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Kaypro II

C

ChrisCwmbran

Experienced Member
Joined
Oct 11, 2011
Messages
483
Location
Cwmbran, Wales, United Kingdom
More questions from me, re my Kaypro II this time.

The machine was completely untested so I took the top off and took a look inside. Everything is relatively clean and looked in order, so I decided to try powering it on!

The floppy drives made sounds consistent with whirring, and then two loud electrical cracking noises and a big cloud of smoke! :(

I think one flash came from the horizonal board below the back of the tube, and one from the vertically mounted board on the back of the machine.

Advice please?

How can I ensure there is no residual charge in the thing, so I can safely take the main board out to examine the two smaller boards?

Thanks again!
 
Could well be some tanalum caps going. If you're not certain, use your eyes and nose to find what went wrong. There are service manuals on Bitsavers and they're pretty good.
 
My biggest initial concern is how to make sure the circuitry in the machine doesnt have major charge in to give me a shock. I can't find consistent information on ensuring this really though, and until I'm pretty sure it has no shock surprises for me Im hesitant to proceed too far! :)
 
Stay away from the mains connections while the system is powered on. Anything else may give you a "tingle", so keep one hand in a rear trouser pocket when you're fiddling around in a powered-on unit. That makes it extremely unlikely to create a path through your body that involves your heart

If memory serves, the Kaypro has a mains input filter that uses those terrible Rifa metallized paper capacitors (look like a block of clear epoxy) that tend to go BOOM when they get old. I'd start there first.
 
Chuck(G) said:
Stay away from the mains connections while the system is powered on. Anything else may give you a "tingle", so keep one hand in a rear trouser pocket when you're fiddling around in a powered-on unit. That makes it extremely unlikely to create a path through your body that involves your heart

If memory serves, the Kaypro has a mains input filter that uses those terrible Rifa metallized paper capacitors (look like a block of clear epoxy) that tend to go BOOM when they get old. I'd start there first.
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Do I not need to worry about capacitors on the power supply or CRT etc retaining charge when the machine is off?
 
I've removed the logic board, and can see somewhat more inside the machine now.

The board that is mounted horizonally and connects directly to the CRT looks to be intact, though I thought it flashed and cracked just before the power board did (less than a second maybe).

The power supply board appears to have a capacitor that is blown apart - I'll remove the board and take photos tomorrow. Oddly on the face of it the fuse appears to still be intact!

I did notice that on the logic board the 4564N-25 RAM chips in sockets U20 thru U27, one of the two Z80s and the two 8242 chips have some corrosion on their pins. I have no idea why its only these specific chips. Tips on how to deal with this?
 
ChrisCwmbran said:
I did notice that on the logic board the 4564N-25 RAM chips in sockets U20 thru U27, one of the two Z80s and the two 8242 chips have some corrosion on their pins. I have no idea why its only these specific chips. Tips on how to deal with this?
Click to expand...

If they're in sockets, push them in to make sure they're seated. If not don't worry about it. If they're in sockets and you don't like the appearance, clean the crud off with a pencil eraser.
 
Wasn't it TI that had a big problem with metal whiskers on their pins? I think NASA was very angry with their metallurgical processes.
 
Yeah, if you have a bunch of those old TI sockets, save them for your $10K Apple I replica... :)

I hated TI sockets. When I discovered Augat machine-pin sockets, I quit looking...
 
The power supply board is an Astec AA12350. The capacitor that blew is C2, and C1 and C13 are possibly questionable in my view:

IMG_20120607_113908.jpgIMG_20120607_113938.jpgIMG_20120607_114018.jpgIMG_20120607_114049.jpg

Unfortunately C2 is so shattered I dont know what value and type it is at all. Anyone know?

Do people agree it looks like C1 and maybe C13 are also gone?

Clearly they are 0.01uF capacitors, but what is the full description of the three parts I need to order?

Also, are they of the same values as I'll find in my other stuff such as BBC Micros, and accordingly should I order a number of each?
 
As far as I can see, C1 and C13 are "Capacitor X2 10nF 275V 18x5x11mm" according to RS Components here.

From what I can glean it appears C2 was almost certainly "Capacitor X2 100nF 275V 18x6x12mm" and is just a larger size from the same range.

I hope Im right - I ordered some of each :)
 
That's what the schematic says. The hated Rifa caps as I noted before.

Oddly enough, these are sometimes referred to as "safety" capacitors--not for not exploding, but failing in a predictable way so as not to endanger the user if they fail.

But we've been here before, I believe.
 
ChrisCwmbran said:
Do you mean can we remove the need for them? I dunno! Chuck is much more of an expert than me!
Click to expand...
Assuming nothing else is wrong, the computer should work just fine without them.

Right I have received my bags of new capacitors. How do I tell the polarity of these? It doesnt appear to be marked!
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They're connected across alternating current, so they're non-polarized; I assume they are type X2 ?
 
MikeS said:
They're connected across alternating current, so they're non-polarized; I assume they are type X2 ?
Click to expand...

Yes they are! Thanks for that info! Maybe today will see my Kaypro return to operational state! Fingers crossed!

If anyone wants to see the pics of the blown up capacitor they are on my website in the blog.
 
Right I've reassembled the machine having replaced the 3 capacitors.

When it's turned on now I hear what sounds like a whirring noise but I think it's electrical.

I disconnected the power connector from the logic board and the values read are as follows:

-12 is reading -3.51v
+12 is reading 0.03v
+5 is reading 0.18v

Ideas please?

I thought the chirping was coming from the CRT but having unplugged the video card I'm now pretty sure its coming from the PSU.
 
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Well, at least things aren't blowing up on you. I think the Astec supply will operate without a load. Have you tested it with nothing plugged into it?

We need to figure out what part of your system is the problem.
 
Testing the PSU on its own not connected to anything its still chirping.

The -12v pin is stable at -12.5v .

The +12v is varying constantly between about 7v and 12v by the look of it.

Similarly the +5v is varying between 3.8v and 5v or so. Its obviously hard to say because the display of the meter only updates at a certain speed.
 
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