(A500+) more keyboard problems

[sim085]

Hi,

I already had another thread on my A500+ keyboard. However things have taken a bad turn it seems.

When I switched my A500+ after a long time I realised that the keys CTRL+AmigaL+AmigaR where not restarting my machine. However as much as I remember all keys worked fine when not in that combination.

After that I once plugged in my joystick while the machine was turned on. Something must have happened then. The CTRL+AmigaL+AmigaR worked once. Then when the machine re-booted and tried again the Capslock button would no longer work for a few seconds and then again it would start to work. The CTRL+AmigaL+AmigaR never worked again (but my joystick has no problems).

I then shelved the concerns I had on my keyboard while I started buying new equipment for my machine. Yesterday I decided to look back into the issue. However now I noticed that the ShiftL and AmigaL keys do not work.  

I do not know what the problem might be. However before this I had confirmed that the transistor responsible for reset was not working.

Does anyone have any idea what I need to do... I can buy a new keyboard but I prefer if I could fix what I have already - I had to have to throw anything Amiga ... even when it does not work!

[Lockon_15]

Left Shift and left Amiga key could share same bus contact and perhaps if their common trace is damaged, that could be the reason for that local malfunction.
Dissasemble keyboard in pieces and try to take a look at thin black traces on both inner parts of keyboard matrix. Sometimes an excess dirt could cause printed conductive trace to lift-off and thus result in defect of more keys together.

Did you replace that dead transistor ?
IMHO, both of those on that small PCB can be replaced with 2N3904 or maybe 2N 3906, not sure exactly which type is (NPN or PNP).

[sim085]

Lockon_15 wrote:
Left Shift and left Amiga key could share same bus contact and perhaps if their common trace is damaged, that could be the reason for that local malfunction.
Dissasemble keyboard in pieces and try to take a look at thin black traces on both inner parts of keyboard matrix. Sometimes an excess dirt could cause printed conductive trace to lift-off and thus result in defect of more keys together.

I will try to do this. So do I have only to clean where I see dirt? Additionally, from what do I determine if a trace is damaged or not?

Lockon_15 wrote:
Did you replace that dead transistor ?
IMHO, both of those on that small PCB can be replaced with 2N3904 or maybe 2N 3906, not sure exactly which type is (NPN or PNP).

I still did not do this because I need my cousin for this since I do not have any experience with soldering. I was going to try and find those transistors from a local store.

[Lockon_15]

Traces are printed on each transparent plastic foil in the way that each trace on one side stay safe from traces on the opposite side, when both foild are strapped together (justs like sandwich).

You should track that traces in close vicinity of mentioned keys and check if some part of trace is damaged, missing or got moved to opposite foil (I had exactly that kind of issue last month).

[sim085]

if parts of the trace is damage, missing or got moved to opposite foild then what do I do?

[Lockon_15]

You have to compensate for that, i.e. make sure to establish good conductive properties of that failed line(s).

In short, get a pen with conductive ink - many electronic stores have it. Then make two or three thick passes until you get a visible, dense line, again.

Or maybe just get a spare keyboard (without keys and metal casing, to reduce cost on freight). You need small PCB - printed circuit board (stuff in upper right corner which connects to A500 motherboard) and plastic membrane/foil which can be detached/attached from PCB and rolled for smaller package format.

[Metalguy66]

Yeah one brand of conductive-Ink pen is called "CircuitWriter"...  Fry's stores usually carry it for about $10.00 (which is a total rip-off, but we are talking about fry's here.)... You may be able to find it cheaper on the web.

I have also seen people use a regular #2 graphite pencil to temporarily repair hairline cracks in traces on those "mylar printed circuits"....

[sim085]

Thanks, I'll try to open the keyboard this evening and see what the problem might be!

[Zac67]

Unlike with other Amigas, the A500(+) generates _KBRESET within the keyboard - thus if the keys Ctrl, AmigaL, AmigaR work by themselves, it must be this _KBRESET line that's broken and not the keys.

Start on pin 3 (pin 5 is keyed) and follow it back to the keyboard controller or to JP1/Q711 on the mobo and Gary's pin 5.

[sim085]

I opened the keyboard. There was some dirt cleaned it. Closed it again, but the Amiga-Left, Shift and Ctrl still do not want to work!! I checked the lines but did not see anything strange! Is there any other parts of the keyboard that could creating this problem? If not then I might considering ordering just the membrane of the keyboard!

[Lockon_15]

@Zac67

Yes, that's the proper procedure to follow, but he said last event showed left Shift and left Amiga keys are out. If he cannot work out on those issues, there's no point on getting feet wet on broken transistor or 74LS27, right ?

Replacing a dead Q2 isn't a big deal, but '27 could be a real PITA for a unskilled (un)solder attempt...

Best regards

[sim085]

Sorry to bring this up again, but; if it is not the membrane then could it be something else?

[Zac67]

Sorry, didn't read the posts thoroughly.

Apart from the membrane, it could be the I/O pin of the KB controller - but I've never ever had that. Make sure the membrane traces, its connector and the leads to the controller are AOK. Measure conductance of each separately, the keypress can be simulated with a copper coin.

Exchanging the controller might not be worth it as it's not available new (only unprogrammed) and would have to be salvaged.

[sim085]

Thank you I will try to use a multi-meter to see if there is any damage to the membrane. Thanks for now

[sim085]

Hello again,

I still did not confirm if the problem is with the membrane. However if so then could I just buy the membrane of an A500 keyboard rather then waiting for an A500+ one? or?

Regards,
Sim085