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PotatoFi

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18 hours ago, Jinnai said:

d-did you get a capacitor backwards... the weird thing here is that it used to kind of work....

How DARE YOU! You think that I, the Great Potato, would install a capacitor backwards?! I am so offended right now. SO offended.

 

...but seriously. Yes, I might have. I tried very hard to NOT do this, but it is possible. I think tonight or tomorrow, I'll take it back apart, discharge the CRT, pull the analog board, and carefully check for polarity issues. I'll also snap some pictures of the anode connector and post them here - I'm still wondering if I bent something there, and that is the culprit.

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Home from a business trip and had components waiting. Here's what happened:

  • Checked for backwards capacitors, everything looks good
  • Replaced caps C2 + one more that I can't see now that it's back in the computer
  • Replaced CR21 Schottky barrier with an MBR360 rectifier (per Dead Mac Scrolls page 22)

After those steps, the behavior has definitely changed. The flup-flup-flup (the sound of a CRT monitor turning on repeatedly) is quieter now, but still there, and each flup happens about 1/3 a second. So 3 flups per second. The display is dark. There are no other sounds. The "flup-flup-flup" does not speed up or slow down. It also isn't as terrifying.

  • Turned voltage all the way counterclockwise (per Dead Mac Scrolls page 27)

Floppy port 5v measured between 0.25v and 0.4v. The "flup-flup-flup" is a tiny bit slower now.

  • Turned voltage almost all the way clockwise

Floppy port 5v measured between 0 and 4.0v

  • Checked for blue wire continuity between the analog and logic boards (per Dead Mac Scrolls page 26)


Mods, do you think we need to move this discussion over to the Compact forum? I didn't anticipate this much troubleshooting. Also, I am running out of ideas REALLY fast.

Edited by PotatoFi

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The flup flup is a symptom of the power supply trying to kick in.

 

I solved a lot of those on Pluses replacing the optoisolator (a small chip near the brightness knob on the A board, labeled U3 IIRC ) those fail a lot.
 

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9 hours ago, bibilit said:

The flup flup is a symptom of the power supply trying to kick in.

 

I solved a lot of those on Pluses replacing the optoisolator (a small chip near the brightness knob on the A board, labeled U3 IIRC ) those fail a lot.
 

Thanks for the tip! Is there any way to test it? Have you seen this symptom resolved by replacing the optoisolator? I'm worried that I'm starting to just replace random parts instead of troubleshoot.

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Hi, no there is no way to test it, but i have fixed a lot of them with this symptom.

 

I you have another board you can do a swap for a test, in the Plus this part is socketed, even can use one from a Classic, not the same reference but works the same.

 

Don't remember but the part is pretty cheap anyway.
 

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On 3/27/2019 at 10:48 PM, PotatoFi said:

The very last step is to install the anode cap, but... while the metal parts inside the cap seem to be holding tight, I can't get the suction cup to REALLY suction down. It un-sucks after about 60 seconds. Is this a problem?

You are correct in calling it a “anode cap”. 

It is not a suction cup. It’s there to keep the 10,000 volts in. 

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Sadly, replacing the optoisolator/optocoupler did not fix the problem.

On 4/5/2019 at 10:46 AM, bibilit said:

There is a fuse also in the loom connecting LB to AB, is this ok ?
 

Is this the glass tube fuse very near the power plug and filter? If so, yes it is good, I tested it for continuity.

 

Ok, that is all of the ideas that I had. Other than find a replacement Analog board, which would be a shame as this is a 128k board and almost all of the caps are new.

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I don't have much experience as my Plus only needed a ram replace, but my 128k came from a guy who replaced the analog board due to a bad flyback transformer. Now, I know that these flyback transformers are known to go bad so I wouldn't be surprised if that was causing your issue. If this is the case, then the flup noise could be the flyback repeatedly arcing internally.

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Page 24 of the Dead Mac Scrolls also says to replace component CR20 on the board, right next to CR21. This component is an MBR1045 Schottky Rectifier Diode. In fact, pages 20 through 29 deal with this issue entirely. You didn't mention these steps so I thought I should point them out. Also, if you deduce that the flyback is the issue I could possibly send you one.

  

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13 hours ago, MacAttack said:

Page 24 of the Dead Mac Scrolls also says to replace component CR20 on the board, right next to CR21. This component is an MBR1045 Schottky Rectifier Diode. In fact, pages 20 through 29 deal with this issue entirely. You didn't mention these steps so I thought I should point them out. Also, if you deduce that the flyback is the issue I could possibly send you one.

  

Thanks for chiming in here @MacAttack, I'm feeling pretty stuck on this and appreciate the help.

 

The Dead Mac Scrolls has been my #1 resource for this Macintosh Plus project, but I think there's a big gap in my knowledge around how to test for in-circuit resistance. I did test CR20, but I didn't really understand what setting to use on my multimeter (200, 2000, 20k, 200k, or 2000k), and I didn't understand what 31 Ohms/30 Ohms meant. Is that a range of resistance, is that a 31 or 30 statement? Just not sure.

 

If I remember correctly, resistance was at about 100, but steadily dropped to 35 or so during a few minutes (it took some time to fall to the "correct" amount). So yeah, NOT confident that I did troubleshooting properly.

 

In addition, I'm not finding the MBR1045 in the correct axial formfactor. If anyone has advice on locating the correct part I would appreciate it - I've been using Arrow.com for components because they have free 2-day shipping.

 

Many thanks for the hand-holding on this... I want to see this Macintosh Plus live, and I'd really like to preserve the analog board.

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On 3/3/2019 at 9:18 PM, PotatoFi said:

Everything seems to work, but the display is dark. On the SE it turned out to be a broken leg on a filter.

Do you have details? I have an SE here that is the same. Resoldering J1 did no good. Where was the filter?

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4 minutes ago, beachycove said:

Do you have details? I have an SE here that is the same. Resoldering J1 did no good. Where was the filter?

For my Macintosh SE FDHD, it ended up being a broken filter near J1. It was the dumbest thing! The filter is susceptible to being broken off when removing/installing the analog board (it basically touches the CRT). Details here:

Keen to discuss your SE more, let's pick up the conversation in the SE No Video No Raster thread!

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