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Microdrive spinning ad infinitum...

Posted: Tue Oct 08, 2019 6:19 pm
by af0l
I've always been a big fan of the QL, it just seemed such a posh machine to me... But i only recently acquired one, which was in somewhat battered state, lacking a PSU, shredded membrane, you name it.

I've managed to fix it up, install a PicoPSU and bring it to life. In the process I fried the bus transceiver by reversing polarity on the 5V rail... But that's fixed now, yet there is an issue that remains. Sometimes the microdrives act normally as far as I can gather. After picking the monitor or TV the drive 1 light is lit and the motor spins for a couple of seconds, then stops. But that's rarely. Most of the time the drive just keeps spinning and nothing except a reset gets it out of the loop. The keyboard remains unresponsive. This happens with both drives, I can swap them and still get the same result, so I'm thinking it's not the microdrive or those nasty cables.

Any Idea where I might start looking?

Re: Microdrive spinning ad infinitum...

Posted: Tue Oct 08, 2019 6:25 pm
by mk79
LDie ist [url][/url]

Re: Microdrive spinning ad infinitum...

Posted: Tue Oct 08, 2019 6:56 pm
by af0l
mk79 wrote:LDie ist [url][/url]


Yes, yes, 45il od&h :D

Re: Microdrive spinning ad infinitum...

Posted: Tue Oct 08, 2019 7:47 pm
by mk79
Wow, that text was actually typed by my phone without my knowledge while being unlocked in my pocket. I was only notified of it because you quoted me :D Interesting. Sorry I don't have any further ideas regarding your problem (and apparently Siri doesn't have any either).

Re: Microdrive spinning ad infinitum...

Posted: Tue Oct 08, 2019 9:38 pm
by af0l
Hehe, thank you and Siri for your effort anyway...

Re: Microdrive spinning ad infinitum...

Posted: Tue Oct 08, 2019 10:19 pm
by Nasta
Check that the 8302 ULA is well and alive. This sounds like either an interrupt is left 'hanging' or the MDV select signal or some other logic is - in either case, it's the 8302 that generates those control signals. Reversing the 5V polarity is REALLY dangerous and can easily damage any chip in the QL - perhaps not to the point of outright failure (the one that fails first will likely save the others as it will short the offending reversed supply making it go to a very low voltage) but you may get 99% operational chips. And, if you know anything about computers, they all rely on chips being 100.00000% operational :)

Re: Microdrive spinning ad infinitum...

Posted: Wed Oct 09, 2019 8:32 am
by af0l
Thanks, I know the polarity is not to be reversed, yet I did it anyway :)

I got similar advice on FB, I even desoldered the socket for 8302 as it looked dodgy, + the resistor mod was done in a way, that the chip wouldn't sit down properly... Replaced the 8302 with a new one, the problem still persists.

I went on and desoldered and tested all the relevant transistors. No luck so far...

Re: Microdrive spinning ad infinitum...

Posted: Wed Oct 09, 2019 8:37 am
by vanpeebles
Is a pico suitable for powering the microdrives? I thought when running at 5v with a none standard PSU, you loose the microdrives? :)

Re: Microdrive spinning ad infinitum...

Posted: Wed Oct 09, 2019 11:15 am
by martyn_hill
Hi!

VP makes a good point that I hadn't considered.

Have you configured the picoUSB to drive 9V in to the respective Vin connector on the motherboard, or instead 5V directly in to where the output from the main 5V linear regulator feeds the board?

If the former, then aside from any residual damage from the earlier power reversal, we might otherwise expect the MDVs to work.

If the later, then both the MDV ULA and the Motor (and Erase current) would be without a power supply at all, as both rely on the 9V rail to feed them (the ULA via its own onboard 5V reg.)

No doubt you've considered all this already, but thought to chip-in none-the-less.

Good luck!

Re: Microdrive spinning ad infinitum...

Posted: Wed Oct 09, 2019 3:06 pm
by af0l
Thanks for all your input, guys. Yes I did have to add a TracoPower TSR 2-2490 to the mix. I found an injection point for 9V elsewhere on the board, since I made myself a nifty 3d printed stand for the QL fryer...

So yes, it is powered I can measure the 9V on the regulator leg of the MDV.

I'm now making a cable with turned pin headers to replace the original/make sure the contact is good. I'm going to pull them in and out a lot anyway, or so it seems...