AKF12 display issues

Arc/RPCs, peripherals, RISCOS operating system & ARM kit eg GP2x, BeagleBoard
philb
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Joined: Sat Aug 05, 2017 6:05 pm

AKF12 display issues

Postby philb » Sun Oct 01, 2017 6:46 pm

Today I replaced the PSU caps and battery in my A3000 and tried powering it up for the first time in quite a while. It boots as far as the desktop which is somewhat encouraging. But there are a couple of things wrong with it:

1. The right-hand side of the keyboard doesn't work properly, and the power LED only lights very dimly. I suspect there is probably some track damage on the main PCB from battery leakage and I expect this should be fairly straightforward to sort out.

2. Using my old AKF12, which is the only monitor that I have an appropriate cable on hand for, the colours are a little bit messed up and the display is bouncing up and down. I am assuming that the latter of these, at least, is probably a fault in the monitor rather than the computer. Dried up electrolytics again causing unstable supply rails? Are there any particular AKF12 failure points that I ought to be looking for?

I also finished re-capping one of my BBC PSUs, four to go. Bit of a tedious business that!

RobC
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Re: AKF12 display issues

Postby RobC » Sun Oct 01, 2017 7:51 pm

philb wrote:1. The right-hand side of the keyboard doesn't work properly, and the power LED only lights very dimly. I suspect there is probably some track damage on the main PCB from battery leakage and I expect this should be fairly straightforward to sort out.

This could be track damage but might also be caused by damage to the keyboard membrane which can be repaired with silver conductive paint.

philb
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Re: AKF12 display issues

Postby philb » Sun Oct 08, 2017 1:20 pm

I'm pleased to report that replacing the four big electrolytic caps on the AKF12 power supply board seems to have cured the display issues and the picture now looks pretty good.

Here's the PCB in question. It comes out of the monitor easily, no need to remove the chassis or mess with any of the connections to the tube.

Image

I took the A3000 keyboard apart and cleaned up the membrane a bit which has got most of the keys working. I now seem to be missing just one column, the one that goes down through "D". Need to trace the circuit a bit to figure out which pin on the connector that corresponds to.

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DutchAcorn
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Re: AKF12 display issues

Postby DutchAcorn » Sun Oct 08, 2017 1:29 pm

philb wrote:...I took the A3000 keyboard apart and cleaned up the membrane a bit which has got most of the keys working. I now seem to be missing just one column, the one that goes down through "D". Need to trace the circuit a bit to figure out which pin on the connector that corresponds to.


Tom posted a mapping between the keys on the keyboard and the pins on the keyboard connector in this post.
Paul

philb
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Re: AKF12 display issues

Postby philb » Sun Oct 08, 2017 2:09 pm

Oh right, perfect. So it looks as though the "yellow column" on pin5 is my problem.

I also seem to still have some sort of CMOS RAM difficulties since the machine only boots to the Supervisor prompt today (although last week it was happily starting the desktop) and delete-power-on doesn't seem to help. It'll be easier to debug that once I can type things like *DESKTOP :-)

philb
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Re: AKF12 display issues

Postby philb » Sat Oct 14, 2017 4:36 pm

I soldered a wire to reconnect SK7 pin 5 to IC4 (having belatedly realised that both these parts are through-hole so soldering them on the back is much easier than doing it on the front!) and that does seem to have fixed my missing yellow column. I'm still missing ctrl and left shift which suggests the cyan column is also broken, though slightly strangely I think right shift and Break were working OK. Might have to have another look inside the keyboard I suppose.

I also haven't quite figured out what's wrong with the keyboard LEDs. I did a continuity check between the SK7 pin and main +5V and it seems fine. Might be a bad track on the flex circuit itself maybe.

Also discovered that the machine does start the desktop fine if I type *DESKTOP but it always stops at the Supervisor prompt after a reset. Is this likely to be bad CMOS?

RobC
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Re: AKF12 display issues

Postby RobC » Sat Oct 14, 2017 5:03 pm

philb wrote:Also discovered that the machine does start the desktop fine if I type *DESKTOP but it always stops at the Supervisor prompt after a reset. Is this likely to be bad CMOS?

Could be. What does *STATUS give for the "Language" setting? I think it should be 10 for the desktop.

philb
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Joined: Sat Aug 05, 2017 6:05 pm

Re: AKF12 display issues

Postby philb » Sat Oct 14, 2017 5:20 pm

Thanks. it was set to 2. I changed it to some other random number and it did seem to remember it over a power cycle.

I'll try configuring it to 10 and see what happens, though I'm a bit puzzled that delete-power-on didn't put it back to the right value at least transiently.


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