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MOS Kim-1 Alive!!

Moonferret

Moonferret

Experienced Member
Joined
Jun 20, 2003
Messages
489
Location
Northwest (UK)
Hi Folks!

I recently took a gamble on a spares & repair Kim-1 that was listed on Ebay. I had read that if the 6530's were dead then it would be a very pretty paperweight but I thought what the hell. I've always wanted a Kim-1 and love the simplicity of early SBCs :)

Anyway, machine arrived and yup, it was faulty. I decided to check the obvious, reset signal, bus activity, etc. Ahh, no clock signal! Wired up an external 1Mhz clock and it seemed the CPU was pulling that down. CPU replaced and I then had a clock signal but nothing on the display and the CPU stopped running after a second or so. Next step, check memory decoding was working. Nope! Replaced a 74145 and I had some signs of life. Yay! Occasionally, hitting reset would light up some of the segments on the displays. After a bit more troubleshooting (Using piggyback method) I discovered two faulty RAM chips so these were swapped out.

Yes! it's working! ... Almost! The display was coming up with a memory address and contents. I could examine and edit memory but there were a few non-working segments on the displays. I figured I was almost there so ordered a couple of replacement displays. I decided to replace all 6 to ensure even brightness. Again, almost there but not quite. The bottom segment on each of the displays wasn't working. This was traced to a faulty 7438 which was swapped. Woohoo! I now have a working Kim-1 :)

Still got a few bits to tidy up such as cleaning the board and removing the temporary socket the CPU is in but I'm really happy with the results. Here's a photo...

DSC07197.jpg

Cheers,
Dave
 
Congrats Dave!

I love it when people get an item off Ebay that is probably junked and get it up and running!
Looks like it fell into the right hands! Well done on your fault finding exploits!
 
Thanks guys! Always a sucker for a poor old machine in need of repair :)

Next step is to wire up the cassette interface and try out some programs from the 'First book of KIM'

Cheers,
Dave
 
Way Cool.... If it's the same one for $300 a month ago or so. I was thinking of getting it to. Priced far lower than all the others lately. I don't think I would have had as much luck repairing it as you and it would have ended up in a frame hanging on the wall.
 
The seller listed a pair of them with a buy-it-now price of $300 each. The 2nd one was a later Commodore version.
 
Moonferret said:
The seller listed a pair of them with a buy-it-now price of $300 each. The 2nd one was a later Commodore version.
Click to expand...

Congrats! I have a KIM-1 I've been meaning to get going myself. I know how great it feels to break through.. that's what happened when I finally got my PET 2001 to post properly after 9 years as a doorstop. Could I ask what you are using for power supply? (Model?). Keep meaning to get one for mine.
 
Moonferret said:
Hi Folks!

I recently took a gamble on a spares & repair Kim-1 that was listed on Ebay. I had read that if the 6530's were dead then it would be a very pretty paperweight but I thought what the hell. I've always wanted a Kim-1 and love the simplicity of early SBCs :)

Anyway, machine arrived and yup, it was faulty. I decided to check the obvious, reset signal, bus activity, etc. Ahh, no clock signal! Wired up an external 1Mhz clock and it seemed the CPU was pulling that down. CPU replaced and I then had a clock signal but nothing on the display and the CPU stopped running after a second or so. Next step, check memory decoding was working. Nope! Replaced a 74145 and I had some signs of life. Yay! Occasionally, hitting reset would light up some of the segments on the displays. After a bit more troubleshooting (Using piggyback method) I discovered two faulty RAM chips so these were swapped out.

Yes! it's working! ... Almost! The display was coming up with a memory address and contents. I could examine and edit memory but there were a few non-working segments on the displays. I figured I was almost there so ordered a couple of replacement displays. I decided to replace all 6 to ensure even brightness. Again, almost there but not quite. The bottom segment on each of the displays wasn't working. This was traced to a faulty 7438 which was swapped. Woohoo! I now have a working Kim-1 :)

Still got a few bits to tidy up such as cleaning the board and removing the temporary socket the CPU is in but I'm really happy with the results. Here's a photo...

View attachment 1052529

Cheers,
Dave
Click to expand...
Hey Dave,

I know you posted this a long time ago, but I could use your help. My KIM-1 just stopped working. Like you I have checked all the obvious voltages and the Clock is working and I probed pin 40 as I pressed RS, to see that pin go low. I looked at the two 74145s everything looks pretty good. So, I am guessing that there may be a problem with the zero page memory. I have a bunch of 2102s that I can use to piggy back. What method did you use to determine which ram chips were faulty?

One thing that did look a little strange to me, when testing U4 (74145) I could see strobing on Input B (AB11), but no strobing on output 2. Output 6 was strobing , which seems like that would be the 6530-003 I would expect to see activity on the 6530-002 using the K7 line.

This is what I see:

(U4) 74LS145

Input A (AB10) High
Input B (AB11) is blinking (???) Wouldn’t output 2 be blinking?
Input C (AB12) High
Input D = Low

Output 0-5 & 7 = High

Output 6 = Blinking (Shouldn’t Input C and B be blinking? ) Again, using logic probe, maybe not the best.


2102 memory

Data In = blinking fast
Data Out = blinking slow
Chip EN = High (using probe)
Address lines = blinking (After RS pressed)
R/W = blinking


When this first started happening, the display would light up after hitting RS but the address on the display would change. Until finally nothing would display. However I still see flashes on the display when I turn power off.
 
If the 2102 Chip EN is HIGH - then K0 (U4 pin 1) is not being activated - so the RAM isn't even being enabled. As a result, I don't think your problem is related to the RAM unless it results in the firmware misbehaving and getting itself into a mess (which may actually be the case)...

From the U4 input signals you have identified then the following should be true:

Code: 
D C B A
0 1 0 1 = 5 = U4 pin 6 (K5) active (CS1 on U3 6530).
0 1 1 1 = 7 = U4 pin 9 (K7) active (RS0 on U2 6530).

I assume that the 6502 CPU pin 7 (SYNC) has activity on it? If so, this indicates the CPU is still working and fetching/executing instructions.

At this point (on a PET) we would install a NOP generator and make sure that all of the outputs from U4 are operational. I assume one of these will work on a KIM-1?

Be aware that a piggyback test will only generally work if the output of the faulty RAM is not pulled to a logic 'LOW'. Hence this can be a bit hit and miss. I assume your RAMs are all soldered in rather than being in IC sockets?

Dave
 
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