Kaypro keyboard fault

[tezza]

Hi Tez
I'm not familiar with the KayPro keyboard structure but I'll try to describe
what the general serial keyboard does.
First, I'm not too surprised that you don't see any data bus changes
while holding a key. ....

Dwight

Ok,. thanks Dwight. This answered my question just posed above.

Terry

 

[tezza]

This is now getting very tricky and I'm not sure where to go next. The clock is working and the data lines seem to be working (although I would not know if they are working correctly or not).

I think I'll try the desparate measure of reseating all ICs.

Mike, I'm getting that deja vu feeling. Mike will know that I had had the scope out and active trying to fix a problem in my NEC 8201a a few weeks ago when it suddenly refused to boot. The problem was discussed on the M100 mailing list, not here. I spend a lot of time looking at the basics there (CE, Data Lines, RAM access etc...etc..). In the end, I couldn't solve the problem but someone else who took a look at the board did. It was a blown 245 buffer on the address bus. I didn't feel too bad though because it was also a major challenge for the person who fixed it. He was a hardware guru who had lots of experience with the type of machine and had all the gear. He said it was a very difficult problem to track down.

Hopefully this is not going to be the same, but it's shaping up to be!

Tez

Terry

 

[dave_m]

Tez,
Dwight's explaination clearly shows why a logic analyzer is the exact right tool for this type of computer problem, but a dual channel scope will do the trick if you are patient. Can you borrow another probe from Philip? I like Tektronix scope probes, but a probe from China is not too expensive and seem to work fine. (you see how I'm always spending your money ).

 

[pavery]

Tez,
Can you borrow another probe from Philip?

Yes, he can - I have another probe here. Geez - I didn't realise you didn't have both probes, Tez, otherwise you could have collected that yesterday too. Shall I post it over?

Philip

 

[tezza]

Yes, he can - I have another probe here. Geez - I didn't realise you didn't have both probes, Tez, otherwise you could have collected that yesterday too. Shall I post it over?

Philip

Hi Philip.

Yea, why not. I'm in so deep into the problem already....

I may need some help in interpretation once it's all wired up but if folks think it might reveal something, why not go the whole hog!

Thanks!

Tez

 

[dave_m]

Tez,
It would help to have a 40 pin DIP clip which is spring loaded and fits over a 40 pin chip and allows access to all pins of the SIO. However if you have a 16 pin clip like the attached photo, you can clip it to the source of the /CE signal which is hopefully a 16 pin address decoder chip. Make sure you clip it on when power is off to avoid inadvertent shorts, and make sure it is seated properly with no bottom contacts of the clip touching two adjacent pins on the chip.

Is there a schematic of the Kaypro available on the web so we can all look over your shoulder and join in on the fun?

View attachment 2950

 

[dave_m]

I think I'll try the desparate measure of reseating all ICs.

This should only take a few minutes. You do not have to remove the chips. In fact it is best not too, as you might bend a lead. Just rock them in their sockets by pushing down on alternate ends of the DIP.

 

[tezza]

Tez,
It would help to have a 40 pin DIP clip which is spring loaded and fits over a 40 pin chip and allows access to all pins of the SIO. However if you have a 16 pin clip like the attached photo, you can clip it to the source of the /CE signal which is hopefully a 16 pin address decoder chip. Make sure you clip it on when power is off to avoid inadvertent shorts, and make sure it is seated properly with no bottom contacts of the clip touching two adjacent pins on the chip.

I don't have any of these devices but they sure look useful. I'm not sure if my electronics shop has any of these....I was going to enlist the aid of my daughter as a second pair of hands if needs be..

Is there a schematic of the Kaypro available on the web so we can all look over your shoulder and join in on the fun?

Sure thing. There are a couple of Kaypro tech manuals on the web with schematics. They deal with all models. I've put together a subset PDF containing the Kaypro II info and schematics out of the best of these. I've uploaded it at
http://www.classic-computers.org.nz/temp/kaypro-II-schematics.pdf

The more looking over my shoulder the merrier. Just don't laugh

I only wish I could find a schematic for the keyboard. The most detailed info I've found on the web regarding the keyboard is in this document here.
http://www.slor.net/kaypro/res/Dists/kayinfo/keybrd.doc

Tonight I'll try reseating all ICs and in the event that that doesn't work, I'll summarize what's known so far. I appreciate the time and input from everyone so far.

Tez

 

[dave_m]

Another thing to look at would be the input from U78 (8116 baud rate generator) to pin 27 of the SIO. If I'm reading the schematic right, you should have a regular signal there.

cosam,
You may be right as replacing the SIO did not help. And yet most everything else must be working to have a nice display with blinking cursor and active bus data, and he sees serial input data at the SIO (although not yet proven to be valid 300 baud data).

One thing that would explain everything is a missing or incorrect baud rate clock to the SIO. That would not allow the SIO to process the serial data.

Tez: please probe the RxTxCB pin (27) on the SIO (U70). I guessing it should probably be about a 4800 Hz square wave. That is 16X the 300 baud clock. It would have a period of about 0.2 milliseconds so set the time base of the scope to around 2 milliseconds and you should see about 10 clocks on the screen. If it is OK then we may have to take a closer look at the incoming serial data from the keyboard. If it is not OK, then check pins 1 and 18 (crystal inputs) for a 5 MHz sine wave of probably small amplitude.

 

[tezza]

Getting somewhere?

Getting somewhere?

cosam,
You may be right as replacing the SIO did not help. And yet most everything else must be working to have a nice display with blinking cursor and active bus data, and he sees serial input data at the SIO (although not yet proven to be valid 300 baud data).

One thing that would explain everything is a missing or incorrect baud rate clock to the SIO. That would not allow the SIO to process the serial data.

Tez: please probe the RxTxCB pin (27) on the SIO (U70). I guessing it should probably be about a 4800 Hz square wave. That is 16X the 300 baud clock. It would have a period of about 0.2 milliseconds so set the time base of the scope to around 2 milliseconds and you should see about 10 clocks on the screen. If it is OK then we may have to take a closer look at the incoming serial data from the keyboard. If it is not OK, then check pins 1 and 18 (crystal inputs) for a 5 MHz sine wave of probably small amplitude.

I think we are getting somewhere. Before I logged in tonight and read your post Dave, Philip Avery rang me with a hypothesis. Today he'd been thinking on the problem and came to a similar conclusion to you...i.e. that baud generation might be the issue in particular the 8116 baud generator IC (or something upstream from that) that feeds onto pin 27 of the SIO.

This pin shows abosolutely nothing. Zero volts. Steve (Cosam) did hint about looking at this area earlier and in fact I mentioned earlier today that this pin was showing nothing (Quote: "There are some lines callled RxCA, TxCA and RxCxTB ...these show 0v whether a key is held down or not.")

With Philip on the phone I tested pin 17 of the 8116 (pin 27 of the SIO) and sure enough...nothing. 0v. no wave of any description. TxCA (pin 3 of the 8116 and pin 14 of the SIO) is the same. zero volts.

As we discussed (and you mentioned Dave) this would explain all the symptoms. I booted the machine with the 8116 removed and nothing changed. Boot was ok, blinking cursor but no keyboard input.

Is it the 8116 though or something upstream? I tested the 74LS14 inverters at U73 and they seem to be inverting as they should. Tomorrow I'm going to buy a logic probe from the electronics store here, to test if there is a pulse into the 8116 through this inverter IC on boot up. As I understand it, that is needed to start the 8116.

I don't have a 8116 lying around so I can't swap it out.

Also. I tried the Xtal SIO pins as you suggested. Pin 1 gives an usual (messey) display I can't really make sense of. There are strange irregular variable square waves the largest about 1us in width. Pin 17 is a steady 5 volts.

Tez

 

[MikeS]

This pin shows abosolutely nothing. Zero volts. Steve (Cosam) did hint about looking at this area earlier and in fact I mentioned earlier today that this pin was showing nothing (Quote: "There are some lines callled RxCA, TxCA and RxCxTB ...these show 0v whether a key is held down or not.")

Also. I tried the Xtal SIO pins as you suggested. Pin 1 gives an usual (messey) display I can't really make sense of. There are strange irregular variable square waves the largest about 1us in width. Pin 17 is a steady 5 volts.

Tez

Oops; how did I miss that... Somehow I thought you were talking about RxDA and TxDA...

Yeah, that's not good; you need some pulses there.

Check pin 10; if the oscillator's running then I think you should have pulses there regardless of what U73 is doing, as long as pins 8 and 12 are both low. If no pulses try gently wiggling or tapping the crystal.

Sounds like we are indeed finally getting somewhere.

 

[cosam]

Is it the 8116 though or something upstream? I tested the 74LS14 inverters at U73 and they seem to be inverting as they should. Tomorrow I'm going to buy a logic probe from the electronics store here, to test if there is a pulse into the 8116 through this inverter IC on boot up. As I understand it, that is needed to start the 8116.

Yep, the pulse is what sets the baud rate. You may be able to use a trigger on the scope to detect that pulse too, but a logic probe is definitely worth having anyway. If there's no pulse, check U57 (or replace it - they're common parts and can be tricky to test properly in-circuit). Other than that there's only U62 and U80 between there and the CPU.

Also. I tried the Xtal SIO pins as you suggested. Pin 1 gives an usual (messey) display I can't really make sense of. There are strange irregular variable square waves the largest about 1us in width. Pin 17 is a steady 5 volts.

I take it you mean pin 18 as opposed to 17, i.e. the other leg of the crystal. I'd have thought you'd have gotten a clean sine wave somewhere around there, but I could be wrong. I can see where Mike's coming from with wiggling the crystal - a bad connection here would really mess things up.

Check pin 10; if the oscillator's running then I think you should have pulses there regardless of what U73 is doing, as long as pins 8 and 12 are both low.

Definitely worth doing but I wouldn't dismiss the chip if there's nothing there. On some 8116s pin 10 is N/C, so you'd need the datasheet of your specific chip to be sure.

 

[dave_m]

Xtal

Xtal

Tez,
In case it turns out to be the 5.068 MHz crystal, can you take note of any markings on it and measure the length, width and height. Also if possible try to determine the spacing between pins (pitch).

Baud rate crystals should be common and therefore normally affordable, however this part is an obsolete through-hole package so it may be getting rare.

All of us may be going through our inventory of old modem boards to see if we can come up with a match.
-Dave

 

[tezza]

Hi Guys,

Yes, one of the first things I did was to replace U57 as it was easy to do. No effect so I assume the one there is ok. I checked the pins just in case and they seem to be giving sensible readings.

Just clarification on the crystal. I've identified the component. Is this crystal just for setting the baud rate, or is it also THE crystal that used to maintain the CPU clock? I'm assuming it's the former but I just want to make sure I'm not mistaken in that belief. Sorry if that seems a real newbie question. The clock certainly seems to be working ok.

Parts may be a problem. The baud rate generator IC has the following markings...

WD8116M-00
WD1943M-00
8250

I googled this part and it seems to be listed on some sites but there is not a lot of info on it. Much more common is AY-5-8116 or COM8116? I'd assume these are swappable but from what Steve says ("On some 8116s pin 10 is N/C, so you'd need the datasheet of your specific chip to be sure".) this might not be the case?

Yes, I decided if my vintage machines were going to break down everytime I used them(!!), I would need to bite the bullet and fork out for a logic probe.

Tez

 

[pavery]

Tomorrow I'm going to buy a logic probe from the electronics store here, to test if there is a pulse into the 8116 through this inverter IC on boot up. As I understand it, that is needed to start the 8116.

I don't have a 8116 lying around so I can't swap it out. Tez

Yes Tez. I believe the probe placed on Pin 12 of 8116 with MEM function should record the rising of the single pulse I'd expect on boot up.

How's this for a method to verify the 8116 - assuming the xtal is fine and all connections to the 8116 are fine - plus the fact that another 8116 isn't around for a swap. Try manually pulsing STBT on the 8116. Do this by grounding momentarily pin 3 of U73 to simulate /BAUDB pulse. Alternatively pulse pin 12 of 8116 from somewhere on the board thru a pull-up resistor to 5V. A working 8116 should start showing waveform of *some* frequency at output Pin 17 (probably won't be the correct frequency as it depends on what was on the data bus at the time which determines frequency.)

Do others concur with those two thoughts?

Philip

 

[MikeS]

If there really is no activity on pins 10, 3 and/or 17 then that's an excellent idea. Also, what is the normal state of pin 12 (and 8 just for fun) - are they in fact both low?

But I'd think that even if the baud rate is never strobed you'd still have activity on the frequency outputs; it's starting to look more and more like a bad crystal or 8116 or a connection.

 

[pavery]

Testing Kaypro keyboard

Testing Kaypro keyboard

If it is indeed standard 300bd serial at TTL levels I wonder what Andrew and Philip would think of connecting the keyboard to something like a Tandy M100 to see if it's outputting data?

While at this point Tezza's keyboard appears fine, this does raise the possibility of easily verifying the keyboard, now or some time in the future.

MikeS: I direct this to you, because I know you've connected more things to the Tandy Model 100's RS-232 than I can shake a stick at! Should the following work?: Leave the keyboard connected to the Kaypro, so the keyboard retains its power supply (assumed to be 5V). Connect Pin 2 of the Kaypro's keyboard socket (output signal from keyboard) and connect to Pin 3 (RxD) of the M100. Plus connect grounds. Enter TELCOM on M100 & adjust settings. With a bit of luck, keys depressed should appear on M100.

Philip

 

[MikeS]

While at this point Tezza's keyboard appears fine, this does raise the possibility of easily verifying the keyboard, now or some time in the future.

MikeS: I direct this to you, because I know you've connected more things to the Tandy Model 100's RS-232 than I can shake a stick at! Should the following work?: Leave the keyboard connected to the Kaypro, so the keyboard retains its power supply (assumed to be 5V). Connect Pin 2 of the Kaypro's keyboard socket (output signal from keyboard) and connect to Pin 3 (RxD) of the M100. Plus connect grounds. Enter TELCOM on M100 & adjust settings. With a bit of luck, keys depressed should appear on M100.

Philip

Heh. See my post # 31 ;-)

 

[pavery]

Heh. See my post # 31 ;-)

I did - that's why I quoted it in my Post #57. What I want to know now is: do you think the method I explained in Post #57, will work? (Tez has a Model 100, you see).

Philip

 

[dave_m]

Just clarification on the crystal. I've identified the component. Is this crystal just for setting the baud rate, or is it also THE crystal that used to maintain the CPU clock? I'm assuming it's the former

You are correct. The crystal Y3 is only for the SIO baud rates.