Help identify iMac G3 PSU Board Components

[MacMan-1984]

There are some components on my iMac G3's power supply board that are so corroded as to be unidentifiable. I am hoping someone with a matching intact PSU can post some pics of theirs.

The specific PSU board I have is LG P/N 6870T194A20. The Apple part number is 820-1143, and the Apple EEE code is MMM. There are 4 resistors I can't identify: R981, R982, R994, and R995.

In case you are wondering: no, it does not power on. It sounds like the CRT is getting high voltage, but I confirmed the logic board is not getting appropriate voltage. Then I discovered this mess and a lot of rust on metal parts of the deflection yoke, which sits right above this spot on the board.

This machine came out of a dank basement. It appears there were many times when enough humidity condensed on the metal parts of the deflection yoke that it dripped, carrying dissolved rust down with it. Hope I can revive it!

 

[MacMan-1984]

Good news! I was able to get a pic from someone in another forum. I will upload it here in case anyone else needs it.

 

[Flyinace2000]

Get your working? I've got a dead iMac with the same board. Does your measure 12v anywhere when not powered on? I get 5v and 75v at places, but no 12v.

 

[MacMan-1984]

Good news! I was able to get a pic from someone in another forum. I will upload it here in case anyone else needs it.

I used Digi-Key's 4-band resistor color code calculator to identify replacements. Here's what I will get:

• R981: 150 ohm, 5% tolerance
• R982: 820 ohm, 5% tolerance
• R994: 1k ohm, 5% tolerance
• R995: 1k ohm, 5% tolerance

The color in the photo is good and I think I got it right, but of course I'd appreciate anyone correcting me!

 

[MacMan-1984]

Get your working? I've got a dead iMac with the same board. Does your measure 12v anywhere when not powered on? I get 5v and 75v at places, but no 12v.

Not yet! I just removed the damaged resistors and identified replacements. Tomorrow I will see if I have what I need around the shop and order parts if I do not.

Before disassembly I did take a couple voltage measurements at the test points on the logic board following the Service Source manual procedure. I was getting correct +5V trickle power at J9, pin 1. However, I was not getting Down Converter On (DCO) voltage of -1.2V at C10. I do not remember for sure, but at that point I do not think I bothered to test the down converter connector for +12V. I do not think I saw 75V anywhere.

 

[Flyinace2000]

Not yet! I just removed the damaged resistors and identified replacements. Tomorrow I will see if I have what I need around the shop and order parts if I do not.

Before disassembly I did take a couple voltage measurements at the test points on the logic board following the Service Source manual procedure. I was getting correct +5V trickle power at J9, pin 1. However, I was not getting Down Converter On (DCO) voltage of -1.2V at C10. I do not remember for sure, but at that point I do not think I bothered to test the down converter connector for +12V. I do not think I saw 75V anywhere.

Ended up ordering a new old stock PSU with the same issue. I don't see any resistors that have popped, so I'm gonna order new caps for the PSU and the analog board. Lets keep each other updated.

 

[MacMan-1984]

Ended up ordering a new old stock PSU with the same issue. I don't see any resistors that have popped, so I'm gonna order new caps for the PSU and the analog board. Lets keep each other updated.

Man, it sucks that the new old stock board is like that! I have been tempted to buy one, but your story makes me hesitant.

Bad news about my board. I replaced the destroyed resistors and the traces around them are still intact. Unfortunately, still no power. I have done a bunch of probing and mapping, but I still do not think I have found anything that explains the problem.