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Need help with restoring a Kaypro 2´83

Hi Elvi,

Changing old sockets can actually quite difficult. It's really easy to lift tracks up (and break them) when you try to take the old socket out...especially when the tracks are on both sides of the board. I'm not sure that's the case on the Kaypro.

This is why I suggested leaving the socket in and just jumpering the faulty cell to where is should go (although reflowing the solder on the base is always a good idea too...but doesn't always solve the problem in the socket cell itself is damaged).

However, If you are not used to soldering my advice would be not to do any right now. Particularly with a soldering iron of that wattage. You are likely to damage the board. Something between 15 and 30 watts is what you need for an electronics soldering iron.

Elvi, I'm not sure how familiar you are with electronics. Do you not have a circuit diagram for the Kaypro and if so, can you read it? Are you familar with how a multimeter works? If you are not sure, I would leave this project and learn some of those principles first perhaps by doing a simple kit or so. Certainly I wouldn't go near my Kaypro with a 60 Watt iron. I think my own soldering iron is about 25 watts.

Tez
 
i havn't changed the socket yet but what done is done now, and it's not like i hold that iron there for long, maybe 2 secs at most just to add more solder, anyway from the diagram at bitsavers, i tested the legs of u49 and everyone of them gives a litle ohm reading to both the cpu and the eprom, did the same test on the working kaypro and got the same ohm readings, between 2 and 5 ohms so i guess there is contact on the legs, did it with the chip in place btw.

i'm somewhat familiar with electronics as i learned household power in a school and got a nice multimeter from there with alot of settings, i know household power and electronic power ain't the same thing but they are related.

hers what the underside of the board looks like when i've been at it, hope it isn't too bad
board.jpg

and my multimeter and solder iron just to show you what i got.
meter.jpgiron.jpg
 
Elvi said:
i tested the legs of u49 and everyone of them gives a litle ohm reading to both the cpu and the eprom, did the same test on the working kaypro and got the same ohm readings, between 2 and 5 ohms so i guess there is contact on the legs
Click to expand...

Not necessarily. It depends which way the circuit is going to get to the CPU. It could be going through the IC and out another leg to get there.

Use a circuit diagram to see exactly where the track from each socket goes. Follow the track from the bottom of the socket to a convenient place to put a probe but before the track goes into any other component. Put one proble of the multimeter on this point and the other on the top of the chip leg. This should show a direct connection with etremely low Ohms.

You could still get a low reading if the circuitry somehow loops back through another part of the chip to that connection point so it's not necessarily definitive. One thing is for sure though. If it shows NO connection between the two probe points then you have found a faulty socket cell.

Tez
 
there is hardly any place like that at all, very few of the legs have any extra points and most goes to the next chip.

btw what did you think about the solder, was it badly done, i just gotta know :nervous:

oh and i don't understand the diagram at all with leg 19 on u49 and also i can't find u48 anywhere on the diagrams so i can't even test it right.
 
The solder points don't look too bad. I still wouldn't risk a 60W iron though. You can heat up the board too fast and damage it.

Ok, as you have the board out of the computer anyway, with the chip inserted, just measure any resistance from the top of the chip leg to the corresponding solder point on the bottom of the board. This will see if there are any open connections due to a faulty socket cell.

Elvi, I've got to get off these boards now. Maybe someone else would like to comment.

Good luck with it.

Tez
 
all the legs from the top of the chip to the bottom of the board gives some resistance like 1 or so, seems my multimeter is a litle finiky but atleast it shows something.

i tried the other kaypros u49 chip again in this kaypro and hello!? it works, thats just weird even after i've chilled the chip with an ice cube in a plastic bag it still works... i'm starting to think that the cullprint is the u49 chip itself :( it works perfectly when it's warm but when it's cold the garbled screen appears.
 
Nah nothing to report, i think the chip is screwie or something.

I pretty much gave up after the last test and screwed it together and put it away.
 
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