Trying to get XT/AT switchable Sejin EAT-1010 to work

[poobajones]

I have a Sejin EAT-1010 keyboard that has DIP switches on the bottom to choose between four modes: Auto (AT), Auto (XT), AT, and XT. I am trying to get it to work with my IBM 5150 PC. When I have it switched to XT mode and plug it in to my 5150, turning on the computer makes the three lights on the keyboard flash once quickly, but when the computer boots up, no keys will register. I don't get a 301 error. Pressing the scroll lock key will make the light on the keyboard come on (and pressing it again will turn it off). Num Lock and Caps Lock don't do anything. If I switch the keyboard to AT mode, the lights flash quickly again, but I do get a 301 error, and still no key presses registers anything at all on the screen. Connecting a PS/2 keyboard to the 5150 using an adapter does get keypresses to show on screen, though they are garbled due to the invalid protocol, but I believe the PC's keyboard port is good. This keyboard doesn't work in any mode when connected to any other machine I've tried it with either (AT or PS/2), so I think something about it is messed up. Is there any certain place to start troubleshooting an issue like this? I've attached a few photos for reference.

[joebeazelman]

It looks like the keyboard isn't working properly based on what you described. The only think I can recommend is to perform some basic inspections. If you have a multimeter, set it to continuity or resistance and test each pin from the plug to the wire connector at the keyboard. Second, visually inspect the keyboard PCB and look for any deformed or burned parts. Capacitors are most likely to fail after a certain amount of time. Check all of them and see if there are any leaks bulges splits etc.

On the last photo, there is an orange capacitor near the multicolor wire connector in between the two chips. It's partially obscured by a black capacitor and appears to have something brown on it. Find out if it's burned, leaking or if it's something else. Overall the keyboard looks like it was exposed to a humid place or was exposed to liquid. You can see the rust spots on parts of the keyboard. Where there's rust, there's corrosion. There's a possibility the damage might be more extensive than it appears.

[Palatino]

This keyboard doesn't work in any mode when connected to any other machine I've tried it with either (AT or PS/2), so I think something about it is messed up.

I think you’re right. I have the same board, albeit rebadged, and mine works on a PC with basic adapters. If you don’t make progress I could take some pictures of mine for comparison if that helps to locate the problem.

[TNT]

If you have the parts and don't mind the effort, I'd recommend just replacing all of the electrolytic capacitors. I've had two boards act up on me so far and every time it was an issue with an Elco. Those things don't age too well, it seems.

[Muirium]

Those things don't age too well, it seems.

They really don't. All electrolytics—especially those form the 1980s and 1990s—are suspect. They just love to pee the bed with their electrolytic ooze! Take a close look for it. The damn things are a curse.

Still need to recap my Macintosh SE/30 someday.

[poobajones]

Thanks for all the suggestions!

I took my multimeter and with the keyboard plugged in and computer turned on, measured 5 volts out of each solder joint except for the green wire which was 4.66 volts. The two electrolytic caps near the cable connector didn't look bulging or leaky to me, and I don't see residue on the board but I went ahead and replaced the one on the left since I had a new one on hand. It didn't seem to change anything though.

On the last photo, there is an orange capacitor near the multicolor wire connector in between the two chips. It's partially obscured by a black capacitor and appears to have something brown on it. Find out if it's burned, leaking or if it's something else.

You're right, there was some brown crusty stuff on this orange ceramic cap. I was able to scratch the stuff off, and don't see any cracks in that cap where it could've come from. I took my multimeter probes on each of its legs and tested 5V coming thru it (same with all the other caps on the board). Not sure if that indicates that they're good or not.

I found a replacement electrolytic cap for the right-side one that I can order for cheap, as well as some new orange ceramic ones. Is it worth replacing the ceramic caps as well as the electrolytic ones?

[hellothere]

On the last photo, there is an orange capacitor near the multicolor wire connector in between the two chips. It's partially obscured by a black capacitor and appears to have something brown on it. Find out if it's burned, leaking or if it's something else.

You're right, there was some brown crusty stuff on this orange ceramic cap.

That's the definition of a bad cap, really.

I don't know electronics very well, but I became acquainted with desoldering and replacing caps, in a past life.

[poobajones]

I've ordered the new caps. When they come in I'll do the replacement and see if that does the trick. Thanks

[Polecat]

Thanks for all the suggestions!

I took my multimeter and with the keyboard plugged in and computer turned on, measured 5 volts out of each solder joint except for the green wire which was 4.66 volts. The two electrolytic caps near the cable connector didn't look bulging or leaky to me, and I don't see residue on the board but I went ahead and replaced the one on the left since I had a new one on hand. It didn't seem to change anything though.

On the last photo, there is an orange capacitor near the multicolor wire connector in between the two chips. It's partially obscured by a black capacitor and appears to have something brown on it. Find out if it's burned, leaking or if it's something else.

You're right, there was some brown crusty stuff on this orange ceramic cap. I was able to scratch the stuff off, and don't see any cracks in that cap where it could've come from. I took my multimeter probes on each of its legs and tested 5V coming thru it (same with all the other caps on the board). Not sure if that indicates that they're good or not.

I found a replacement electrolytic cap for the right-side one that I can order for cheap, as well as some new orange ceramic ones. Is it worth replacing the ceramic caps as well as the electrolytic ones?

Monoceramic caps don't go bad as often as electrolytics, but they can and do go bad occasionally. Here's a thread from a while back where one went bad on a Focus keyboard:

viewtopic.php?f=7&t=24348

Testing caps with a multimeter doesn't tell you much unless you remove them from the PC board, because they are connected *across* other things, rather than having DC power passing through them. When disconnected they should show "open", or infinite resistance. If discolored or leaking something they are definitely suspect!

[poobajones]

Unfortunately, brand-new capacitors did not make any difference. Any last-ditch efforts to try before I see if I can return the board to the guy I got it from?