Disk Interface Diagram

[belg4rion67]

Hi to all, if are not copyright protected, is possible to have form somebody the wiring diagrams of most known floppy disk interfaces for rebuilt/repair ?
I'm an electronic engineer with passion of built/rebuilt old circuit boards, all helps from you are well accepted
Ciao!!1

[Mr_Navigator]

Hi, elg4rion67 a recent circuit diagram appeared on the mailing list of the MEDIC disc interface, here http://tfs.firshman.co.uk/temp/medic.zip, I also have the circuit board but it is not working at the moment, I also have the Microperipheral's disc interface that also doesn't work properly, if you are able to help that would be great. I have high res pictures of these here, you may be able to get circuit diagrams from here https://sites.google.com/site/theqlimag ... y/products

[prime]

Humm I notice that the MicroPheripherals interface uses a WD2793, depending on what it does when connected to the QL it may be that the variable cap / variable resistor that adjust the timing of this chip need adjusting. The procedure for doing this is outlined in the WD279x datasheet, but you will need a scope to do this

What I do find odd however is that there is only one variable resistor, designs using the WD279x typically have 2, one for adjusting the write pulse and one of adjusting the read pulse.

Of course if the board is not allowing the QL to boot or something like that, then this may not be the case. If you can boot with drives atached what happens if you try and access / format them do the drives select and spin up but fail to read / write ?

Cheers.

Phill.

[Mr_Navigator]

Firstly I can boot with either interfaces plugged in on their own, however with a memory expansion card the QL will not boot and I get a white screen. On their own, one boots up and I can DIR or FORMAT command to the disc, however I get a time-out error, the other I get no disc recognition at all. Someone suggested that the WD2793 may be faulty, however I have searched the web for new WD2793, found one American company quoted me a minimum of 4 for $200 which is a bit steep on a hunch. Also if you are going by the CCT pictures then you are looking at the one with the DIP switches, whereas the other interface is a slightly different design with no DIP switches but with the two variable resistors as you describe. The data-sheet I read refers only to 5 1/4 and 8 inch disk drives, not 3.5, would that mean they are incompatible with 3.5 inch drives or it was just they weren't out yet?

Have just taken more photos of the second Microperipherals Floppy Disk Interface Card Number 2 and noticed another different aspect, with the case removed I found 5 pairs of jumper pins see here https://picasaweb.google.com/lee.privet ... 3798649394

[prime]

I would agree that it's possibly the WD2793 that's gone in one board, you could of course try swapping the one from the other board and see if you get any response.

Also when you say no reponse do you mean literally nothing ? no drive lights come on and the drive motors don't spin ? Typically these functions are controlled by a seperate latch register which is written to independently of the disk control chip. Typically this would be something like a 74LS373, or a similar latch chip, you should be able to determine this by tracing the drive select / motor on lines from the floppy connector.

The Dragon 32/64 DragonDos controlers use the WD2797, and have used this with 3.5" drives without any problem, also the RM Nimbus uses the very same WD2793, with 3.5" drives and works. I guess 3.5" drives where not out when the datasheet was written. I have found for the most part with correctly designed hardware that 3.5" drives and 5.25" can be used interchangably.

Apparently BGMicro have them : http://www.bgmicro.com/ICS2793.aspx but might be woth contacting them and checking if it does turn out to be a faulty WD2793.

Cheers.

Phill.

[Mr_Navigator]

Yep, site looks promising will look at that, at a later time in detail.

Also will go through whole procedure and duplicate for each interface card and note the conditions of lights etc. (and then I will tell you about the Medic card I have also that doesn't work) .Thanks

[belg4rion67]

Many thanks to all Mr Navigator for useful infos: in effect I've tried also to find the WD ic's and the only seller is an american site but price is higher for a so older chip!!
I think that I'll try to find someone that sell me a disk interface....
Best regards guys
Ciao!