Intermittent floppy disk drive problems

[1024MAK]

The PSU can be tested with a digital multimeter, an oscilloscope and suitable test loads. The 9V DC output is a nominal voltage and not a fully regulated (stabilised) supply. The AC output just feeds from the transformer secondary winding.

Inside the QL, the +9V DC supply feeds the main 7805 voltage regulator, the output of which is a regulated (stabilised) +5V supply. This feeds all the digital circuitry. The +9V also supplies the Microdrives.

The nominal +9V should not drop below +7.5V including the low point of the ripple waveform at the full load current. If the voltage drops below +7.5V, the 7805 regulator will drop out of regulation and the +5V will fall. This may cause problems with the digital circuitry, including CPU, memory or I/O errors.

The AC output from the PSU is used to supply the two regulators that provide the +12V and -12V DC supplies. The +12V is used in the TV (UHF) / RGB / video section and the RS232 ports. The -12V is not important unless you are using the RS232 ports, and on some QLs, the Microdrives.

There are at least two designs of QL PSU. As far as I know, there is no visible difference on the outside. But internally the electrical design is different.

If you have a lab PSU, the QL can be fed with a regulated +7.5V to +9V on the +9V input and +15V to +16V on the AC input.

Mark

[georgeo]

Thanks again, Mark. Should I infer that the regulated +5V supply is fed to external interfaces such as the Trump card and in turn is used to signal the two floppy-disk drives connected to the Shugart interface?

It looks as if the (stepper?) motor that drives the read/write head is not being signalled to start. As it happens to either/ both drives, I'm assuming the motors are fine and that the signal to drive the motor is (sometimes) not getting through somewhere. Seeing as it is 'sometimes' and can be corrected by resetting the QL -- without touching or moving the ribbon cable -- I'm assuming its unlikely to be the ribbon cable.

Thanks again,
Georgeo.

[georgeo]

Well, the PSU has passed a basic test. The two feeds are reporting 15.5V AC and 10.5V DC, with good stability, when checked with a multimeter. The DC is a little high, though I suspect this is within the tolerance for the device.

Sadly, we were unable to test under load, but I think its reasonable to assume that the PSU is working correctly.

Next thing to check is the floppy-disk drive and ribbon cable ...

[Martin_Head]

Just a thought. Do you need to play with commands like FLP_START and FLP_STEP. It might be that the drives are working at the edge of compatibility with the Trump card.

[georgeo]

Hi everyone,

I have made some progress in that I've been unable to reproduce the problem with a different floppy-disk drive. I'll keep checking over the weekend, in case I've just been lucky so far. However, it suggests there may be a problem with my dual, floppy-disk unit or (floppy-disk drive) PSU.

The loan floppy disk unit that looks to work correctly has a single disk drive rather than a double drive. I take it that this shouldn't be a factor?

Thanks again,
Georgeo.

[tofro]

The loan floppy disk unit that looks to work correctly has a single disk drive rather than a double drive. I take it that this shouldn't be a factor?

Hmm. It could very well be the PSU of your dual floppy unit is at it's limit - Maybe it is designed to power a single unit only (Note even if you only use one drive at a time, the PSU needs to supply logic and motor current for both drives). You could open up the case and disconnect one of your dual drive's power supply cables - Then check again whether the remaining drive runs flawlessly.

Tobias

[georgeo]

Hi Tofro, Thanks. I wondered about this. I bought the drives and PSU as a package from SellMyRetro, so the PSU is spec'ed for the dual drives. However, the PSU might be faulty. I'll contact the seller, if the loan drive continues to be problem-free.

Thanks again,
Georgeo.

[1024MAK]

Most QL expansion cards use their own 7805 (or equivalent) voltage regulator powered from the +9V supply.

As said above, the PSU that supplies the disk drives must be rated to operate the motors in both disk drives at the same time. So at least 2A.

Mark

[georgeo]

Hi everyone,

I'm sad to report that a replacement PSU for my disk-drive unit doesn't solve the problem. I'm now unsure of the next step. I can see only two possibilities:

1. There is a problem inside the two-drive unit that is intermittently affecting both drives in the same way.
2. There is a problem with the Trump card that only appears when I have two floppy disk units connected.

Anyone else able to suggest something?

Thanks again,
Georgeo.

[robsoft]

Hi Georgeo. I'm going to be without my QL for a week or so, as I've sent if off for a check-up and recapping (along with some seriously poorly Spectrums, I thought I might as well send a joblot).

So, I could bundle up my Trump card clone (should be same as yours as we bought from the same seller) and my twin floppy drive & PSU - it's a little heavy because I put it all in an aluminium NAS-type external box but I could wrap this up securely and send it to you to try. I don't mind sending it one way, you'd probably have to pony-up to send it back afterwards though, which might be the wrong side of a fiver or so

That would give you a check on the card and the floppies - it's happily working here and even working both drives simultaneously has been fine (copying from flp1_ to flp2_ etc etc). You could test your card with my floppies, and my card with your floppies. Just promise me you won't mix them up when you send them back

I'm not going to be able to post it for a day or two because I'm not at home much this week but if you PM me your details (or email to 'my first name' at robsoft dot net) we can sort something out. I should be able to send it to you before the weekend.

Have a think about it, the offer is there anyway