Macintosh Plus White bars issue

[SnooperSmokio]

I recently bought a Macintosh plus, and when I tried to power it on. It gave me white bars and a strong buzzing noise coming for the speaker, I pulled out the Logic board and cleaned it over with Alcohol. After wards I reseated the 4mb of ram and the ROM chips. All capacitors on the analog board appear like they are brand new, so they aren't the issue. Any help would be appreciated, Cheers.

 

[dochilli]

- Check the connector to the screen on the analog board. The solder is often cracked. Resolder the connector. Sometime the same happens to the board on the tube.

- Give the side of the case with the analog board a little clap with your hand. Perhaps the screen will work then. Sometimes this works when the solder points are cracked.

- Resolder the flyback.

- Could be a problem with the RAM.

 

[bibilit]

Can be a problem with Ram (you can test with another set) Rom also, but only happened to me once.

 

[SnooperSmokio]

I'm confident that the screen and analog board are fine, I also see no cracked solder joints. I'm going to order some new ROM Chips and RAM sticks.

 

[Bolle]

Screen and CRT section on the analog board are obviously fine (at least good enough to give you a full raster)

You are having a logicboard issues here. As bibilit said I would start by trying another set of RAM or a different combination of the sticks you got in there right now and see if the pattern on the screen changes.

Also check if 5V/12V supply to the logicboard is within spec.

Does the buzzing noise disappear or does it continue to make the same noise as long as it is powered on?

 

[Zippy Zapp]

I wouldn't dismiss the capacitors so quickly.  They can look clean and not bulged but still be out of spec or shorted dead.  I have never had one of these to repair but my understanding is there is a lot of heat generated from the analog board and the life of those caps are shortened because of that. 

That said, voltages should be something to check.  

This video shows a Classic II but the screen looks similar (caused by caps):

https://youtu.be/mBnQXqRjrCc

Of course, the Classic used SMD caps and they are much more likely to leak then the 30 year old through-hole caps in the older Macs.

 

[CharlieFrown]

I've had many Pluses and none of them required recapping. Those THT caps are likely to outlive us. 

I am 99% sure it's a ROM related issue.  I've had  the same pattern on my Plus without ROM chips.