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 Post subject: 3400c component level repair
PostPosted: Wed Feb 09, 2005 3:09 pm 

Joined: Wed Feb 09, 2005 3:03 pm
Posts: 1
I just picked up a 3400c to tinker with. It came without a power adapter which was ordered from a 2nd party. Never having owned a Mac before I assumed the power connector was a plain RCA phono style. Anxious to see it turn on and too impatient to wait for the genuine power adapter to show up I tried applying power using a B&K precision lab supply. I set the voltage to 24, current to zero, inserted the phono plug and connected the supply. Ramping up the current to no more than one amp I saw near zero volts. I figured a polarity reversal zener diode was protecting it in forward conduction mode which meant I must have the leads reversed. Tried it the other way with the same near zero volts result but this time smoke and I heard the computer chime.

Opening up the chassis I found component DZ4 near the power connector charred and zero ohms. It had done it's job well laying down it's own life for the sake of the greater good.

So here's what I know. I know it was a zener diode of some sort. I know it probably had a reverse breakdown greater than 24v. A similar component DZ2 nearby is labeled H8. Half of the H on DZ4 is still legible but the other half is toast. Without a schematic diagram I have no way of telling for sure what the component value is or what a suitable replacement might be.

Now with the correct power supply in hand the computer will not turn on. Either something else is fried on the MB or it will not function without this diode.

* Does anyone have a full schematic they can send me in pdf? or maybe just a scan of the area in question?

* Was it just a shunt and should the computer work without it?

* If someone has a schematic that they don't want to share, can you at least tell me what the value of DZ4 was?

* Was it a standard Zener?

I'd really like to resurrect this machine if I can.

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PostPosted: Tue Jun 21, 2005 9:19 am 
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Joined: Mon Feb 24, 2003 1:58 am
Posts: 940
You're better off just replacing the whole logic board. Component level repairs are iffy at best usually, and often it is simply cheaper to replace the whole board then source specific components.


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