Help identifying burnt resistor on Classic II analog board.

Genjoke

Tinkerer
Oct 31, 2021
70
42
18
Brazil - Rio de Janeiro - Flamengo
Hi folks.

I am still trying to bring a Mac Classic II back to life. Now I'm working on the analog board.

I found a serious cap leakage "scar" on the poor thing.

IMG_0464 copy.jpg


I cleaned it the maximum I could, with IPA and a lot of the green soldering mask around the affected area peeled off.

I turned my attention to recapping it.

During the process, I found a burnt resistor on position RP9 (my board is a 630-0525).

IMG_0466 copy.jpg


Can any of you guys tell me the specifications of that resistor? I tried the board schemes, but the electronic lingo is greek to me!
 
Last edited:

Cam

New Tinkerer
Dec 12, 2022
21
10
3
This one? 610 kΩ ±2% ?
(pic from the internet)
 

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  • RP9.jpg
    RP9.jpg
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Genjoke

Tinkerer
Oct 31, 2021
70
42
18
Brazil - Rio de Janeiro - Flamengo
This one? 610 kΩ ±2% ?
(pic from the internet)
Exactly that position. I can't recognize a resistor by its stripes.

Is that image from a 110V analog board? I ask that because there's also 220V versions.

I have another board here, but it's a different revision. Looking at the same spot there's an extra resistor there...

IMG_0467 copy.jpg
 
Last edited:

Swayne2k

New Tinkerer
Aug 9, 2022
1
1
3
Hello.
According to the Bomarc schematics, there are two revisions of the board: the 'early' (Samsung one) and 'late' (Hitachi). Most probably the board that has the burnt resistor is the late one. So according to the Bomarc schematics and the photo from the Internet, RP9 resistor should be 243 Ohms with 1% tolerance. I have one of these boards at home, so I can measure the exact value later in the evening.
This resistor should set the output voltage from IP2 (LM317), which should be +30.7 Volts.
 
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