Mac Plus Repair

[arcademan0]

So, I have an old Mac Plus I'm trying to fix. I have an idea on what the problem might be but I want the opinion of someone who knows what they're doing. I'm pretty sure the problem is the flyback transformer but I think there might be more to it than that. When I turn on the computer there is no startup bong, the screen is blank, there is a high pitched whirring, after 20 seconds there is an ozone smell, and the top left part of the computer (where the analog board is) gets super hot. Ideas, thoughts, advice?

 

[MacTech68]

It does sound like the flyback, and it's cooking the HOT (Horizontal Output Transistor).

I expect when you get it apart, the heatsink for the HOT will be a lovely, purple/blue.brown color.

FBT & HOT will most likely require replacement.

FBTs are horrendously expensive these days.

For example (NOT an endorsement) :

157-026C Flyback 157026C / Replaces Apple / HR 42031 | eBay

All credit cards are processed with Authorize.net. © 1982-2015 Dalbani. Serving the Electronic Industry Since 1982. Miami, FL 33166. 4225 NW 72nd Ave. Dalbani is a national and international distributor of high quality electronic components and parts.

www.ebay.com

It may work out cheaper to buy another 128, 512, or Plus and scrap it for parts.

 

[Appleinapot]

Ooh, could you send a pic

 

[arcademan0]

Ooh, could you send a pic

I'm away from the computer at the moment but I'll get you that pic in about a week.

 

[Appleinapot]

I'm away from the computer at the moment but I'll get you that pic in about a week.

Oh thanks

 

[arcademan0]

Oh thanks

Here you go, sorry it took so long.

 

[arcademan0]

Here you go, sorry it took so long.

I also noticed that this had some sort of rust on it. I think it may be a chemical reaction from the ozone and the metal on the CTR.

 

[arcademan0]

It does sound like the flyback, and it's cooking the HOT (Horizontal Output Transistor).

I expect when you get it apart, the heatsink for the HOT will be a lovely, purple/blue.brown color.

FBT & HOT will most likely require replacement.

FBTs are horrendously expensive these days.

For example (NOT an endorsement) :

157-026C Flyback 157026C / Replaces Apple / HR 42031 | eBay

All credit cards are processed with Authorize.net. © 1982-2015 Dalbani. Serving the Electronic Industry Since 1982. Miami, FL 33166. 4225 NW 72nd Ave. Dalbani is a national and international distributor of high quality electronic components and parts.

www.ebay.com

It may work out cheaper to buy another 128, 512, or Plus and scrap it for parts.

I noticed the heatsink was coated a brownish color like you said. And I found a surprisingly good deal on a flyback transformer so that's coming in on Saturday.

 

[MacTech68]

I noticed the heatsink was coated a brownish color like you said. And I found a surprisingly good deal on a flyback transformer so that's coming in on Saturday.

You'll need to replace that transistor too.

 

[arcademan0]

Just to confirm, as of right now I need to replace 2 components, the Flyback Transformer and the Horizontal Output Transistor?

 

[MacTech68]

Just to confirm, as of right now I need to replace 2 components, the Flyback Transformer and the Horizontal Output Transistor?

At the very least, yes. You'll need a small nut & bolt to attach the transistor to the heatsink (or a rivet) and some heat transfer compound).

 

[dmr727]

Stupid question, but I don't see the brownish color on the heat sink. Is that a picture thing or am I just blind?

 

[MacTech68]

Stupid question, but I don't see the brownish color on the heat sink. Is that a picture thing or am I just blind?

If you compare it to the other heatsink next to it, it should be more obvious, but I'll agree it is very slight compared to some I've seen.

The very first photo also shows a dulling of the surface for about 2/3rds of the lower portion.

EDIT: as an example, this page shows the range of colours expected at different temperatures:

What is the Heat-Affected Zone? | Gasparini Industries

www.gasparini.com

 

[Appleinapot]

I've never seen a mac plus before, it looks really cool?

 

[Appleinapot]

Stupid question, but I don't see the brownish color on the heat sink. Is that a picture thing or am I just blind?

I see the brown in one picture

 

[arcademan0]

At the very least, yes. You'll need a small nut & bolt to attach the transistor to the heatsink (or a rivet) and some heat transfer compound).

Would it be acceptable to reuse the current heatsink, nut, and bolt for when I replace the transistor?

 

[MacTech68]

Would it be acceptable to reuse the current heatsink, nut, and bolt for when I replace the transistor?

AFAIK , yes.

 

[arcademan0]

The flyback transformer came in yesterday and I soldered it in today. I turned it on and it works! I'll have to test it long term to see if the screen maintains its normal functions but so far everything looks promising. I didn't even need to replace the Horizontal Output Transistor but may need to if the screen gets wonkey.

 

[arcademan0]

All of the hardware issues are taken care of and now that just leaves the software. I've done some research and it appears the latest software version it can run is System 7.5.5. Further research has led me to believe that in order to run this software I would need an external hard disk as the mac doesn't have enough RAM to run the software by itself. It also seems I would have to install the software onto the hard disk from a different computer as the Mac Plus only has an 800kb disk drive and the installer disks are 1.4mb. Would anybody happen to know where I can get all the necessary installer files for 1.4mb floppy disk?

 

[MacTech68]

You may want to reconsider running System 7.5.

Whilst it's possible, even with a full 4MB of RAM, it doesn't leave much free for programs to run.

Yes, each owner will have their own opinion, and they vary.

In any case, to perform an installation of say System 7.1 or 7.5 would (I'd recommend) require a SCSI hard drive or even a FloppyEMU or SCSI2SD.

If you don't have the $ for the latter two, what other older Macs do you have, if any ?

 

[arcademan0]

You may want to reconsider running System 7.5.

Whilst it's possible, even with a full 4MB of RAM, it doesn't leave much free for programs to run.

Yes, each owner will have their own opinion, and they vary.

In any case, to perform an installation of say System 7.1 or 7.5 would (I'd recommend) require a SCSI hard drive or even a FloppyEMU or SCSI2SD.

If you don't have the $ for the latter two, what other older Macs do you have, if any ?

As of right now, the Mac Plus is the only mac I have.

 

[arcademan0]

So, I've noticed the screen is blinking out every couple of minutes but after I tap the computer, the screen turns back on. Is this a result of the Horizontal Output Transistor failing?

 

[MacTech68]

No. Most likely a dry/cracked solder joint on the video pin of the analog board to logic board connector.

Worth checking the soldering of all the circled connector pins.

 

[arcademan0]

So, I'll just have to reflow them?

 

[MacTech68]

So, I'll just have to reflow them?

Well, removing old solder and applying fresh new solder is preferred.