Partly working keyboard

12 posts / 0 new
Last post
Offline
Last seen: 1 week 4 days ago
Joined: Sep 26 2019 - 16:46
Posts: 11
Partly working keyboard

Having spent some time searching for an Apple ][ related forum I finally found this site, which I'm glad I did!

 

I'm trying to revive an old Apple ][+ (actually an Asian clone) and after cleaning it up (removing corrosion), re-soldering some cold joints and changing a 74LS74 I now have the familiar "Apple ][", the cursor and beep. However, the keyboard doesn't work -or rather: CTRL-RESET is the only thing that works! There's no reaction from the other keys.

 

So the big question is (before I spend a great deal of time troubleshooting in the wrong area): since CTRL-RESET works (or just RESET -there's a switch on its circuit board which allows you to choose one or the other way of doing a reset), would this indicate that the keyboard is malfunctioning, or something inside the computer? I don't know how the keyboard works, but could it be that CTRL-RESET are hardwired directly to the computer (i.e. the 14 pin keyboard connector that goes into the II+ motherboard) while rest of the keys have to go through the keyboard controller circuitry (on the keyboard PCB)?

 

 

The rest of the computer appears to be working as it should, but I really can't say for sure since I don't have a second system to compare with, and the floppy disks are all 25-30 years or more old. Just about none of them booted excpt for "Apple Cillin" which presented on the screen a number of hardware tests. So at least that should verify the disk controller (slot #6) and 5.25" floppy drive works. For all I know the issue with the other floppies could be a disk alignment issue, but I don't want to look into that before I get to fix the keyboard. 

So where to start troubleshooting and how?

Offline
Last seen: 2 weeks 6 days ago
Joined: Sep 30 2019 - 23:01
Posts: 1
Just wanted to say I'm having

Just wanted to say I'm having this exact problem, too, but wanted to add a little bit more info for my situation, which may apply to yours as well:

  • The self-diagnostic (CTRL-OPEN-CLOSE-RESET) works fine and results in "KERNEL OK"
  • Disks work and I can load into games and things fine

Just no keyboard input works.

 

 

Online
Last seen: 20 min 36 sec ago
Joined: Jul 5 2016 - 19:01
Posts: 36
You are correct, Ctrl-reset

Fuji: You are correct, Ctrl-reset bypasses the keyboard encoder.  If the other keys are not working I would be checking the keyboard PCB, specifically the keyboard encoder IC.  Genuine apple ][+ encoders are Apple specific so a little hard to find unless someone is parting out a machine - chances are if it's a clone they will be using a generic encoder so you might have more luck finding one.

 

Tranicos: sounds like you have a Apple 2e - strange as CTRL-OPEN-CLOSE-RESET combitnation work.  The 2e uses the AY-5-3600-PRO encoder and replacements are available on ebay etc so you might want to try a replacement.

Offline
Last seen: 1 week 4 days ago
Joined: Sep 26 2019 - 16:46
Posts: 11
Thanks for your comments and

Thanks for your comments and confirming that CTRL-RESET bypasses the keyboard encoder.

At least the computer appears OK! Good to hear that the encoders are still available. Mine is marked as follows:

 

KR3600-017

SMC  8301C

KR3600-PRO

 

So is this the same "3600-PRO" you said the IIe used?
I see there's a total of 6 ICs on my keyboard PCB:

  • 3600-PRO keyboard encoder
  • 74LS123 (the only socketed TTL chip)
  • 74LS00
  • 74LS08 (2 pcs)
  • 2716 EPROM

 

The keyboard has a caps-lock button with a red LED inside (if I recall correctly it only made a difference in 80-col. mode where I was able to switch between upper/lower case). And on the left hand side there's a 2-position switch for making reset possible with just the RESET key or with CTRL-RESET (my choice). There's no brand name on the keyboard or anything except for "KEY BOARD" on the component side and "SYKB-001H" on the solder side, but I haven't been able to find anything online concerning it, so there aren't any helpful schematics or other info to be found. I've always been under the assumption that the keyboard wasn't an Apple clone, but rather an "Apple II compatible" keyboard. Regardless, I've so far not been able to find an Apple II keyboard schematic either.

 

By the way, what is the EPROM for? I thought the keyboard encoder handled all the characters, and the actual characters seen on the screen handled by the keyboard generator EPROM on the Apple II motherboard. I hear that EPROMs go bad after a number of years, so if that's happened here -are these keyboard EPROMs generic, or does each keyboard have their own EPROM? I do have an EPROM programmer, so perhaps I should just pop out that 2716 and read/save its data as soon as I can.

Online
Last seen: 20 min 36 sec ago
Joined: Jul 5 2016 - 19:01
Posts: 36
Hi,

Hi,

Yes the KR3600-017 is the same as what the Apple 2e uses.

You can find the encoder pinout online and check if you have activity at the input / output pins to confirm if it's actually the fault. It is also possible one or more of the 74LS ic's are causing the problem - they can be damaged simply by connecting the cable between the keyboard and motherboard the wrong way.

You are correct how the regular apple II keyboard works, I'm not familiar with clones so I'm not sure what function the EPROM may be performing except perhaps remapping keys?

As long as the window on the EPROM is covered it should be ok however if you have a programmer it can't hurt to take a backup.

There is a few different versions of the Apple II keyboard, schematics are available online in various books such as Understanding the Apple ii.

Offline
Last seen: 1 week 4 days ago
Joined: Sep 26 2019 - 16:46
Posts: 11
dc99 wrote:Hi, Yes the KR3600

dc99 wrote:
Hi, Yes the KR3600-017 is the same as what the Apple 2e uses. You can find the encoder pinout online and check if you have activity at the input / output pins to confirm if it's actually the fault.

 

I found the datasheet at an Apple II related website here. That's a good suggestion. I suppose my simple DIY hobby oscilloscope (Jye tech DSO-150) might suffice for this?. eBay has several KR3600-xx chips for sale, but none of them have the -17 suffix. Is it the same as the -PRO? Assuming that since it actually also says "KR3600-PRO" on my chip.

 

Quote:

It is also possible one or more of the 74LS ic's are causing the problem - they can be damaged simply by connecting the cable between the keyboard and motherboard the wrong way.

 

Yes, that could very well have happened -actually I'm sure I've put the cable the wrong way round, so maybe I should just desolder all the TTLs (LS08, LS00), solder back in sockets and replace them all (including the LS123). Any other component which I should look out for? I know electrolytic capacitors dry up after a while, so maybe I should replace the two I've found?
I assume as long as the red caps lock/power LED lights up on the keyboard and CTRL-RESET works I have at least got the cable the right way round.

 

Quote:

You are correct how the regular apple II keyboard works, I'm not familiar with clones so I'm not sure what function the EPROM may be performing except perhaps remapping keys? As long as the window on the EPROM is covered it should be ok however if you have a programmer it can't hurt to take a backup. There is a few different versions of the Apple II keyboard, schematics are available online in various books such as Understanding the Apple ii.

 

Good suggestion. Fortunately the computer's EPROMs are available online, but throughout all these years I never thought about backing up the keyboard EPROM. I might have borrowed a buddy's Apple II back in the day in order to read/save the keyboard EPROM using my Apple II-based EPROM programmer, but those are all saved on 5.25" floppies, so at the moment it's a catch-22, and for all I know the actual disk may not even be readable by now. Oh well.

Online
Last seen: 20 min 36 sec ago
Joined: Jul 5 2016 - 19:01
Posts: 36
If you had the cable around

If you had the cable around the wrong way I would start by testing (or replacing) the 74LS ic's - try the 74LS08's first as one of those is what I found failed in a similar situation

My 2e has exactly the same labelled keyboard encoder as your so you should be fine replacing it with a "AY-5-3600-PRO" if necessary.

Your scope should be fine to test these components.

Offline
Last seen: 1 week 4 days ago
Joined: Sep 26 2019 - 16:46
Posts: 11
dc99 wrote:If you had the

dc99 wrote:
If you had the cable around the wrong way I would start by testing (or replacing) the 74LS ic's - try the 74LS08's first as one of those is what I found failed in a similar situation My 2e has exactly the same labelled keyboard encoder as your so you should be fine replacing it with a "AY-5-3600-PRO" if necessary. Your scope should be fine to test these components.

 

Well, I successfully managed to desolder the two 74LS08 and the 74LS00, replacing them with IC sockets and new chips, but still no go. No difference from before. That leaves the 74LS123 (monostable multivibrator), the KR3600-PRO encoder and finally the 2716 EPROM (I have no idea what to program a new one with in case it's faulty). I couldn't get any output on my scope, so my guess is that the encoder is broken or I just haven't got the hang of using it properly.

 

I'm about to order a 74LS123, the AY-5-3600-PRO and a couple of 10uF/16V electrolytic capacitors (the only electrolytics in the keyboard) as it's not impossible these might be dried out after 35 years or so.

I'm a little confused about the encoder chip though... according to this Apple II page, the KR3600 isn't compatible with the above:

Quote:
The KR3600 decoderchip sound quite similar to AY-5-3600 but it isn´t similar at all ! But it was acommon used chip in third-party keyboards.

and furthermore it confuses me that my keyboard decoder is marked "KR3600-17" as well as "KR3600-PRO". If I'm not mistaken, from what I've read the "-PRO" extension means it's programmed with a standardized key-table while the other extension numbers means it's got one of a number of different customized key-tables ordered by the company who's designed the keyboard in question. So how can it be both? Can anyone enlighten me on this?

In any case it's not much of an outlay so I'm ordering the AY-5-3600-PRO to see what happens in case replacing the other parts doesn't solve my problem.

 

 

Offline
Last seen: 8 hours 52 min ago
Joined: Jun 5 2008 - 07:26
Posts: 420
On a normal Apple II/IIe

On a normal Apple II/IIe keyboard. plugging the keyboard in wrong invariably kills the 7404 that is connected to -12 volts on the keyboard socket.  I'm not sure how this clone keyboard is wired, but I would expect a similar result.

 

regards,

Mike Willegal

Offline
Last seen: 1 week 4 days ago
Joined: Sep 26 2019 - 16:46
Posts: 11
There's no 7404 (or 74LS04)

There's no 7404 (or 74LS04) on the keyboard PCB here unfortunately. The two 74LS08 chips appear to be closest to the keyboard socket, and they've both been replaced with no difference.

Are there any ICs on the II+ motherboard which are directly related to all of this which I could try replacing?

 

Online
Last seen: 20 min 36 sec ago
Joined: Jul 5 2016 - 19:01
Posts: 36
Hi,

Hi,

1. I double checked and in my early 2e version it has a KR3600-017 labelled chip in the keyboard encoder socket which is labelled on the board as AY3600-PRO so I'm fairly certain you will be fine with the AY-5-3600-PRO.

2. If for some reason this doesn't work these encoders have the same pinouts but different key mappings so the worse case is you will press a key and another one will be displayed. At least the you will be able to confirm if it's the encoder or not.

3. Perhaps you can try using your scope on a simple 74LS chip on your motherboard which is working to see if your using it properly.

Offline
Last seen: 1 week 4 days ago
Joined: Sep 26 2019 - 16:46
Posts: 11
Thanks for double checking

Thanks for double checking the encoder. Seems like it's the same one as I have!

Yes, I'm thinking the same about the encoder -at least something will come up on the screen when I press the keys, so I can confirm that the encoder needs replacing.

Good idea about checking a simple TTL chip with the scope -I'll give it a go. So next off is ordering the AY-5-3600-PRO (I found sellers of these on eBay in case someone else is in need of the same).

Log in or register to post comments