After some advice on Keyboard re-set and an external FDD.

[Capt Mustard]

Dug my Amiga out after 20 years, got an RGB to SCART cable and I have sound and Gfx. I pulled it apart, aside from some early 90's dust it looked as new, absolutely no Capacitor leak. I do have two issues though. Keyboard re-set not working. External FDD no power. I am thinking get some contact cleaner, spray into the Floppy Disk Port and the On/Off switch of the external caddy. Get some 99% Alcohol and clean the Keyboard membrane. If neither of those solves the issues does anyone have any advice for the next step? If I buy a Voltmeter, can I test where the re-set signal is going amiss? And can I check if there is voltage leaving the Floppy Port on the rear of the Amiga? Not exactly PC plug and Play are they, terrified of breaking it, kid gloves. Thanks.

[solarmon]

What Amiga is it - model and revision.

Don't use IPA on the keyboard membrane - it will degrade the coating on it.

A multimeter is a very good investment. Get an auto-ranging one and don't go for the cheapest you can find. So is a logic probe - especially for checking the reset signals. A multimeter is not suitable, or quick enough, to show the change in the reset signal.

[Capt Mustard]

Thanks for the reply, no IPA on the Keyboard, didn't see that coming, thanks. What is the consensus on cleaning it? Soapy water? It is an Amiga 500. I think it is Rev6 (1989) I would have to pull it apart to confirm (I will). I literally went from no interest to completely hooked within a few days, determined to get it back up and running.

[Jope]

I just use a kitchen paper towel with a tiny bit of water on it. You know, not soaked, but enough that it actually glides over the membrane. Give it a gentle wipe, then pat it down with dry paper towels.

[Capt Mustard]

It is an Amiga 500 - Rev 6A (Manufactured 1989)

External drive has come back to life by just flicking the On/Off switch back n forth a few times, and pulling all the cables on and off a few times (with power off) - I figured might just be bad connections with sitting.

Pulled the Keyboard apart, the membrane looks as new, little bit of dust. Did the damp paper towel method, a little bit of dirt came off, not loads though. Keyboard still working in general, the Caps Lock light is working, can manoeuvre through menus, but still no go with CTRL-A-A re-set.

Are there any simple tests (using a multimeter, not ordered one yet) to show where the signal is going amiss. I did read a post saying you can short the Re-set pin to earth as a test, but I am not so sure I fancy trying that. If it was a PC I would have no issues.

If this is of any use....before I put it back together.

Mitsumi Keyboard- PCB A500 - 56 A620A - (MOS 6570-036 1985 CBM 3888 14) - (HD74LS27P) - (HD74LS123P) - (HA17555 8H4)

[solarmon]

I've put together some diagrams for the reset signals to help me troubleshoot. You may find it useful too.

https://sites.google.com/one-n.co.uk...-reset-signals

[Capt Mustard]

That's brilliant! Thanks.

[Daedalus]

For the reset not working, have you checked that the three keys work separately? If that's the case, but the reset isn't working, it could well be a fault on the keyboard. You can (carefully!) short the keyboard's reset pin to ground to see if that resets the machine. If that doesn't work, the fault is on the motherboard. If that does work, the fauld is on the keyboard PCB.

[Capt Mustard]

No, haven't tested the keys individually, I can't find my Workbench disks, I do have them. Unless there is another way to test them? I assumed I will need a txt editor of some kind? Tbh, so long since I have seen Workbench I can't remember what it comes with.

I did see something about shorting the keyboard re-set, played it safe and ordered a Logic Probe. Will probably try that if all else fails.

Thanks for the reply.

[Jope]

If you boot the machine into a CLI, you can test them.

CTRL can be tested with CTRL-I (tab) or CTRL-M (return).

The Amiga keys can be tested by holding down either Amiga key and the left or right Alt key. Left side of the space bar is left mouse button, the right side is the right button. (try dragging the window around with LAmigaLAlt or watch the top of the screen turn blank when the menu is opened by holding RAmigaRalt.

If one of the Alts or Amigas is broken, you can still mix and match the Amigas and Alts to see which is dead.

[Capt Mustard]

Logic Probe should arrive next week. And I still can't find my Workbench Disks. In the meantime I have been having a look at Schematics and Solarmon's block Diagram. Was wondering, I see CTRL and A A sit on pins 23,26 and 27 of the 6570. With a Probe on those pins, if I press the key will/should I see a change on the probe?

[solarmon]

Yes, those system keys are active low, meaning that they will go low when the key is pressed. You will see the pin go low using the logic probe. When all three of those pins are low(i.e you just did a CTRL-A-A) then the _KBRESET signal will be asserted low, causing a reset signal to be sent to all the other chips.

[Capt Mustard]

Found Workbench (right on queue as Logic Probe and Multi-Meter get delivered).

1: Based on what Jope suggested......

CTRL and "M" or "I", gives me a white box around "I" and a return on "M".
Left ALT/Right Amiga Key grabs the window.
Right ALT/Right Amiga Key makes the top bar turn white - if I do Amiga key and then ALT it will flash the lettering. If I do ALT then Amiga it will turn top bar permanent white till I let go.

Looks like my issue is left Amiga Key, not doing a thing. I can re-check the membrane, but it looked spotless to me.

2: Does anyone have advice on a good place to connect the Logic Probe, am really struggling to find VCC and Ground for these Crocodile clips. Can you suggest something on the Mainboard that will give me a bit more purchase.

Thanks again.

Now I have Notepad running, looks like I have a faulty Left Amiga key and a faulty Numpad No3. Everything else is working.

[Capt Mustard]

I will start afresh or that last post is going to get a bit muddled.

I have my meter set to Continuity, I have one probe on Pin26 of the 6570, one probe to ground. When I press CTRL, I get a number on the display. Then did the same thing via Pin4 of IC2-B. When I press CTRL, I get a number. I did the same thing with Right Amiga, Pin27 and Pin5. I get a reading when I press Right Amiga key.

I tried the same thing with Pin3 of IC2-B, Left Amiga, I get nothing. So I went back to Pin23 of the 6570, and I get nothing.

Looking on the membrane, one of the pads for Left Amiga key is joined directly to three other pads, I think it is Left ALT, Left Shift and CTRL. I get continuity between all those pads. That at least suggests that pad on the Amiga key is good. Then I swapped the plunger on the Amiga keys, and no change, but at least I know that isn't the problem.

Killing my eyes trying to track these wires through the membrane. I need a break.

Found a membrane layout I can understand (ish) (made by user Nocash) - set to continuity, I am across Pin1 and Pin7, I get a display via V,F,R and F3, but not Numpad3.

[Capt Mustard]

I think the Membrane is the issue after all that. I grabbed the Membrane picture provided by Solarmon (thanks for that).

Numpad3 has no continuity to Pin19/Y10 - all other keys using that track are working as per previous post, so must have a break between the pad and the junction for Y10. I found one small square that is slightly different colour, could be that. Tbh I can see the same thing on almost all the tracks and they are working fine, so I dunno.

Left Amiga to Pin14 of the connector, no continuity at all.

[Jope]

There's your problem.

The qualifiers all have direct lines, so any problems with those keys are isolated to that one key. The rest of the keys are in a matrix, so usually several keys die at the same time if there are continuity breaks in the membrane.

[solarmon]

@Capt Mustard

The usual damage on the membranes are the traces underneath the space bar - specially where the plastic supports are and where there is a hole in the plastic board (that lets in dirt, grime and other nasty stuff). But there are many other places where there are traces going underneath the plastic supports.

Also, if there are any dark looking places on the traces then it has probably corroded and the trace is broken - so look out for that.

Can you show a picture of your membrane. What type is it? A619A or A619B?

[Capt Mustard]

It's an A619A

What I noticed is there seems to be a lot of areas that are darker in colour. I think I found the break in the track that has killed the Numpad 3 (red circle).

I have ordered a replacement Membrane.

It's not really showing up on those pics, the full size versions are 4Mb though, but even those don't really pick it up. With the naked eye it really shows up. It is a brownish tint to almost all of the tracks. The box smells damp, I am wondering if some moisture has got between the layers of the membrane and is starting to eat it away? The motherboard, getting a bit more ventilation may have escaped? I am guessing.

[Capt Mustard]

This one shows it better.

[Capt Mustard]

Got the new Membrane, everything working fine. Thanks to everyone that offered advice.