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GroovyDrifter

Trying to repair a Classic II

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Hi!

 

I've spent today's afternoon trying to repair a Classic II that I had in my "to-do" list. I bought it as a non-working unit from UK a year ago, and as the seller said, it did not work, at all: no HD turning , no fan, no screen, no chime, nothing, nada. I opened it then and the pram battery was completely depleted, but had not leaked so I removed it and stored the unit.

 

Until this afternoon, that I decided to try and repair it. First of all I removed all the capacitors from the motherboard and reeplaced them with trough hole ones that I had handy. I addapted them cutting the legs short and building a sort of SMD leg wit my pliers.

 

After removing the capacitors and before soldering the new ones I washed the board with a toothbrush, first with very diluted cleaning vinager, to reduce the capacitor's leakage and then with soapy water. Dried the board in a dryng oven (I built it to dry paint on scale models, it keeps a temperature of 60ºC-70ºC for as long as you need) and then cleaned the pads and soldered the new capacitors. I also put a new pram battery.

 

Here are some photos:

 

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After all this work the improvement was noticeable... Still not working but when it was switched on the fan started to turn almost immediately.

 

I measured the voltages at the SCSI drive connector and the were quite low, 10V on the 12V rail and 4.3V on the 5V one. I then unplugged the floppy drive and the screen switched on with a very fuzzy and clicking image... Monitoring the 5V line, the voltage increased a little to 4.47V and whenever it reached 4,5V the power on chime sounded and a little after the checkered bacground was visible(I think it was, the image is very fuzzy and moving). Immediately the voltage dropped and stays like this until you power it off.

 

So any help will be wellcome. I'ts my first repair on a compact mac so I'm scared of being zapped tryng to remove the analog board, I'm more a 5V guy, hehehehe Do you think I should re-cap the analog board? Any non-polar electrolytic capacitors in this one? 

 

I will like to touch the analog board as few times as possible, so do you reccomend replacing the optocoupler and the switching transistor too? Can someone provide a reference of those parts? 

 

I've done some repairs on Atari power supplys, and one part is usually replaced too is the rectifier bridge, all silicon parts tend to age so why not, and I usually fit a more capable one (and a more capable switching transistor too). Do you also replace the rectifier bridge?

 

I've not found any schematics so I have to ask everything, sorry...

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Edited by GroovyDrifter

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The usual.  Zap the screen and disassemble after that.  A favourite is to run the machine with brightness on full, and pull the cord out to suck as much residual energy as possible.  I thought the newer models had a circuit that drained out the residual, but you can never be too careful.

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There is a voltage adjustment on the Classic analog board labeled PP1. I think the Classic II board is the same. I can't remember which voltage is derived from which, but adjusting PP1 will adjust one voltage and the other follows. If adjustment doesn't bring both voltages within spec, you'll likely need to recap the analog board.

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There is a voltage adjustment on the Classic analog board labeled PP1. I think the Classic II board is the same. I can't remember which voltage is derived from which, but adjusting PP1 will adjust one voltage and the other follows. If adjustment doesn't bring both voltages within spec, you'll likely need to recap the analog board.

 

I've read that it adjusts 12V and 5V is derived from that. If it's so, it's the same than the Atari power supplies, good.

 

Hi,

 

Never had an issue, leave it for a while, will be fine.

 

Yes, capacitors in the Analog board are the issue of having low voltages.

 

here are the common units to replace.

 

http://maccaps.com/MacCaps/Capacitor_Reference/Entries/1990/10/15_Macintosh_Classic_Analog_Board.html

 

I've (finally) found the Apple security bulletin wich describes how to safely discharge it (and where to ground the wire to not damage the logic board). I'll probably build a tool to do the procedure, I've got several compact Mac's I'll like to recap. 

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I was going to say this but you beat me to it.  :p

Adjusting PP1 should be your last resort! 

 

Quoting CCAdam's Classic Mac Repair Notes:

About the Macintosh Plus... (R56 is the voltage potentiometer on the Mac Plus, it is the same thing as PP1 on the Classic/Classic II) 

 

Although this voltage may be adjusted by R56, you must resist the temptation to tweak the voltage adjust trimpot for now, otherwise you run the risk of turning a minor problem into a major meltdown. Here’s why: The power supply produces several voltages simulta- neously. It actually only monitors and controls the +12V supply directly. All of the other voltages are derived indirectly from it. If there’s extra resistance in the 5V line that causes some voltage drop, that won’t show up in the +12V supply, so it doesn’t get corrected. Now, if you try to “fix” the problem by adjusting R56, you will be increasing the +12V supply voltage to compensate a 5V problem. When the 5V line is happy, the +12V line could be way over spec, causing bad things -- maybe irreversibly bad things -- to happen.

 

You should recap that Analog Board (AB). Don't worry too much about voltages. I used to, now I don't really care anymore.

Just let the mac sit comfortably, UNPLUGGED, for about a week. Flick the power switch a couple of times after shutting it down (again unplugged). This drains power and discharges those big capacitors.

 

After that, all will be fine.

You are a lucky man! Usually that battery eats away all the copper in those traces. It requires a lot of time and effort to cure.

 

Good luck  :p

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Ah yes, not intending to dish out bad advice! Definitely recap the AB. In my case, after recapping, the voltages were on the low end of spec without adjusting PP1.

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Thanks guys, that is good advice. What I usually do when I repair an Atari power supply is after the repair is complete, I load the supply with a resistor in each power rail, to avoid that the supply cuts output because there is no load. Then I adjust the 12V rail to a close value and fine adjust the 5V line. As far as I can remember this procedure always gave me a exact 5V value and a very close to 12V value (usually 11.8~11.9V).

 

Those analog boards, as they combine the power supply with the CRT electronics never work without load but the voltage values go a little crazy without anything attached. I checked that last sunday and with no logic board or floppy or hard drive, just the crt and the fan, the 5V rail bumps to 5.3V and the 12V rail falls to 9V.

 

Any of you know were I can get a logic board schematic or power&video connector pinout?

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Any of you know were I can get a logic board schematic or power&video connector pinout?

 

http://maccaps.com/MacCaps/Schematics.html

 

 

 

I checked that last sunday and with no logic board or floppy or hard drive, just the crt and the fan, the 5V rail bumps to 5.3V and the 12V rail falls to 9V.

 

If the problem is not solved with new caps, replace the optoisolator, common issue.

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Thanks to everyone.

 

Schematics:

I do not know how good or bad are that schematics, but I find $25 quite expensive cosidering I'll use that as an afficionado, and probably just once. 

 

Optoisolator:

I've found a photo here (https://68kmla.org/forums/index.php?/topic/25768-macintosh-classic-ii-analog-board-repair-help/?hl=optoisolator&do=findComment&comment=273523) and the optoisolator reads CNY75GB so CNY17G-3 is a compatible one? Has it better specs than the original? I ask because I've found that RS has both at almost the same price:

 

CNY17G-3: http://es.rs-online.com/web/p/products/7085336/

 

CNY75GB:  http://es.rs-online.com/web/p/products/7084585/

 

They look the same but the CNY75GB has a faster drop time (is it said drop? I'm reading in spanish "Tiempo de Bajada Típico"), wich I don't know if it is better or not.

 

CRT discharge:

I'm preparing to disassemble the analog board so I've buit myself a CRT discharge tool:

 

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...and I've found @ archive.org the security bulletin that explains how to discharge the tube and where to attach the tool to not damage the logic board, so now I think I'm ready to take it apart safely.

 

If anyone is interested, the discharge tool is made from PVC tubing, 1m. cable, 2 corks, one alligator clip,  and one bicycle spoke.

Edited by GroovyDrifter

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I don't know the difference. The part number I listed is what came out of my Classic. I would replace with the same part number if possible.

Concerning the Optoisolator one reference is for the Classic, the other for the Classic II, but probably one will fit the other.

 

Ahhh... ok that explains it. I can't order the capacitors until I dissasemble the board (I know the values, but I want to measure the size and the pads distance)  so I'll order the optoisolator my actual board has.

 

One question: The white plastic that covers the solder side of the Analog Board, How is it removed?

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One question: The white plastic that covers the solder side of the Analog Board, How is it removed?

 

by removing the black rivet like pins.

 

Push the center of the pin on the opposite side of the domed head (so pushing from inside out) then remove the complete unit, on reversal, push the center pin towards the domed head, and the pin will be locked into place.

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Finally I removed the board monday, instead of saturday... we had to deal at home with an issue with one vitro ceramic hob and that gone first (it burn itself). Anyway monday was holydays here so no problem at all.

 

I did found a floppy stuck inside the drive.

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The CRT was already discharged, I heard nothing when apllied the discharging tool, but having it gave me the confidence to continue. All I did was following Apple service manuals, so easy.

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I decided to clean the plastic housing, so I completely removed all the parts.

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The case after the cleaning. Part of the yellowing was dirt, but it could use a retrobright too. I choosed to not do it and keep the apple sticker attached.

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After reassembling it, except for the analog board. I cleaned all the metal parts and re-greased the floppy drive. 

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Some photos of the analog board... almost all the capacitors on the output side of the power supply are damaged, the rest look good, but will be replaced anyway. Most of the power transistors and regulators, and the optocoupler will be replaced too. The replacement parts are on their way, but they're taking longer than usual. TME has sent their parcel but RS has just sent the thermal silicon grease, none of the capacitors... :(

 

I've choosen longest life, lowest leakage current (low ESR), 105ºC capacitors, wich in almost every case leaded me to a Rubycon capacitor. And they are not cheap. Most of them are smaller than the original ones, maybe It's a good idea hot-glue some of them.

 

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The optocoupler finally was a CNY17G-3, so either the Analog board was replaced by a Classic one at some point or it was also a factory option for the Classic II

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Being a switching power supply it was quite surprising to find a linear regulator. It may be still good but I've bought a Double Gauge replacement and hight thermal conductivity silicon grease. It has two unipolar mosfets, I suppose one is for the Power Supply and the other for CRT.

 

There are two parts that I've not found new, best option I've found were new old stock in ebay: the TDA4605 and the TEA2037A. I'll keep them unchanged. Have you ever had a problem with those two parts?

 

 

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Hi!

 

This morning my last parts arrived so after work I've spent my afternoon replacing components in the analog board.

 

I first started replacing the power transistors, rectifier bridge, that big diode near the transformer, regulator and optoisolator. Well... it really gone first the big cap at the input side of the power supply, :)

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Then all these electrolytic capacitors were waitng to replace those in the board

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Hey,-ho... let's go!

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Some hours later the field was full of the dead bodies of all those capacitors that gave ther lives in the hot guts of this compact Mac. May them rest in peace(s).

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Following some views of the field of glory, with those new components that replaced their old mates waiting to hear the call of duty... or should I say the power-on chime?

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Should I add tho that a "REBUILT IN SPAIN"?

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But wait... will it work?....

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YES!

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Yatta-750x410.jpg

 

 

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