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Old 28 June 2020, 16:45   #1
bwldrbst
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Possible CIA problem

I've been trying to diagnose an issue with my A2000.

The external floppy port doesn't seem to work at all - a drive connected to it does not do anything. No sound, no flash of the LED. It doesn't seem to be getting power. The drive works fine on another Amiga.

Also, the parallel port does not work correctly. I've been trying to get a plipbox working with it. The plipbox detects when I try to bring it online but the TCP stack is unable to acquire an IP address. Trying to send a packet from the plipbox to the Amiga gives an error. The plipbox also works fine on another machine.

I've tried exchanging both CIAs with spares that I believe are good but there was no change in behaviour.

Where should I look next?

Cheers,

Andrew
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Old 28 June 2020, 17:18   #2
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Have you verified that the power rails are getting to the port pins? And that they are within acceptable range?
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Old 29 June 2020, 01:53   #3
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Originally Posted by solarmon View Post
Have you verified that the power rails are getting to the port pins? And that they are within acceptable range?
That's going to be the next thing I check.
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Old 02 July 2020, 17:01   #4
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I've measured the voltage at the PSU motherboard connector with a floppy drive, scsi2sd and cdrom connected. 5V lines register ~4.9 volts, +12V reads as 11.6 and -12V reads as -11.3.

Are these reasonable or is it meaningless without more load?

I also measured the 5V and 12V, pins 12 and 23, of the external floppy connector. 12V was 11.6 but there was nothing on the 5V pin. I guess that explains the external floppy not working.

Having a look at the schematic, it seems I should be able to measure connectivity between that pin and EMI321 but there's none. Cracked solder join perhaps?

I measured pin 14 of the parallel port and it showed 4.8V or so. Maybe one of the other pins is suffering the same problem?

Pin 12 should be connected to EMI337 and 13 to EMI338 but there's no connectivity. Could be my problem?

A spare parts motherboard I have shows connectivity on all those pins to the EMIxxx components.

Does this sound like reasonable troubleshooting? My plan now is to pull the motherboard out of the chassis and reflow the solder on those pins.

Any other suggestions?
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Old 02 July 2020, 19:06   #5
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Measuring the voltages with the motherboard powered should be good enough.

Anywhere where you expect continuity and it does have it is an obvious issue that needs to be resolved. So you are going about this the right way.

If there are any signs of corrosion or oxidation it needs to be cleaned up. Yes, I would reflow the pins of the connectors, and I would check the pins and traces carefully with a USB microscope.
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Old 04 July 2020, 09:55   #6
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There was a clear break in the trace between pin 12 of the floppy port and EMI321. Repaired that and the external floppy drive works again. Great!

I re-tested the parallel port pins and they all appear to have connectivity to their nearest neighbour. Next I'm going to make sure they all reach the CIAs.
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Old 04 July 2020, 12:33   #7
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Great! Well done for fixing it!

It might be worth making a parallel loopback adapter and use Amiga Test Kit to perform a parallel loopback test.
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Old 05 July 2020, 06:34   #8
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It might be worth making a parallel loopback adapter and use Amiga Test Kit to perform a parallel loopback test.
Good idea, I'm going to do that today.

Naturally, I've damaged the hook clip for my 2MB Agnus adaptor while getting the PSU/Drive Bay assembly in and out so many times
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Old 05 July 2020, 10:29   #9
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Well, that hasn't helped much. Amiga Test Kit reports all pins of the parallel port as working.

It's memory test did pick up an issue with Chip RAM though.
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