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KIM-1 Repairs continue

falter

falter

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Joined
Jan 22, 2011
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Okay so I'm learning about scopes here but not still not enough to actually use one. Meanwhile, I'm doing the tried and true 'chip swap' method and just messing around with the logic probe to see what I can learn about this KIM-1 I have.

To recap, there is nothing on the display when I hit reset. There *was* a broken 556, that was replaced and we can see the reset signal all over the board including the CPU. I also checked out the 74145s and confirmed the LEDs do work (by shorting specific pins). So not that. I removed and checked the CPU in an Apple II I have -- works perfectly.

I'm wondering to what degree RAM can impact things. Would bad RAM knock out the display entirely? I've looked at the RAM with my logic probe, and every RAM chip after reset has the same pins high and low. I don't know enough to know if that tells us anything, but I would have thought there'd be some differences somewhere (?).

Anyway, I've mastered careful desoldering now so I'll just check them out quickly.. easy enough.

Obviously if one of the RRIOTs are gone I'm dead in the water. I do actually have a spare 6530-003 but not the -002 and I think that's the critical one.

Anyway, if anyone has any other suggestions pending my learning how to use a scope.. I'm all ears. And don't try to give me scope instructions just yet.. this is *way* over my head right now. :)
 
When I was repairing my first KIM, I had a similar issue. I found that piggybacking RAM chips gave me some life on the LEDs (had two faulty RAM chips). Might be worth a try here. The KIM certainly needs some good RAM to function enough to drive the display.
 
I tried piggybacking on all of them but didn't get any life at all on the display.

I wish I understood more about the flow of things. It feels like there's still possibly an IC in there holding the whole thing down. I find it odd the RAMs all have the exact same pins high and low.. would have thought there'd be some variation. I pulled a few chips and tested them in my DG.. on the first one there was a problem initially but now it's fine.
 
falter said:
Obviously if one of the RRIOTs are gone I'm dead in the water. I do actually have a spare 6530-003 but not the -002 and I think that's the critical one.
Click to expand...

Falter,
For the display to be blank, the 6530 (U2) outputs PB1 thru PB4 must be stuck high. That may indicate U2 is not working or it is not getting proper chip selects, clocks, etc. Zero in on that chip. If it turns out that the internal ROM in that chip is bad, all is not lost. A small EPROM can be used to bypass the internal ROM. If some other part of the 6530 is broken, I think a 6532 with an EPROM can be kludged to by pass the entire 6530.
 
Thanks Dave,

Yes PB1-PB4 on U2 are all stuck high. I checked the 74145 at U2 and it was fine (although the pins it connects to U2 with were all stuck high). I do have about 10 6532s in my inventory.. do you have a link anywhere on how to do an eprom?
 
Hi
The bus expansion has the ability to do full control.
I talked about making a debug board for the KIM.
It would not be to great an effort. You'd need to write a little
code for it is all.
It sounds like the buss is OK and the processor is working.
That is all you need.
Start simple by writing something to the display.
You just need to start with a connector, address decoder
a EPROM and socket.
An evening of wire wrapping or point to point.
You might add a switch to be able to enable and disable
turning off on board ROM.
You don't even need a scope. A logic probe would be fine.
Dwight
 
falter said:
Yes PB1-PB4 on U2 are all stuck high. I checked the 74145 at U2 and it was fine (although the pins it connects to U2 with were all stuck high). I do have about 10 6532s in my inventory.. do you have a link anywhere on how to do an eprom?
Click to expand...

We need to find the 1K binary image of the -02 6530 ROM and I could burn a 2716 EPROM. However while looking for the binary image, I found this info that implies a problem with the KIM-1 RRIOT chips. Check the last sentence:

Within the 8 KB-boundary the system looks like this:


K0 $0000 - $03FF 1024 bytes of RAM (8*6102)
K1 $0400 - $07FF free
K2 $0800 - $0BFF free
K3 $0C00 - $0FFF free
K4 $1000 - $13FF free
K5 $1400 - $16FF free
$1700 - $173F I/O, timer of 6530-003
$1740 - $177F I/O, timer of 6530-002
$1780 - $17BF 64 bytes RAM of 6530-003
$17C0 - $17FF 64 bytes RAM of 6530-002
K6 $1800 - $1BFF 1024 bytes ROM of 6530-003
K7 $1C00 - $1FFF 1024 bytes ROM of 6530-002


K0..K7 = output lines from 74145


Notice the way how the I/O- and RAM-areas are arranged within the area $1400-$17FF. If you study the schematics, you won't find any logic who is taking care of it; this is done inside the 6530. Even if you forget the internal ROM for a moment, it means that you cannot exchange the 6530s with each other like the 6526 CIAs in a C64.
Click to expand...

I found this on this page: http://www.6502.org/trainers/buildkim/kim.htm

I'll have to study the spec sheets to see if a 6532 can replace this "custom" 6530.
 
Moonferret said:
Another member, Osgeld provided these links in another thread for a neat little board to replace the 6530's found in PET disk drives...

http://blog.tynemouthsoftware.co.uk/2015/10/mos-6530-replacements.html
http://www.baltissen.org/newhtm/6530repl.htm

Cheers,
Dave
Click to expand...

As it is, it may or may not work. As I recall, there were several
configuration bits in the 6530 that may not match the generic 6532. It has been a while but
I think it has to do with the port mapping and such. These would be setup
by the person designing the 6530.
I believe there are ways to handle these but it many not be as simple
as this board.
Still I bookmark this page.
Anyway, I've been trying to get him to stop doing an Easter egg
hunt and do some actual trouble shooting.
It may be the 6530 that is bad. it may be something else.
To go through the trouble of making a replacement for a good part
is not trouble shooting.
I may even be a broken trace on a feed trough on the board.
I had a SYM-1 with that as a problem once. All the parts on the board
were fine.
Trouble shooting is finding the bad part, not just swapping every
thing out. Heck, why not replace the entire board!
Dwight
 
Dwight Elvey said:
Hi
The bus expansion has the ability to do full control.
I talked about making a debug board for the KIM.
It would not be to great an effort. You'd need to write a little
code for it is all.
Click to expand...

Dwight,
This is a good idea and quite similar to what has to be done to replace the boot ROM in the 6530. Typically one would ground the RS0 signal at the 6530 (U2-pin4) to disable the internal ROM, and then piggyback a 2716 EPROM to replace the suspect ROM. You are saying to do this externally with the P1 expansion connector and use diagnostic code rather than boot code. It would be up to the OP to see if his electronics skill is up to building a breadboard. I finally found a good schematic for the KIM-1 HERE thank to Ruud Baltissen.
-Dave
 
I'll try to draw up a schematic. I've looked at it and see that I'll need to
use both P1 and P2 but only a few wires on P2.
I decided to use the KIM's decoder but allow the test EPROM to remap
after reset and a small init code to one of the open areas. It isn't much
hardware and allows one to completely test the entire board.
I found the same schematic. It is hard to read the to different RD/WR signals
but I think I figured it out.
I think a 2764 is a good size to use. The KIM's decoder is 1K blocks so
I could remap into 0C00 to 0FFF after boot.
A larger EPROM could be used with a dip switch to select multiple blocks
1K is quite a bit of code space.
A 1Meg EPROM could have up to 1024 unique blocks with a simple dip
switch. Or, 512 each 2K blocks. I think I'll leave that up to the implementer.
It might depend on what programmer and EPROMs a person has.
The wiring difference it trivial.
The code to switch blocks could be as simple as a read to the new block
address ( what I intend to do ). A 7474 will work fine for the hardware
part.
If I use the KIM's decoder, I need K3 from P2.
I need DECEN from P2 anyway.
I'm going to do 1K blocks because it is simpler and less logic.

Here's a part list:
2764 1 ea
7474 1 ea
7420 1 ea
7400 1 ea
10K 1/4w 5 ea
470 ohm 1/4w 1 ea
RED LED 1ea
4 position DIP switch 1ea
14 pin socket 3 ea
28 pin socket 1 ea
0.1 uf ceramic 4 ea
Double 22 pin edge connector 2 ea
Proto board

Schematic when I get home.
Dwight
 
Just out of curiosity, I wonder if he has connected a jumper from P2-K
to ground?
If not, the onboard decoder doesn't work and it goes off
to never-never land.
I'll post the schematic later anyway. Maybe someone will pick it
up and run with it.
Using the 2764, there are 8 1k blocks of test code. I'm thinking of
using the unused half of the 7474 as another LED control
in case there is no KIM LED that we can get to light.
It is nice to know if something like the RAM test worked.
It may need another chip, though.
I think I see how to avoid that though.
Dwight
 
Dwight Elvey said:
Just out of curiosity, I wonder if he has connected a jumper from P2-K
to ground?
If not, the onboard decoder doesn't work and it goes off
to never-never land.
Click to expand...

Dwight,
Yes, I see what you mean. If that signal DECEN is left open, nothing is enabled; no display no anything. This is nuts; proper operation of the KIM-1 depends on a jumper on the USER Port? I checked the User Manual and sure enough it says in Note 2 not to forget to connect pin K to Pin 1 on the Application connector.

Falter: Check to see that DECEN is held LOW at U4-pin12. When the Application connector (P2) is hooked up for power, etc., pin K must be tied to pin 1 (ground) to enable the address decoder.
 
I'm having some issues with the schematic. The hand drawn picture
seems to be to big.
The scanner I have only does pdf and a hand drawn is about 450K.
It is about 10 time bigger than it will take as an attachment.
I've got to find a way to do a computer drawn. The drawing tool
I've used in the past has be removed by our IT.
Dwight
 
If there's interest in a premade PC board for testing your KIM-1 and no one else can/wants to lay it out, I can probably borrow a KIM-1 from a friend and do the layout. Unfortunately I had to sell my KIM-1 to help pay for unexpected college expenses a number of years ago :(
 
Thanks guys. I'll check the DECEN line again shortly. Pretty sure it was low.

And yes.. I must have checked the ground connection from pin 1 to K a dozen times. Unless I've mistaken where K is.. I'm pretty sure I have it.

Just FYI I am currently using an Amiga 1000 power supply if that makes any difference.

When this adventure first began the first clear problem I found was that the IC that handled Reset was not doing its job.. replacing that shows reset gets to the cpu. But yeah.. thats the only progress ive got. I am trying mightily to read and learn and figure out this usb scope I have but it's pretty out there for me still.
 
Hmmm..

Just decided to check resistors while I was at it. I discovered the resistor immediately below the 560ohm one beneath U4 actually is cracked.. nothing getting across. So I'll replace that and keep fingers crossed that it helps.
 
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