage to 5V and nothing has changed. Maybe the high voltage power supply is failing (I read something along those lines in Macintosh Repair and Upgrade Secrets or Classic Mac Repair Notes, can't remember which).

 

[techknight]

high voltage power supply wouldnt have anything to do with this. 

Big thing is making sure the 5V, 12V, and -12V voltages to the logic board are on target. 

 

[Shymon184]

high voltage power supply wouldnt have anything to do with this. 

Big thing is making sure the 5V, 12V, and -12V voltages to the logic board are on target. 

Like I said, I adjusted it, but I can check again...

 

[Shymon184]

high voltage power supply wouldnt have anything to do with this. 

Big thing is making sure the 5V, 12V, and -12V voltages to the logic board are on target. 

I checked the voltage and I got these results:

• Upon startup the voltage (both 12V  and 5V) started fluctuating, the 12V ranged from 9.n/aV to 12.08V and the 5V never went below 4V and for a second was 5V.
  
• Once the Mac got to the insert diskette screen, the 12V stayed on 12.08V and the 5V stayed on 4.98V (which is strange because I adjusted it to 5V a few months ago).
  

 

[techknight]

And there is your problem. You still have power supply issues that you need to Iron out. 

 

[Shymon184]

And there is your problem. You still have power supply issues that you need to Iron out. 

So, you're telling me that fluctuating voltage isn't normal? Well that's a start, now let's find the problem! What could go wrong with the power supply?

I'm no expert in electrical circuits, but my tip is on the T3 transformer, last time I checked, it looked kinda fried up.

 

[techknight]

So, you're telling me that fluctuating voltage isn't normal? Well that's a start, now let's find the problem! What could go wrong with the power supply?

I'm no expert in electrical circuits, but my tip is on the T3 transformer, last time I checked, it looked kinda fried up.

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. 

 

[Shymon184]

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. 

> I forget which threads they were, its been years.

Oh well, that's unfortunate, but at least I know what's wrong with my Mac. This narrows down the list of possible problems a lot, so thank you very much.  )

I'm reading The Dead Mac Scrolls at the moment and a lot of symptoms (especially the audio ones) point to the flyback transformer. I'm gonna do more research now.

 

[davidg5678]

I'm reading The Dead Mac Scrolls at the moment and a lot of symptoms (especially the audio ones) point to the flyback transformer. I'm gonna do more research now.

The Flyback Transformer is a high voltage component. This is powered by the lower voltage PSU which sounds like it is broken. I think that you need to fix the power supply before doing anything with the Flyback Transformer. At a minimum, I would recommend thoroughly inspecting the components on the PSU and looking for anything that looks burned up. Of course, this might not be the case, and something could be broken without looking different from normal. Are you able to post some pictures of the Analog Board?

 

[Shymon184]

The Flyback Transformer is a high voltage component. This is powered by the lower voltage PSU which sounds like it is broken. I think that you need to fix the power supply before doing anything with the Flyback Transformer. At a minimum, I would recommend thoroughly inspecting the components on the PSU and looking for anything that looks burned up. Of course, this might not be the case, and something could be broken without looking different from normal. Are you able to post some pictures of the Analog Board?

Sure, here are some pics:

It's an International analogue board btw.

Ignore the C1, it's an equivalent replacement and it also handles the heat a bit better. 

P.S. if you want any specific pics, don't hesitate to ask.