exxos's Atari, Amiga & retro forum

DoG wrote: 04 Feb 2021 19:33 Search for the power connector in schematics. Trace the POWERGOOD to the LM556. There you have HALT and RESET.

ahhh.. was looking for something "less complicated" :roll:

ok, so pin 5 and 9 are the output for the 556.

at the moment what I have easy at hand is a Multi meter, is there a worthwile test I can do there?
This is from the manual. it says pin 17 TTL high.. in this instance I assume thats 5v. but if I get the flickering 5v there.. all that shows me is what I already know issue with the reset circuit. How do I fix it?

I have tested the S201.. it works.. I get high and low on pin 8 of the 556. when pushing it.

James

Normally the 10uF caps go bad. Fitting 22uF can be better as well.

OK, found that the 12v line was shorted.

Found that C224 was shorted (from the 12v line)

I have a question though C226 and C227 frank had said should be 60ohm on mine they were about 120ohm

I tested on the other board to compare.. C224 was not shorted.. lol... but also C226 and C227 were 50ohm.

IF I have to replace anyway.. which is better? since its a cap.. I assume higher resistance is an issue? remove both the 470uf and the .1uf and test them? replace?

James

Have you taken C224 out of the MB to test if its shorted or not ?

well in the board with a OHM meter on either side I get 0.. none of the other ones are doing that. A cap should never have 0 ohms no?

James

Bikerbob wrote: 04 Feb 2021 22:08 cap.jpgwell in the board with a OHM meter on either side I get 0.. none of the other ones are doing that. A cap should never have 0 ohms no?

You are measuring the *entire* 12V rail doing that , not just the cap.. you cannot test stuff like that in circuit.. id be surprised if a 100nF cap was shorted..

I am reading the whole 12v rail measuring from one lead to the other?

OK.. I can remove it. hoping to determine the issue before I heat up the iron.

James

Bikerbob wrote: 04 Feb 2021 22:26 I am reading the whole 12v rail measuring from one lead to the other?

One side is gnd, other 12V.. so *anything* on the 12V rail is of course all connected... measure across 12V on the floppy or HDD power cables..

But 12v is grounded on the board.
Without the PSU connected to the board. So I would think I have to figure out where 12v goes on the board.

James