Noob trying to restore a Mac Classic. Need some help!

[benanderson89]

Hi everyone.

I'm a complete newcomer to the world of classic macs and I recently bought two (sold as not working) compact classics for peanuts from an apple repair shop here in the UK. One was beyond saving (battery exploded, tube smashed) but had a sections of good parts inside (80MiB quantum, weird RAM board with Motorola SIMS) and a brilliant case. The second of the two computers had a brilliant motherboard with almost no corrosion, but the case was junk. So I'm trying to combine the two together to make one complete machine.

I've just finished recapping the motherboard and when performing a smoke test (with no RAM Board, no FDD and HDD connected), the speaker just makes a crackling sound that gets louder the longer the machine the left on (and if the machine was on previously, it'll become louder more quickly). I'm too nervous to leave it on for long enough to see if the tube warms up and generates an image (though I'm fairly certain it wont). Anything coming out of the speaker is a vast improvement as it previously showed no signs of life, but now I'm at a loss -- I know my way around Commodores but not a Compact Mac.

Any help would be fantastic. In the meantime I'll be removing the motherboard and giving it another clean with IPA just to be absolutely sure nothing funny is left on the board.

Thanks!

YouTube Video showing the issue.

 

[techknight]

you need to recap BOTH the motherboard, AND the analog board. They are both equally as bad. 

 

[benanderson89]

you need to recap BOTH the motherboard, AND the analog board. They are both equally as bad. 

Think that might be the issue? Seems simple enough. I'll see about ordering some new caps for it soon. Does anyone sell little premade kits of all the caps needed so I don't have to hunt them all down? For some reason I remember 8-bit guy (David Murray) mentioning that in one of his videos.

 

[desiv]

I have gotten my cap kits from Console5, although that is in the US...

 

[benanderson89]

The likes of Mouser and Digi-Key in the UK want £17,00 postage for a hand-full of caps (for orders under £30-something), so I may as well buy them pre-made from Console5 if all the values are the same.

 

[erichelgeson]

I just did a console5 classic 1 recap - went well, just a ton of them! Also checkout my classic 1 restore thread (in sig) - my analog board needed a through cleaning as there were shorts from the cap gunk on it. I have a few links to some trouble shooting material in there too.

 

[benanderson89]

Thank you very much! I'll give that a read now. I don't have any capacitor gunk on my board and they don't look like they're bulging (but looks can be deceiving). Was chatting with someone else and it looks like the board isn't getting enough power, hence the clicking since it's constantly resetting, and it also explains why it was getting louder and faster as something somewhere was slowly building up the necessary voltage. I'll have to test the 5v rail once I get a battery for my multimeter tomorrow.

Is there a service manual for the Classic analogue board? I've got one but it's for the Performa 200 (European Classic II) and I'm not sure if it can be used for the Classic.

 

[benanderson89]

P.S. totally saved the link to your mouser order! Hopefully I have the same board revision.

 

[erichelgeson]

. I don't have any capacitor gunk

Mine looked ok too, but then I cleaned a bit and it showed. Then cleaned a lot more and it started working

saved the link to your mouser order

In addition to that I have all the original measurements, specs, ratings in a google doc here - https://docs.google.com/spreadsheets/u/1/d/e/2PACX-1vQ4IIm9_V-ht-noaTYUQ69uDTa02m2Z8GZHQKsP4WaBg9rQlXHsYZ6kUW_RX5F-2K7YvoxllFaBglhR/pubhtml?gid=1456052816&single=true&widget=true&headers=false

I've been documenting all my recaps and will be sharing hopefully a comprehensive list of caps, parts, kits, etc soon.

 

[benanderson89]

Yeah I really need to give the rest of the computer a dust and a swab with IPA. The motherboard has came up fab though. Now if I could only get the rest of the computer to look like this then I'll be golden.

 

[dochilli]

I would measure the voltages at the floppy port. Must be 5 and 12 V. 4.85 may also result in a booting classic. 

Classic AB have some other parts that often fail:

DP4, DP3, TDA4605, CNY17G-3

 

[dochilli]

Picture of the floppy port:

https://images.app.goo.gl/viGJ5rcLaVmtzyJ89

 

[benanderson89]

Quickly looked for a pin-out. 5v on Pin 6 and Ground on Pin 1? Asking just to be sure.

 

[cheesestraws]

Yup, you should have 5v on pin 6 and 12v on 7, IIRC.

 

[benanderson89]

You'll laugh, but the probes on my dirt cheap multimeter are too big to fit in the pin holes on the floppy connector, so I couldn't get a reading! haha.

However, some observed behaviour:

1. The speaker clicking slowly picks up speed, meaning whatever is not providing the correct voltage is slowly trickling it in, and;
   
2. I heard a very short and quiet hiss. I'm not sure if it was static build up inside the CRT or something blowing. There was no smoke so I assume the CRT was just getting charged, but there was a faint smell of something, not sure what, but it was probably dust getting burnt off the yoke.
   

After that I pulled out the hard disk so I could get a better look at the high voltage board and, lo and behold, brown cap juice!

I've got nothing to discharge the CRT with right now (I need to buy one of those ant-static wristbands), plus I'm technically at work, but later on today I'll be able to remove the board and start de-soldering the old caps and cleaning everything up.

How do you tell if a power board is Rev A or B? My board is stamped with the model number 805-0993 B, but it doesn't match any part number in the official apple service manual (Rev A and B 220v boards are 661-0599 and 661-0652 respectively). If it's a Rev A board then I can order erichelgeson's Rev A kit from mouser -- if it doesn't matter and the values are the same between both boards then I'll just order them anyway.

 

[cheesestraws]

You'll laugh, but the probes on my dirt cheap multimeter are too big to fit in the pin holes on the floppy connector, so I couldn't get a reading! haha.

Mine are the same.  I use two bits of solid core wire, one end bent around the multimeter probe and one end in the socket.

 

[bibilit]

How do you tell if a power board is Rev A or B

Classic are mainly Rev A.

Rev A boards have a thick connector with a locking tab, Rev B is thinner without the tab

 

[benanderson89]

Then I'm sure I have Rev B if it's the yoke connector you're talking about.

 

[bibilit]

Right.

So either a very late unit or a swap at some point.

Late units share the same rear casing with the Classic II (a blanking plate was supplied for the microphone) but holes were present for the speaker on the side.