Macintosh Plus - Analog Board Clicking

[Stephen]

A few months ago I bought an analog board (PN: 630-0102-J) knowing it did not work. I was hoping it could be resolved with a good cleaning, fresh caps, and maybe some reflowed solder joints but alas — here I am.

• I have replaced all of the caps
  
• I have reflowed all of the solder joints (yes all of them)
  
• I have cleaned the board
  
• I have inspected almost all of the resistors and confirmed they are within tolerance.
  
• I found R11 was corroded and replaced it.
  
• I've confirmed the (very old) transformer still works by installing it in a working Macintosh Plus analog board.
  

Never the less, it repeatedly clicks / squeals (video) in the same way it did before I started working on it. Does the wisdom of the 68K Macintosh Liberation Army have any advice or is my analog board officially a donor board? 

 

[Crutch]

You didn’t mention it, but I assume of course you have confirmed the voltage level is correct/adjusted it with the pot.

Have you checked The Dead Mac Scrolls?  p. 39 “The computer makes a high-pitched chirp chirp chirp noise” —> replace the barrel rectifier at CR5, he says.  But there are other symptoms in there that could plausibly match what you’re seeing also.

https://archive.org/details/mac_The_Dead_Mac_Scrolls_1992

 

[Stephen]

You didn’t mention it, but I assume of course you have confirmed the voltage level is correct/adjusted it with the pot.

Have you checked The Dead Mac Scrolls?  p. 39 “The computer makes a high-pitched chirp chirp chirp noise” —> replace the barrel rectifier at CR5, he says.  But there are other symptoms in there that could plausibly match what you’re seeing also.

https://archive.org/details/mac_The_Dead_Mac_Scrolls_1992

Thanks for the tip, I'll check it out. Anyone have concerns about using this rectifier (1N4937GP-E3/54) as a replacement? I saw it mentioned on jagshouse.com. 

 

[desertrout]

The usual replacement part for CR5 and CR1 is this one https://www.mouser.ca/ProductDetail/Vishay-General-Semiconductor/EGP51G-E3-C?qs=%2Fha2pyFadujcYTdXhGCQYso42sonLqjMPlByH43PYaA%2F7QQpIoSejQ%3D%3D

That jagshouse link is for the SE/30 which has a different analog board than the 128k/512k/Plus.

 

[desertrout]

I'd also recommend Pina's 'Repair Secrets' (http://www.maccaps.com/MacCaps/Repair_books_files/Macintosh Repair and Upgrade Secrets.pdf) for a solid overview of the Plus, and includes good info on some of the typical adjustments / benchmarks to check for when troubleshooting a Plus AB. First thing, as Crutch says, is check voltages, and check if you can adjust +5V with the voltage pot. Sometimes after recapping you need to dial it down. This is also a decent resource: http://www.maccaps.com/MacCaps/DIY_Information_files/Classic Mac Repair Notes .pdf

 

[Stephen]

I took a few days away from this — the replacements parts removed the click but now I get nothing at all! I'm including my list of replacements if it's of any help; the purchases were based on common problems from the dead mac scrolls and their modern equivalents.

If someone is more experience and willing to repair this analog board (US) and another (International), I'm interested! In the meantime I am also open to more experienced suggestions to debug this further. 

 

[desertrout]

Sometimes it's just how it goes - replace a couple components, and it reveals weaknesses elsewhere in the circuit. A high res pic of the board may help here - always good to check if the components are installed in the correct orientation (it happens).