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Author Topic: Need Help - Short (?) on A3000 Daugherboard  (Read 1120 times)

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Offline madgrizzleTopic starter

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Need Help - Short (?) on A3000 Daugherboard
« on: December 03, 2017, 01:30:07 PM »
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"?
Only Amiga *woo-woo* Makes It Possible
Only Amiga   ... Makes.. It .. Happen!
Amiga 2000, 2MB Chip RAM, OS3.9, GVP Combo 030/22 13 MB, Supra 4MB
Amiga 3000, 16 MB RAM, OS3.9, A3640 v3.2 with 060 Processor, Picasso II, A2065, PCD-50B
Dead VA2000/CX :(
 

Offline madgrizzleTopic starter

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Re: Need Help - Short (?) on A3000 Daugherboard
« Reply #1 on: December 04, 2017, 01:24:09 AM »
Quote from: Whaka;833760
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.
Only Amiga *woo-woo* Makes It Possible
Only Amiga   ... Makes.. It .. Happen!
Amiga 2000, 2MB Chip RAM, OS3.9, GVP Combo 030/22 13 MB, Supra 4MB
Amiga 3000, 16 MB RAM, OS3.9, A3640 v3.2 with 060 Processor, Picasso II, A2065, PCD-50B
Dead VA2000/CX :(
 

Offline madgrizzleTopic starter

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Re: Need Help - Short (?) on A3000 Daugherboard
« Reply #2 on: December 05, 2017, 02:56:59 AM »
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
« Last Edit: December 06, 2017, 03:05:04 AM by madgrizzle »
Only Amiga *woo-woo* Makes It Possible
Only Amiga   ... Makes.. It .. Happen!
Amiga 2000, 2MB Chip RAM, OS3.9, GVP Combo 030/22 13 MB, Supra 4MB
Amiga 3000, 16 MB RAM, OS3.9, A3640 v3.2 with 060 Processor, Picasso II, A2065, PCD-50B
Dead VA2000/CX :(