Mac Plus power supply.

[rocket-dog]

Hello!

Has anybody here replaced the internal power supply with an external one? Does anybody foresee any problems with undertaking this venture? Would two power supplies, one for screen and one for the logical board, be a good approach?

My recently purchased Mac Plus is in an OK condition (no screen etching etc.) apart from the power supply overheats resulting in a dead screen or perhaps worse! This is I know a common problem with the design due to the lack of an internal fan.

The Mac I feel is too good to scrap (for parts!) so I would appreciate any advice on what to do next.

 

[tomlee59]

The first thing to do is to verify that the Plus' problem is indeed only with the power supply, and not with other parts of the analog board. If the problems are truly limited to the power supply portion, then substituting a third-party supply should be straightforward, although a bit messy. See http://68kmla.org/files/classicmac2.pdf for some hints on how to troubleshoot the more common analog board afflictions, as well as for pinouts that might be of assistance in performing the surgery you propose.

Good luck!

 

[sambapati87]

If you're sure its overheating, why not rig up a fan in there somehow?

 

[JDW]

You would lose the "compact" nature of the classic Mac you own, and I doubt whatever external PSU you find would be considered anything close to beautiful.

So why do it?

 

[Bunsen]

Get as much dust as possible out of the innards of the machine, including the power supply. Use all necessary electrocution precautions of course.

Consider a Kensington System Saver - a self powered fan in a box that sits in the well on top of the Mac. You could probably make something like that yourself that wouldn't be too ugly.

I've also considered using one of the MiniITX DC-DC power supplies. That way most of the power conversion (and thus heat) is done outside (the AC to 12V DC converter). As a side benefit, you end up with a Plus you can use in the car

 

[JDW]

I agree that swapping out the PSU with another INTERNAL replacement would make sense, but having something external seems silly to me.

But I've also commented on this subject in the past, with regard to the SE/30:

http://68kmla.org/forums/viewtopic.php?p=2472#2472

Specifically, I discussed with Tom Lee about the need for separate, isolated +12v lines off the replacement PSU in order to drive the Sweep and hard drive without generating noise on the CRT. On a Plus or earlier, you wouldn't have to worry about an internal HD as they don't support such, but if you were to use +12 for something other than Sweep, I would expect the situation would still apply to you; namely, that you would need two isolated +12v outputs from whatever PSU you choose. That's not to say it "wouldn't work" with only a single +12v. But two isolated outputs would eliminate noise on the CRT.

 

[tomlee59]

My guess is that the OP's problem isn't actually the power supply. The symptoms seem more consistent with a problem elsewhere on the analog board, and so using an external supply (which I interpreted -- rightly or wrongly -- as meaning "separate from the original" and not necessarily one that lives outside of the case) may not solve anything. Need more data...

 

[rocket-dog]

Hello! Thanks everybody for your suggests both technical and philosophical.

I agree moving the PSU outside will dent the Mac's compactness and that would be a shame. But it would free air space in the case and because he/she/it is rather elderly, he/she/it won't be moved apart from dusting. The Mac still looks wonderful even if its/his/her case in now yellow(ish) with age. (A platinum case SE would look even better........)

Does this mean you guys consider the Mac mini not so mini with its external power brick?

The Mac was on for about two hours when the fail occurred. On the right hand side the case was very, very warm to the touch.

Anyway I would like to open up he/she/it anyway because I have another 2Mb of RAM to install.

I shall check out the links.

Thanks again.

 

[JDW]

Does this mean you guys consider the Mac mini not so mini with its external power brick?

I use a G4 Cube as my main OS X machine and it too has a PSU brick. But in the case of my Cube, I have the space to hide the brick. But on the little table where I have my compact Mac, I have no nice place to hid such a brick.

So it all depends on your situation. Even so, the Mini and Cube were made to use a brick, the compact Macs were not (something that matters to the purists among us, myself included).

 

[tomlee59]

The Mac was on for about two hours when the fail occurred. On the right hand side the case was very, very warm to the touch.

Thanks again.

The right hand side? Is this when viewing the mac normally? The right side shouldn't get hot...

When it "overheats," does the Plus stop functioning altogether, or is it that the display goes dark? For instance, after it fails, does it respond appropriately to the insertion of a floppy (for example)?

And does the Plus always work fine after you give it a chance to cool off?

 

[rocket-dog]

Does this mean you guys consider the Mac mini not so mini with its external power brick?

I use a G4 Cube as my main OS X machine and it too has a PSU brick. But in the case of my Cube, I have the space to hide the brick. But on the little table where I have my compact Mac, I have no nice place to hid such a brick.

So it all depends on your situation. Even so, the Mini and Cube were made to use a brick, the compact Macs were not (something that matters to the purists among us, myself included).

Thanks! I was only joking............

 

[rocket-dog]

I realized I said right when I meant to say left about the second my internet box powered down. The only mitigation I can offer is that the Mac sits on shelf with the screen to the wall, hence the left hand side becomes the right hand side. I get a bit self-conscious posting which makes me a bit a nervous and prone to mistakes resulting in a rather disjointed text. Sorry again.

When the Mac failed the screen brightness was turned way down. It was when I began to turn the brightness back up to viewing levels that I realised that something was wrong as the screen appeared to be dead. There was no picture it was completely dark.

To be honest I haven’t dared to power the box up until I had got some sens of what may be wrong. But as you have been so kind as to take an interest I will get the Mac down off the shelf now and see what happens.

If you don't hear from me again I have either been electrocuted or burned to death............

}

 

[tomlee59]

Then it sounds as if your problem isn't so much overheating as it is the standard set of compact-mac ailments. Take a look at the classicmac doc I linked to earlier. It covers how to fix the most common problems. I doubt that you'll need to shoe-horn a power supply into the thing. Fixing what you have will take much less work.

 

[Charlieman]

The right hand side? Is this when viewing the mac normally?

Definitions... As with cars, right and left side should come with the proviso "when viewed from the front". Alas with a compact Mac, all repairs are conducted from the rear. So everything on right of the the logic board when on the bench is on the left when you slide the logic board out...

 

[rocket-dog]

Hello!

I have had the Mac out on the bench. Screen is as black as night. I had ear my to the case (heck works with engines!) and I heard two noises. First there were a few faint metallic ticks and then what I think I could term "CRT" whistle (but no louder than normal for a screen of its age.) I shall print off repair doc that you recommended so that I can give a good thorough read; even after all these years I still don't like reading things off a screen.

Well I knew the risks when I bought it/him/her.

Thanks again to all of you.

 

[tomlee59]

The right hand side? Is this when viewing the mac normally?

Definitions... As with cars, right and left side should come with the proviso "when viewed from the front". Alas with a compact Mac, all repairs are conducted from the rear. So everything on right of the the logic board when on the bench is on the left when you slide the logic board out...

Point well taken! "Normally" was an unfortunately vague choice. I should've said "...when viewing the Mac as in normal use..." or some such thing.