Microdrive constantly running

[The-Red-Bayron]

Hi, I am new to the QL and this forum. I have recently got a QL and luckily it was fully working. Unfortunately the last time that I re assembled it the TR6 (ZTX 551) transistor bent and possibly shorted, I have taken the TR6 out and the TR4 (BC184) and they are both checking out electrically. When you power up the QL it gets to the screen choice (F1 F2) then starts the motor on the Microdrive, the screen remains blue but the flashing red cursor never appears the motor just runs. If I remove the Microdrive it will boot into basic. I am thinking that the 2G007 ULA is damaged but wondered if the were other test that I could do before trying to get a replacement. Any tips would be greatly appreciated.

[dilwyn]

There is a QL Service Manual available online which might have information to help you:
https://www.sinclairql.net/srv/index.html

or somewhere on this page:
https://dilwyn.qlforum.co.uk/docs/manuals/index.html

[tofro]

First thing I'd do is to swap drive 1 and 2 - That allows you to identify whether your problem is on the mdv headboard or the QL side (the transistors). If drive 2 in drive 1's place stops properly, that clearly points towards the drive 1 headboard, thus the mdv1 ULA (the QL starting up normally without any drive connected, that's a strong hint towards that, but not a proof.)

[The-Red-Bayron]

Hi Dilwyn, thanks for the info I have downloaded the manual, also the manual for the vMap as this gives a description of the startup for the different drives.

Hi Tofro, thanks for the suggestion I have tried swapping the drives over and MDV2 does the the same thing with the motor running all the time, so hopefully it is a transistor problem more than a ULA problem. I have ordered replacements for TR 5, and TR 6,7 so fingers crossed this will fix it. I'll continue the post once the parts arrive. Fingers crossed it will be good news.

Thanks again to the both of you for your help.

[The-Red-Bayron]

Hi Dilwyn and Tofro,

Problem solved!! QL and both Microdrives working again!! One of the pieces of advice that I got (before I posted this message) was to replace all the Electrolytic Capacitors and the Voltage Regulators with modern equivalents. I have done this on some ZX Spectrums with no problems and good working results. The problem that I got with the QL Microdrives was the new Regulators, I saw some info from a ZX Spectrum site (Byte Delight) that covered Microdrive faults (https://www.bytedelight.com/?page_id=1623) "When a Microdrive keeps spinning and the ZX Spectrum doesn’t respond anymore. Replace the 7805 of the Microdrive". So I put the original Regulators back in and everything worked.

It took a few days to confirm this as the replacement Transistors were delayed in the post so I couldn't check the motor circuit until they had arrived.

Thanks for your help with this so glad that it was not something more serious.

[The-Red-Bayron]

Just an update on this, everything was working fine then BOOM!! When I plugged in the QL flash bang!!

I checked the PSU all OK. The bang had come from the main board and when I investigated the L5 inductor had blown, located next to the reset switch. This is the main 9v supply rail to the microdrives.

Tested each drive with a bench power supply with the current limiter set to 200 ma, MDV2 was tripping out. After a bit of fault finding the cause was that the input smoothing capacitor had gone short circuit causing the L5 to blow like a fuse.

A good place for microdrive info is from Ben of "Byte Delight", here is a link: https://www.bytedelight.com/?page_id=1623 he recommends to replace all the smoothing capacitors with 1uf, this is a bit of a squeeze with electrolytic caps but they just fit. Anyway the main thing is that both drives are working again.