600XL with keyboard issues?

[bfollowell]

I started the thread about whether to keep the modulator in a 600XL that I'd purchased, assuming I was able to get it running, and therefore deem it worthy of installing a UAV and a monitor port. For what it's worth, I've decided to keep the modulator intact and only remove the channel selector switch to install the monitor port.

 

I finally received the RCA Male to F-Type Female Adapter I'd ordered and was able to check out my 600XL. It came in without an Antic chip, but when I put in one from another machine, it boots up just fine. The keyboard is a completely different issue. I don't seem to get any input from any of the keys except for Reset, Select, Option, Start, and Help, and they all stick when you press them and have to be pried up ever so slightly with a small screwdriver or something along those lines. So, basic operation looks good, but it has keyboard issues that need to be worked out.

 

I took a little break after typing this and investigated a little further and the mystery deepens. First of all, the keyboard appears to be all but dead. I do get a red power LED on it, and Reset, Select, Option, Start, and Help all work, but I get absolutely nothing from any of the other keys; not a single one. Here's where it gets strange. So, I pull out a known good keyboard; one that I verified before and after hooking it up on this 600XL. When using that keyboard, only about half of the keys seem to work. I've listed the non-working keys below. Again, I want to emphasize that this is a good keyboard. I verified every key works perfectly before and after checking it out on this 600XL. What I need to do, but haven't yet, and probably won't tonight, is check out the flakey keyboard that came with this machine in another working machine.

 

So, I haven't really investigated any keyboard issues before. Is it POKEY or the PIA that controls keyboard input? Sound seems good, at least in the basic built-in self-tests, so I don't suspect the POKEY, but there are definitely keyboard issues that are caused by the computer itself and not the keyboard.

 

Any ideas?

 

Thanks.

 

- Byron

 

 

Non-Working Keys

7 8 9 0 < > BS BR TAB Q W E R T Y A S D F G H CAPS N M , . / INVERSE SPACE

[StickJock]

POKEY (Potentiometer Keyboard) controls the keyboard (not counting start, select, option).

 

Looking at the key matrix and your non-working keys, it appears as if pins 1, 4, 6 & 7 are not functioning. All of the keys that you mentioned are on the key matrix rows associated with those pins.

 

You may have some cracked traces on the keyboard mylar, or less likely, cracked traces or solder joints on the PCB.

[zylon]

often, cleaning the large ribbon connector pads helps. I've even trimmed it back to use "new" surfaces on a couple.

[bfollowell]

11 minutes ago, StickJock said:

POKEY (Potentiometer Keyboard) controls the keyboard (not counting start, select, option).

 

Looking at the key matrix and your non-working keys, it appears as if pins 1, 4, 6 & 7 are not functioning. All of the keys that you mentioned are on the key matrix rows associated with those pins.

 

You may have some cracked traces on the keyboard mylar, or less likely, cracked traces or solder joints on the PCB.

When you say those pins, you mean pounds on the Pokey chip?

 

I think that's the most likely issue. There's nothing wrong with the keyboard mylar or the keyboard PCB, at least the one I used to check out the 600XL. It's a fully functioning keyboard, except when in this 600XL. Or did I misunderstand what you meant?

 

[bfollowell]

10 minutes ago, zylon said:

often, cleaning the large ribbon connector pads helps. I've even trimmed it back to use "new" surfaces on a couple.

I'm assuming you meant with the original keyboard that is mostly dead? I may give that a try after I check it out in another working machine.

 

As far as the keyboard where only half the keys are working, it is a good keyboard. There's really no issue with it. The issue appears to be with the computer itself.

 

I'm going to try swapping the Pokey chip out tomorrow too and see how that affects things.

 

[bfollowell]

A little more information. I did try that original defective keyboard with a known good 800XL. It acts the same. No key functions except for Reset, Select, Option, Start, and Help.

 

So, I decided to try swapping in a known good Pokey chip from known good 800XL. When I install the new Pokey, the 600XL won't boot. The TV gets a signal, but only displays a black screen. There's no life, no sound, nothing from the 600XL. It goes back to booting, but with the wacky keyboard shenanigans as before with a good keyboard. Are there any different Pokeys? Aren't they all pretty much interchangeable?

 

 

[StickJock]

13 hours ago, bfollowell said:

When you say those pins, you mean pounds on the Pokey chip?

 

I think that's the most likely issue. There's nothing wrong with the keyboard mylar or the keyboard PCB, at least the one I used to check out the 600XL. It's a fully functioning keyboard, except when in this 600XL. Or did I misunderstand what you meant?

 

No, I was referring to the pins on the keyboard connector.  But you say that it is a working keyboard, so let's follow the circuit path.

 

The keyboard connects traces between it's matrix's rows & columns.  These traces go to a long, single-sided connector on the PCB.  Check that all of the fingers are clean and making good contact.  Check that there are no cold or cracked solder joints on this connector. 

From the connector, the signals go to a pair of 4051 chips.  Swap these two chips around and see if the behavior changes.  If so, replace the chip(s). Beep out (test for continuity & low resistance) from the chip pins to the mylar.  This will verify that the signal goes from the chips, to the sockets, to the PCB to the keyboard connector, to the keyboard.  See a schematic for which pins to go to where.  I believe that the keyboard pins may have moved around  between the various iterations of 8-bit systems, so check an XL schematic.  From the 4051s, the signals go to the POKEY.  Beep from the 4051 pins to the pokey pins, which will show that those sockets & traces are good.

 

Looking at the schematic, it seems that those 4 keyboard traces are all going to the same 4051, U25, so if your keyboard is known good, that may be the culprit.  They go to X0, X1, X2, X3, which the chip would report on pins ABC as values 0..3 to POKEY's K3, K4, K5.  If the output to K5 were stuck high, then outputs 0..3 would show up as 4..7, but I would expect you to get some wrong keys instead of all dead keys.

 

Anyway, clean the sockets & check for continuity.  Swap the two 4051s around (U24 & U25).

 

I just noticed that there are some resistor networks in between the 4051s & the keyboard.  The schematics that I am looking at don't show the values for them, but take these into account when checking for continuity.  If the resistance is too high, you may not be able to just "beep" out the continuity from end-to-end.

 

Good luck!

 

 

[+DrVenkman]

13 hours ago, bfollowell said:

Are there any different Pokeys? Aren't they all pretty much interchangeable?

All POKEY chips are interchangeable. Compare the two POKEYs side by side, looking on-end along the rows of IC legs - any of them bent in? It could be causing poor contact when inserted in the socket; Atari's original single-wipe factory sockets are prone to getting bent, dirty or corroded contacts which can cause issues. I've run into this myself on more than one machine.

[SS]

The issue has *got* to be an issue with the keyboard ribbon cable then, doesn't it? 

 

I have an Alps keyboard with a defective ribbon cable myself.  I know that people have created whole new mylars and cables for the Stackpole type keyboards.  I wonder if I could just get a cable to splice onto my existing one?

[bfollowell]

52 minutes ago, SS said:

The issue has *got* to be an issue with the keyboard ribbon cable then, doesn't it? 

 

I have an Alps keyboard with a defective ribbon cable myself.  I know that people have created whole new mylars and cables for the Stackpole type keyboards.  I wonder if I could just get a cable to splice onto my existing one?

I really don't see how it could possibly be anything to do with the keyboard ribbon cable, or anything to do with the keyboard itself at all. Like I've said a couple of times, this is a known good, perfectly working keyboard from another computer, that was checked before and after trying it in this problem 600XL. It fails in the same way every single time in this particular 600XL, and consistently works perfectly in a known good machine.

 

I only installed this keyboard in this 600XL to try and narrow down initial keyboard issues when I first powered on the 600XL and could get almost no keys to work. Further investigation has confirmed the original keyboard that came with this 600XL definitely has issues and will need more troubleshooting of it's own. However, in addition to coming with a bad keyboard, this 600XL is also having keyboard issues when using a good keyboard with it. Now, whether this is a connector issue, keyboard connector issue, POKEY issue, or some completely different issue has yet to be determined.

 

Hopefully, I'll get some time for a little more in-depth troubleshooting this week, in between work and Grandpa time. I think I'm going to start by moving the 4051 chips from my suspect machine to a good one to see if the problem moves. Hopefully, that'll help me narrow this issue down a little bit. I'll check out the sockets and look for any evidence of problems there, as well as checking out the pins on the chips.

 

Thanks for the advice guys! I'll post back here with what I find, if anything.

 

[mimo]

Swapping the 4051's would be my next move 

[archeocomp]

I had both the connector on the motherboard and the keyboard cable (green type) gone bad in my 600XL.

 

[bfollowell]

Yeah, that is strange, but I have two unrelated keyboard issues in one computer. One, a mostly dead keyboard, and two, some other motherboard-side keyboard issue. What are the odds?

 

Edited December 13, 2020 by bfollowell

[bfollowell]

Well, I've had partial success. So, so far, it looks like this 600XL came with no ANTIC chip, a defective keyboard, and a faulty 4051 chip in position U23.

 

Now I just need to disassemble, clean, and troubleshoot the keyboard, to see if I can revive it.

 

Before too long, I'll need to order a UAV, a monitor port, an ANTIC chip and some 4051s. Hopefully, I'll be able to get the keyboard going again.