Need Help - Short (?) on A3000 Daugherboard

[madgrizzle]

I mentioned this in another thread regarding problems I'm having with the RTC clock on my Amiga 3000.  When I have the daughtercard plugged in, I have a short between ground and +5V when measured with a continuity tester.  With the daughtercard out of the computer, can can test the card for continuity between edge 5 and 3 and it's pretty steady. I've sat there for at least 30 seconds with continuous tone.  There are four 220uf caps on the daughtercard, but I have no idea how long it would take to charge them with my multimeter.

The board looks really clean except for one spot on the back.  It looks like someone desoldered and then resoldered the (-) lead of C601.  The (+) lead looks like the original manufactured solder.  I assume this was to measure whether or not the cap was good.  See picture.

My questions are whether or not I should see continuity between +5V and ground on the daughtercard Zorro slot edge connector for as long as I am?  If not, and someone tried to check if the cap was good or not, should I start doing the same to try to figure out why I'm getting a "short"?

[Castellen]

When I have the daughtercard plugged in, I have a short between ground and +5V when measured with a continuity tester.  With the daughtercard out of the computer, can can test the card for continuity between edge 5 and 3 and it's pretty steady. I've sat there for at least 30 seconds with continuous tone.

Are you actually measuring a short (around 1 Ohm or less), or the parallel addition of the many 220/330 Ohm termination resistors that sit between the 5V supply and ground?  I suspect the latter.  You can do the mathematics on it, but I expect you'll normally see something in the order of 10 to 15 Ohms between ground and 5V.

If you're tying to repair the RTC, look at the guide I wrote on the subject.  It's specifically for the A4000D, though in the A3000 the circuit is practically identical.

[Whaka]

I mentioned this in another thread regarding problems I'm having with the RTC clock on my Amiga 3000.  When I have the daughtercard plugged in, I have a short between ground and +5V when measured with a continuity tester.

i saw the same thing on 2 A3000 DB. there's probably no short on your.
look in resistor mode, you should found something around 10 ohms. as said Castellen

[madgrizzle]

i saw the same thing on 2 A3000 DB. there's probably no short on your.
look in resistor mode, you should found something around 10 ohms. as said Castellen

Sigh.. didn't even bother to measure it.  Yep.. 11.2 ohms.. well, that's good news then.  Back to looking for the problem.  Thanks all.

[madgrizzle]

I did the measurements on the latch and everything came up 1K instead of 10K or 2.5-3K (I assume that's just the difference between 4000 and a 3000.. 3000 uses 1K pullup resistors whereas 4000 uses 10K).  Except (!) pin 6 of the latch shows about 5M resistance rather than 1K like the other leads that connect to the ROM.  There was fair amount of battery corrosion in this area so I think the trace for that pin got corroded.  However, it appears to me that it runs under the latch and possibly goes through a via between leads 3 and 4 as the trace from that via appears to head across the motherboard to the ROM.  Can someone confirm for me that this is correct before I start soldering (I've conveniently positioned the usb microscope to not show they other "soldering" I've done) ?  

Attached is a picture of what I'm seeing.

Update:  I went ahead and put a jumper between the via and the pin and the clock works and I can update the NVRAM