• Please review our updated Terms and Rules here

Kaypro II

ChrisCwmbran said:
Why would the 8 RAM chips rust when none of the others have?

Incidentally is it a useful test to power the machine on with none of these RAM chips in situe?
Click to expand...

Well, how many other Mostek chips do you see on the board? Manufacturers have their proprietary plating processes for IC leadframes. Could have been a bad lot or just characteristic of that vendor's chips.

You can try the CPU without memory, but the results probably won't tell you anything.
 
Ok good point. The two Z80 PIO chips are made by Mostek and their pins are quite bad too.

Is http://uk.farnell.com/zilog/z84c2006peg/ic-pio-z80-6mhz-84c20-dip40/dp/1081865?CMP=KNC-GUK-FUK-GEN-KWL#relatedProducts a suitable replacement for them? I ask because these are 6mhz units....

The Z80 PIO isnt a Mostek chip however its pins are a little corroded:

IMG_20120701_174244[1].jpgIMG_20120701_174307[1].jpg

The pins do however feel strong as normal. Is there something I can do to stop these getting worse or should I just replace it anyway?

You are right though! None of the other chips in the machine are Mostek! Did they make the legs of their chips from cheese? :p
 
Last edited:
Is there anything you can do? I don't know--perhaps tin the tarnished legs with some solder, but be sure to clean up with alcohol after you're finished to get rid of any residual flux. The Chinese IC pull sellers seem to do that a lot. The danger of course, is that you'll compromise the seal between the leadframe and package,so be prepared to replace an IC if you mess up. Fortunately, Z80-family parts aren't hard to find.

That Farnell part should work fine, although, crikey, the price is pretty high! I can remember when Z80 CPUs sold for about USD$0.75 each in quantity.
 
I see far more variation in prices on the 4164s! I get the impression that perhaps Samsung still make them - some overseas suppliers seem to have tens of thousands in stock (according to the web) and charge as low as about £1 each. On ebay they seem to be on average £3 or 4 each.

Other than Ebay I havent managed to find a UK supplier who seems to have new stock other than a few odd obsolete equipment suppliers who say they have 100s in stock but don't tell you how much they are. The only other time I tried to use one of these companies I couldnt get them to respond to any emails at all.

Is the Km4164 or equivalent still actually made? I presume across the globe people are still using them in some quantities even if its not massive.

With the corroded legs do you think a little bit of Loctite 7503 might work? http://tds.loctite.com/tds5/docs/7503-EN.PDF
 
64K DRAMs were used in lots of equipment (even the later 5150 and 5160), so there are many equivalents and they should still be as plentiful as cockroaches. I doubt that Samsung still makes them, however--but the Koreans (e.g. Hyundai) made a lot of DRAM. Part numbers will vary somewhat--for instance, Hitachi uses HM4164; this reference should help.

Putting that Loctite on will likely create more problems than it solves. The last thing in the world that you should want is an insulating coating on contacts. You might try some Caig Deoxit, which serves not only as a contact cleaner, but offers a bit of protection.
 
Last edited:
Ok, I've fitted the two new Z80PIO chips, and the new RAM chips.

Decided since I was awaiting further ideas as to what to try that I'd get some info on the vertical and horizontal sync for the monitor with my scope.

Scope videos included in following posts (Sorry about this).

I've now reseated all the chips referenced on 6-6.3 (CRT Control), and all the logic gate chips (arrays?) too. Where possible, if there were a pair of identical chips I swapped them over, but no swap caused a drastic change, however now the screen has changed somewhat. I don't know if its for the better or the worse.

Latest screen shot:


I guess I'm back needed suggestions/advice?
 
Hairy!

Which accounts for 50% of why it's gone quiet.

The video section is a bog standard arrangement with counters to provide timing, a 2716 eprom to generate the characters, and 2k of ram to store the ascii text, and a quick swap of the 2114s if they're socketed might be a worthwhile thing.........

......however the way the video is flashing would seem to indicate that the CPU is just sending crap to the video section. I suspect problems with 1) ram 2) rom 3) cpu 4) decoding logic in about that order.
Not knowing the way a kaypro initialises, I don't know whether it needs ram to clear the video.

so 1) have you checked the RAM is ok?

More thoughts later
 
Here I come with stupid questions, again.

Have you verified the contents of the EPROMs? If one or more is garbage, then the CPU is just running around executing garbage, which would certainly give you that kind of display.
 
Please ask me as many questions as you want!

Personally I don't have a means to check the EPROMS. If someone is able to burn new ROMs for it, I'd gladly pay them.

Please note Chuck we sadly have an additional problem as I mentioned in a PM to Nigel - last Friday a friend who was visiting knocked the machine which was stood up on end over, and on a quick test since then the display has vanished. There's no sign of physical damage at all - but as Im sure you can guess I'm worried he may have damaged the tube. Clearly I need further information on this. I'm going to do my bench tests again to prove the PSU board with load works, and that the PSU board works with the motherboard as a load as it did before. Either way I cannot see a visible problem with the tube, and there are no visible unseated chips, or damage to the boards.
 
Tell your friend that it was working fine before he knocked it over and he owes you a new one ;-)

All the connectors solidly plugged in (especially CRT socket)? Getting power to the monitor? Filament lit?

Check those sync signals again to see if they're still there and getting to the display board.
 
You must log in or register to reply here.
Back
Top