Kaypro Keyboard Konundrum

[pavery]

Greetings all

Those following Tezza's Kaypro keyboard fault may remember

On a coincidental note, a nice looking Kaypro II has just appeared on our Trade Me site. First one I’ve seen in my three years of looking.

Well, that machine is now mine. I have only a small collection - TRS-80 Model III & a few TRS-80 Model 100's. However I want to pursue an interest with CP/M and a Kaypro should do this nicely.

Buying it was quick - getting it going however is taking time. I will do a blog soon covering the issues so far fixed - yes, I have robbed you guys of some fun. However, this is the short version:

Essentially the 4164 RAM ics had very rusty pins, yet all the other ics looked great. On pulling from their sockets, many left their pins behind! These were all Mostek manufactured, around 8247 - were there quality issues for them around that time? Tezza came to the resue and loaned a full round of 4164s. Also the SIO (again Mostek) came apart - replaced that.

The thing still wouldn't boot - drives checked out, so went probing around the FDC & found the Data Separator dead. Renewed that - still no go. Then discovered the old Data Separator had corrupted tracks 0 & 1 of boot disk! Using my last boot disk with the new Data Separator - it booted! :D

Now, this next issue I am seeking advice: Keyboard Konundrum

The keyboard is in auto-repeat all the time. I've traced the fault to a port on the 8049 - pin 33 is stuck low. This port looks at a bunch of keys, but the keys are fine - there appears to be a fault within the 8049 as this pin is lo even when disconnected from the keyboard line. The port is internally pulled up to 5V - refer to 8049 datasheet. I thought maybe the internal pull-up wasn't working, so I tried adding an external pull-up - thru a 61k resistor to 5V - no change - still reads low (0.1V and heads down towards zero on my DVM).

Is there any other trick I can do to keep this port Hi, when no keys are pressed? Or am destined to find a replacement 8049 - not easy and there appears to be two different types. Tezza's 8049 is different to mine, his early Kaypro II serial-numbered machine has external ROM in the keyboard.

Thanks
Philip

 

[Chuck(G)]

I don't think there's a difference between the 8049s that you and Tezza have, other than that his pin 7 is strapped high and yours is strapped low. When high, this forces external memory to be used for program fetches. So, you can use an 8049 strapped this way to take the place of an 8039 (which has no ROM).

 

[pavery]

I don't think there's a difference between the 8049s that you and Tezza have, other than that his pin 7 is strapped high and yours is strapped low. When high, this forces external memory to be used for program fetches. So, you can use an 8049 strapped this way to take the place of an 8039 (which has no ROM).

Hmm, I'm confused by this Chuck(G). I'm assuming the early type keyboard (with external ROM (I think it's ROM, not RAM)) has an 8049 with no code stored within - hence the external ROM. Whereas the later keyboard has code within the 8049, no external ROM. So I can't see an early version 8049 work in a later keyboard. Though I can see that a later version 8049 work in an earlier keyboard.

Am I correct that with a later keyboard, I must use a later version 8049?

Philip

 

[Chuck(G)]

All 8049s have ROM. The ROM-less version is the 8039. I suspect that Kaypro probably used the 8049 where an 8039 was originally called for. You can jumper an 8049 to look like an 8039. Similarly, the 8749 is an 8049, but with built-in EPROM (it has a quartz window for erasing).

 

[MikeS]

Expanding your horizons beyond Radio Shack and large Diesel engines, eh?

I'm afraid I'm confused too about what Chuck's trying to tell us...
Sounds like you might be able to replace Tez's 8049 with an 8039, or replace yours with an 8749 if you could find one and knew what was in your 8049, but that sounds kinda iffy.

Have you tried swapping with Tez's just in case?

Sure sounds like the pull-down or input buffer is shorted to ground; probably doesn't make any difference but is it being used as input or output?

 

[Chuck(G)]

All I'm trying to say, Mike is that there is no ROM-less 8049. The ROM-less chip (otherwise identical to the 8049) is an 8039.

However...

It's possible to force the the 8049 to ignore its internal ROM and look for all respects like an 8039. Just raise the EA pin and all address references will be satisfied from external memory. My guess is that's what they're doing on Tezz's Kaypro.

Using an 8049 in this manner is also a way to re-use old, out-of-date 8049's that have already been programmed (rather than scrap them completely).

 

[pavery]

Expanding your horizons beyond Radio Shack and large Diesel engines, eh?

I'm afraid I'm confused too about what Chuck's trying to tell us... Have you tried swapping with Tez's just in case?

Sure sounds like the pull-down or input buffer is shorted to ground; probably doesn't make any difference but is it being used as input or output?

Hi Mike, only small diesel engines - small bulldozer in fact. Yes, tried swapping with Tezza's. If memory serves me right (there was masses of faultfinding at Tezza's yesterday, he might be able to correct this), Tezza's 8049 in my keyboard produce several garbled chars for every keypress. It was then we noticed his board contained an external ROM, so concluded there must be different versions. Not sure if we tried my (faulty) 8049 in his good keyboard? (Tezza help me out here, please)

It's being used as an input. I thought maybe reducing the external pull-up resistor I added, to say a few k ohm to really crank some current thru there - might free it up! (Would if it was a mechanical system )

Philip

 

[MikeS]

Well, pretty drastic but if there are no other options I suppose it might work; I assume you mean to burn out the pull-down transistor and replace it with an external resistor? Of course it could be the FF driving it that's stuck, or the input buffer.

I assume when it's disconnected the other keys work?

 

[pavery]

Well, pretty drastic but if there are no other options I suppose it might work; I assume you mean to burn out the pull-down transistor and replace it with an external resistor? Of course it could be the FF driving it that's stuck, or the input buffer.

I agree, more current isn't going to fix internal faults like that. I'll wait to see if anymore ideas are forthcoming before I get drastic.

I assume when it's disconnected the other keys work?

No, no. Because the fault is within the 8049 - it detects the port is active all the time - irrespective of whether it's connected to the keys. So it's full-time auto repeat. Interestingly though, pressing another key (on another port) causes the auto-repeat to pause. I assume this is n-key roll-over code taking effect in the 8049.

Philip

 

[pavery]

It's possible to force the the 8049 to ignore its internal ROM and look for all respects like an 8039. Just raise the EA pin and all address references will be satisfied from external memory. My guess is that's what they're doing on Tezz's Kaypro.

Using an 8049 in this manner is also a way to re-use old, out-of-date 8049's that have already been programmed (rather than scrap them completely).

I getcha, Chuck(G). Arr, using up old 8049's - this makes sense. I guess it was a lot cheaper to add a ROM than buy a heap of new 8049's (which must have been quite expensive in their day).

Thanks
Philip

 

[MikeS]

No, no. Because the fault is within the 8049 - it detects the port is active all the time - irrespective of whether it's connected to the keys.
Philip

Duh! I knew that - don't know where that question came from. That's what I get for watching TV at the same time, and it's past my bedtime (my excuse & I'm stickin' to it ;-) )

Maybe Andrew's got some ideas; IIRC he adapted a Kaypro kbd to use with his Vector Graphic box (and now that he's got the S100 PS/2 kbd adapter he won't need it any more... ;-) )

 

[MikeS]

I getcha, Chuck(G). Arr, using up old 8049's - this makes sense. I guess it was a lot cheaper to add a ROM than buy a heap of new 8049's (which must have been quite expensive in their day).

Thanks
Philip

I got that, but how does it help? Seems to me Philip would have to add a ROM (and know the contents of the 8049 unless he could copy Tez's), not exactly trivial if, as I assume, there's no ROM socket in Philip's kbd?

 

[tezza]

What? You mean my keyboard circuit was old and out-of-date even for it's day and hacked around to make it work with new chips?! Hurumph...

Hmm...I don't think we tried your 8049 IC in my keyboard Philip. From memory we tried my keyboard on your machine and my IC in your keyboard.

Tezza

 

[Chuck(G)]

If you look at the datasheet, you'll see that, unlike the 8051, the 8049 has no privacy fuses, so the program can be read out. And, the good news is that 8749s are still available, although I don't know about your corner of the globe.

 

[MikeS]

If you look at the datasheet, you'll see that, unlike the 8051, the 8049 has no privacy fuses, so the program can be read out. And, the good news is that 8749s are still available, although I don't know about your corner of the globe.

Now that does sound like good news; if Philip has a compatible programmer he should be in business.

 

[dave_m]

Chuck, nice find. I didn't know ACP had any.

Philip:
I live close to ACP Surplus. I'll grab an 8749 just in case. I have a Data I/O PROM burner that is supposed to handle the chip except that the Unpak2B on it needs something called a 351B-070B adapter which I have been looking for a long time. It is the same adapter needed for the 8748 chip and I have a few of those chips that I would really like to be able to program. Maybe someone else is able to program the 8749 right away??
-Dave

 

[pavery]

Chuck, nice find. I didn't know ACP had any.

Philip:
I live close to ACP Surplus. I'll grab an 8749 just in case. I have a Data I/O PROM burner that is supposed to handle the chip except that the Unpak2B on it needs something called a 351B-070B adapter which I have been looking for a long time. It is the same adapter needed for the 8748 chip and I have a few of those chips that I would really like to be able to program. Maybe someone else is able to program the 8749 right away??
-Dave

Chuck: Thanks for sussing out the 8749 as an alternative. Wow, ACP certainly has a lot of stuff.

Dave: That's a kind offer, thanks. Especially as I don't have a EPROM programmer of any form & that I know little about programming them as well. However it sounds like the 8749 is one of the more tricky ones to program. So I presumed my first option would be to try & find someone with old Kaypro keyboards about who could pull an 8049 for me - for payment of course.

However if someone is able to burn an 8749 for me, then that would be an even better option, in terms of long term reliability. One question: how do we get the code? Does a good 8049 need to be read by the burner? I'm not certain mine is good - but we could take that chance.

Thanks
Philip

 

[tezza]

However if someone is able to burn an 8749 for me, then that would be an even better option, in terms of long term reliability. One question: how do we get the code? Does a good 8049 need to be read by the burner? I'm not certain mine is good - but we could take that chance.

Would there be any way to get the code out of my keyboard ROM? The ROM IC itself is soldered not socketed so I imagine it wouldn't be easy to get the contents. It's not like it can be just plugged into a reader?

I wonder if anyone has dumped this keyboard ROM somewhere?

Regarding the possibility of your ROM being corrupt Philip, from our PET experience corrupt ROM code seems often be a series of repeating values. If you (or someone) did manange to read your ROM with a reader, an examination of the extracted code may reveal some clues as to whether or not it's ok?

In saying that, there must be plenty of old unused Kaypro II keyboards around. All you need is a 8049 from one that's the same as yours. Anyone reading this got a junk one they could pull an IC from?

Tez

 

[dave_m]

The ROM IC itself is soldered not socketed

Ouch, I assumed that it was on a socket. So they have the 8049 on a socket, but not its repair ROM??

OK, then Tez's ROM can not be used. Too risky to unsolder a 30 year old 24 pin chip. Philip's 8049 ROM contents may be good if the problem is just a bad I/O input pin. The Data I/O can read it out, and hopefully other types of programmers. Perhaps a simple kludge can be built with a 40 pin socket to hold the chip and read it out and save the data as a 2K binary file.

Of course if an old keyboard can be found for a fair price, that will work too.

 

[Chuck(G)]

Surely, there must be a Kaypro owner on this side of the Pacific who wouldn't mind lending Dave his keyboard for a short time.

Anyone?