Array resistors: to identify them

[Eamoe]

Hi folks,

meant to post on EAB but it looks it's been down since yesterday.

I have a small A500 RAM expansion that doesn't work and I have a guess that this comes from resistor arrays on the tiny card. They look rusty/gooey right down where they attach to the board. There are 3 of them, one 10-pin and two 8-pin. They are molded in black plastic.

But how can you tell the values for these? They only bear the mention "B 101J", same for all 3...

Anyone knows about these?

 

[Allen1]

According to what I can see on this data sheet its a 100 ohm version.
http://www.bitechnologies.com/pdfs/cr.pdf

 

[Eamoe]

Thanks Allen1,


yeah, just found out that "101" actually is

• 1 for the first digit
• 0 for the second digit
• 1 for adding one zero to that number

which makes 100 Ohm indeed. Now this won't tell me if these are

common lead:

or isolated resistors:

Any clue?

 

[rkauer]

Most of the times they are the common lead variant. You can check with a multitester on 200 Ohm scale.

But green stuff is from a leaked battery, so immersing the entire board in lemon juice (squeezed fruit, seriously!) for a couple of hours will sack the goo off the board.

Wash in tap water with an old toothbrush after the treatment and pour some IPA (iso alcohol) to expel the water, let it dry overnight and test the board again.

 

[Eamoe]

Hey there rkauer, thanks, I like your style..."Just throw the damn thing into the tub and flood the whole *@?$!"

Will definitely try it and report.

 

[rkauer]

Lol, believe it or not, lemon juice is a mild acid and will start attacking lead and copper oxides and hydroxides, which are the result of battery leakage.

You can use spirit vinegar, too (diluted acetic acid) with the same effect. But citric acid (main component of lemon juice) is more secure and will not attack bare metal (the copper on the tracks and lead of the solder joints) much.