MacSE analog board issue – squished video, flyback overheating

[CamInTosh]

Hi everyone, lot of info I'll try to break down. This is a new acquisition I've had for about a month now.

Current Problem

• Screen shows lightning/static, then suddenly compresses and darkens (“squish”) – see video and photos.
• Now: no picture, burning smell around flyback.

Hardware

• PSU: Astec AA13800
• Analog Board: 820-0206-B (630-0147-C)
• Flyback: 157-0042A
• Logic Board: 820-0176-B

History / Timeline
1. Initial work

• Reflowed analog board connectors (per Adrian Black - but I'm reading the reflow tequnique may not be the most effective).
• Replaced logic board battery with CR2032.
• No obvious signs of corrosion / broken traces on analog board, logic board, or PSU
• Mac booted, showed 1 MB RAM (correct), then I shut down awaiting keyboard/mouse and memory upgrade.
• Ordered 4 × 1 MB / 80 ns RAM from Apple Rescue of Denver.

2. Upgrade

• Installed 4 MB upgrade, clipped R35.
• Booted fine, via BlueSCSI, reported 4 MB, ran programs successfully.

3. Failure

• The next or second boot: static/lighting effect -> squished/dark screen (see video/pic).
• Attempted PSU reflow (per Larry Pina: T1, T2, L7, D4, Q2, Q3). Some joints wouldn’t cooperate, but otherwise "looked" okay.
• No discoloration near T2.
• Result: still squished/dark display.

4. Troubleshooting

• Mac still chimes, mouse works.
• Measured voltages at HDD connector: +5.05 V, +11.94 V (under load).
• Reverted back to 1 MB RAM (re-soldered R35). Thought maybe extra RAM triggered video issue.
• Same problem, though the squished image looked a bit clearer on 1 MB.
• Left Mac running briefly to get my phone -> came back to hot burning smell and an auto-reboot (I heard the chime).
• Flyback cage extremely hot, electronics burning smell in the air, air around flyback was hot.

Next Steps / Questions

• Suspect failed flyback (157-0042A) maybe?
• None of the caps on the analog board appear damaged or bulged.
• I'm willing to desolder/resolder/test/replace parts as needed. I just didn't want to shotgun every component blindly without asking for advice!

Thank you!
-cam

 

[JDW]

The BU406 (Q2) mounted to the metal cage is the usual suspect. Could be CR2 as well. See pages 51-52 in the following Larry Pina book:

Mac classic & SE : repair and upgrade secrets : Pina, Larry : Free Download, Borrow, and Streaming : Internet Archive

Includes index

archive.org

 

[Kai Robinson]

The BU406 (Q2) mounted to the metal cage is the usual suspect. Could be CR2 as well. See pages 51-52 in the following Larry Pina book:

Mac classic & SE : repair and upgrade secrets : Pina, Larry : Free Download, Borrow, and Streaming : Internet Archive

Includes index

archive.org

The pdf is in the resource section.

 

[JDW]

The pdf is in the resource section.

In the Resource section, I cannot find the "Mac Classic & SE" book that I linked in my previous post, but I do see these "related" PDFs...

https://tinkerdifferent.com/resources/apple-technical-procedures-macintosh-se-and-macintosh-se-30.66/

https://tinkerdifferent.com/resources/macintosh-repair-upgrade-secrets-for-models-128k-to-macintosh-se.42/

https://tinkerdifferent.com/resources/the-dead-mac-scrolls.20/

Here's a photo of the three Pina books I have physical copies of...

 

[CamInTosh]

I'm so embarrassed... I have all of the PDFs mentioned, but I was in "panic mode" and decided to reach out before consulting the books! But I also prefer the extra personal confidence from talking to people!

Having said that, I see what Larry is saying about Q2 and CR2. To me, the last paragraph reads like: "while you're in there, replace CR3 and CR5 as well" since they are both linked, in someway, to Q2. I'll source those 4 parts.

I hope to have an update by next week-ish.
Thank you!