circa77
Experienced Member
Wait a second... So you're saying you pulled and replaced those 40p DIPs and didn't socket them?
Yeah that doesn't look great, looks worse in the photo than real life, but it has continuity and is not shorting to the pins on either side...
Youthful overconfidence. Plus at the time KIM-1s weren't going for much money at all. I had one before this that I never even powered up.. sold it for a couple hundred to buy something else, then caught this one for $100. At the time they weren't fetching much money and I didn't realize how fragile they were with soldering/desoldering, nor did I have the right tools. Now they sell for $3K+. Oops. Anyway, lesson learned.My concern was that the parts for U2 and U3 had either:
1. Been inserted in the wrong position or.
2. Been inserted the wrong way around.
It is a stupid idea for the components to be ordered U1, U3 and U2 and for U2 and U3 to be physically installed the opposite way round to U1.
You can't take anything for granted, and it pays to check absolutely everything when you get a machine, or you have changed something, BEFORE applying power!
Your devices look OK though.
You need the ROMs in both U2 and U3 working, but only the RAM in U2. You should be able to get away with faulty RAM in U3 (it is available for the user to use).
The I/O ports have to work on U2 as well.
I see that the CPU is soldered in, so a NOP generator is out of the question.
Thanks for providing a photograph of the solder side of the PCB. Unfortunately, you are absolutely going to have to clean up that soldering though! It is a shame that you practiced on a KIM-1. I hope you have learnt your lesson...
I can now see what is socketed, so I will have a think. I think we can disable all of the onboard devices and force the data bus to $EA (NOP) with resistors as a test. Let me have a look at the schematics...
Why didn't you put sockets on if you changed something?
Dave
It is a stupid idea for the components to be ordered U1, U3 and U2 and for U2 and U3 to be physically installed the opposite way round to U1.
I asked because I watched some videos of using one the other day and was like.. why didn't I get one of those to start with. Ok.. ordered.>>> Would a logic analyzer help here? Would that at least tell us what 'code' the CPU is trying to run?
A resounding YES!
I just snagged an HP 1651A logic analyser from work. It was in the junk pile. It is now in the dining room awaiting test...
Dave
You're suggesting that it was someone's "idea". It wasn't. The guys who were producing those
mask parts were not the same guys as laying out the KIM PCB, and all they were doing was assigning
a suffix so they could keep straight which part had which mask, not concerning themselves with what
the component designation on the PCB might be. Totally unrelated subjects, so inappropriate to call
it "stupid", because it wasn't a thing.
Sure, but it's about 100x overkill for what you're doing. I've got a lot of test gear, includingWould a logic analyzer help here? Would that at least tell us what 'code' the CPU is trying to run?
You are correct in that the -nnn identifier is the ROM mask content. So the fact that someone decided you use U2 for the -002 part and U3 for the -003 part is inspired.
However, the concept of laying out the parts on a PCB in a non-logical ordering (when there was plenty of experience available to the contrary) was not sensible.
The same could be said for putting the U2 and U3 parts in the PCB the opposite way around to (say) U1.
So, what is your proposal then?
This has been along time since this was posted. I've not put any more debug kits together since I made 10 kits and sold them.
...
I don't know if the debug board schematic on this thread is correct ( it has been a long time).
I'm always confused about which tool is best for which job. Whenever I watch vintage computer repair videos they usually use a scope. However the few I've seen using a logic analyser look much more... er... logical to me, since you can make out the actual data. In one video the software was showing the hexidecimal opcodes and such the CPU was working on, which tells you a lot more about what the thing is actually doing. Unless I'm misunderstanding, which is likely. Why wouldn't that be a typical tool to reach for?
Thank you for that concise and understandable explanation. That really helps. Yes I was looking at some analysers online and just the physical connection of them seemed tricky, they mostly seem to come with jumper wires that have female ends.. no idea how you 'clip' those onto the relevant leads. Maybe I'd better master the scope first.The scope is almost always your number one go-to tool, because it lets you see
what's going on in real time and in the analog domain, which means you're more
like to spot something amiss - something that just doesn't look right - that's going
to lead you to the source of the problem.
Analyzers are brilliant tools, but they take a lot more setup and (obviously) won't
let you see what's going on in real time. To be more precise, an analyzer lets you
see what happened. I don't know what the youtube vids (and there are about a
million times more bad ones than good - in any field) showed you, but the way it
works is that the analyzer captures data in real time, then stops when it hits a
trigger word, or sequence, or signal, or whatever. Then you get to look back over
the recent history (depending on your acquistion memory depth, resolution, and
other settings) to figure out, cycle by cycle, what led up to the trigger event.
That can be a lot of work, and even more work if you don't have the disassembly
pod or software that turns that big bucket o' hex dump into instructions that you
can derive actual meaning from. Even just hooking up the analyzer to the target
can be a pile of work if you don't have the right pod, CPU clip/interposer. Scope:
One probe you can move around with. Analyzer: Nearly 40 connections to the
target.
So I'm not saying that you shouldn't get an analyzer - they're super to have. But
don't put it ahead of getting a decent scope.
Thank you for that concise and understandable explanation. That really helps. Yes I was looking at some analysers online and just the physical connection of them seemed tricky, they mostly seem to come with jumper wires that have female ends.. no idea how you 'clip' those onto the relevant leads. Maybe I'd better master the scope first.
Since i have a few days off, I think I'm really going to put some effort into learning how to set this scope up to be useful for what I'm doing. As mentioned it's a rigol 1102e. I wouldn't mind learning how to check some basics like seeing that the clock signal is correct, what's going on with chip enable, etc, and anything else it might tell me in this situation that might be useful. I just don't yet understand how to get it dialed in for what I want to do, or how/why to set triggers certain ways, etc.