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intric8
Seattle, WA, USA
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Posted Thu Sep 20, 2018 11:43 am

Simply plugging in a joystick while the power is on can do it. Amiga Bill did that to his own 1200 a year or two ago.

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ClockworkCoder

Posted Thu Sep 20, 2018 11:48 am

intric8 wrote:Simply plugging in a joystick while the power is on can do it. Amiga Bill did that to his own 1200 a year or two ago.
Hmm... I'm usually pretty diligent about not doing that, but I guess it's possible.

You doubt that the problem is power supply related in this case? Are those chips hard to replace?

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intric8
Seattle, WA, USA
Website

Posted Thu Sep 20, 2018 12:04 pm

Not hard to replace but not sure about sourcing them. Looks like there is a place in the UK selling “new” ones. However this is but a guess on my part. I’d hate for you to go down some rabbit hole. Be so much better if you had a donor machine to swap things and see The results.

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ClockworkCoder

Posted Thu Sep 20, 2018 12:40 pm

Okay, I'll see if a replacement power supply helps first then. If nothing else I'm not really comfortable using the current one much knowing that it's not giving the output it should - I'm a little concerned that it could potentially cause a surge on its own.

As for the rabbit hole, I think I'm already half-way down it already! ;)

I was really just wanting to try some of the cool Gotec mods for the new firmware (rotary encoder, oled and piezo buzzer) originally though. It's all a good learning experience though.

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intric8
Seattle, WA, USA
Website

Posted Thu Sep 20, 2018 1:08 pm

It's worth noting that when I bought my A1200, the previous owner shipped it with an A500 PSU he was using as he claimed it "provided additional amps".

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ClockworkCoder

Posted Thu Sep 20, 2018 1:15 pm

Hmm... I hate to think what condition it is in now, but I believe I've got an A500 in the attic. Might be worth testing, although I'll make sure to test it before attempting to plug it in.

I'd read a while ago that the A500 power supplies were more powerful. Thanks for reminding me :)

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Zippy Zapp
CA, USA

Posted Thu Sep 20, 2018 7:27 pm

The top left pin (+12v) was fluctuating close to +1v
The middle pin (-12v) was fluctuating around -2.2v
The bottom-right pin (+5v) was pretty steady at 3.3v
So your PSU is measuring 1 volt on the 12 volt line?

Yeah there is for sure something wrong with either your PSU or your Multi-meter. Your Amiga should not function with 1 volt or I don't believe 3.3 volts either. Your PSU should be outputting at least 12 volts on the 12 volt line and at least 5 volts on the 5 volt pin. Possibly a bit higher if you are measuring it without any load.

Are you measuring those straight from the PSU connector or while your Amiga is turned on from the backside of the connector?

Hopefully it is not a CIA (VIA U7, U8 apparently). because those are surface mount ICs and I am sure they won't be easy to remove.
U7 is the one next to the Keyboard connector and handles KB_Data and KB_Clock, as well as mouse/joystick.

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ClockworkCoder

Posted Thu Sep 20, 2018 11:48 pm

Zippy Zapp wrote:
The top left pin (+12v) was fluctuating close to +1v
The middle pin (-12v) was fluctuating around -2.2v
The bottom-right pin (+5v) was pretty steady at 3.3v
So your PSU is measuring 1 volt on the 12 volt line?

Yeah there is for sure something wrong with either your PSU or your Multi-meter. Your Amiga should not function with 1 volt or I don't believe 3.3 volts either. Your PSU should be outputting at least 12 volts on the 12 volt line and at least 5 volts on the 5 volt pin. Possibly a bit higher if you are measuring it without any load.

Are you measuring those straight from the PSU connector or while your Amiga is turned on from the backside of the connector?
I doubt it's an issue with my multimeter; it's a pretty good one. I was measuring it direct from the connector (black on ground, and red on the other three pins alternately).

The 12v pins fluctuated wildly, making it hard to read - perhaps I need to use clips, rather than the probes to get better contact though... I'll check again later. Irrespective of that, I'm really still not confident about it - like I said, the 5v pin was stable each time I tested it (at 3.3v) which implies it wasn't something I was specifically doing.

If it does come to the CIA's, which I'm not keen on, I would attempt to fit sockets in their place (if there's space?). However, replacing the capacitors has given me a good awareness of how tricky removing old components can be...

Sometimes this all feels frustrating, especially as it seems like one step forward and two steps back, but I am learning a lot from it, and I'm gradually building confidence fixing other stuff too. I've already fixed some bathroom scales with no display, and a TV with volume that constantly wanted to go up or down of its own volition already :)

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ClockworkCoder

Posted Fri Sep 21, 2018 4:50 am

Another quick update. I re-checked the original supply, and it was much the same.

However, I checked the attic, and found my Amiga 500 power adapter, and checked that. It looks horrible compared to the 1200's, really yellowed and dirty, but the voltages of the pins looked spot on :) (plus it didn't have the high-pitched whine that the 1200's supply did when switched on.

The bad news is... the issue still remains.

So, as I see it, there are 2 options:

1. Ignore it for now - the keys do eventually work
2. Replace the CIA chips

I think eventually, assuming that the issue is (one of) the chips, then I would like to replace them.

So now the question is, does anyone know where I could get replacement chips and sockets? Is Ebay the best bet?

I'm hoping removing these chips may be made slightly easier to be removed by using kapton tape (to mask nearby components) and a hot air gun. I avoided using this method before, when replacing the capacitors, as I've heard they can explode, but a chip shouldn't be as dramatic, hopefully...

Thanks

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intric8
Seattle, WA, USA
Website

Posted Fri Sep 21, 2018 7:18 am

If I am right about the CIA chips going bad (which seems even more likely if your PSU was sending incorrect amps) one hypothesis is the keyboard will start working normally after they warm up. Like, your Amiga in her old age has started to turn into a VW Beetle! Just let it idle for two minutes before driving. Hah!

Congrats on figuring out the PSU. Those brick PSUs are one of the top killers of the C64/128 as those machines don't have cap issues for the most part. I'd def consider a new replacement if it fits your budget. (He can make products for the UK, too. He's a retired gentleman who won't be doing this type of work forever, if you know what I mean...)

The thing about CIA chips - on other Amigas they are socketed so if you get the odd/even mixed up it's easy to swap around and re-test. Converting to socketed sounds like a really smart plan if that's possible.

One last thing. Dumb thought but will put it out there.

I had my own A1200 open last night doing a bit of "what's in here again?" exploratory surgery before I sell it. During the process, I quickly rediscovered that the keyboard cable - that insanely short, fat green cable - could easily pop out of its home that attaches to the motherboard. There's that white rectangular retainer that's supposed to hold it in. I had to completely open the white retainer with needle nose, re-insert the green cable firmly and press the retainer back down to hold the thing in place. It's really kinda janky.

Assuming your cable looks good, I hope what the cable plugs into is OK. My money is on your CIA chips, though (at least one of them).

Good luck!





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