DDI-1 Interface Fault

[simondo]

Hi,

I have  aquired a spare DDI-1 interface but it will not read a disk on a known good FD-1, Retry, Ignore, Cancel. My other DDI-1 interface works fine.
Amsdos commands can be accessed on the faulty DDi-1
Continuity check of floppy cable frpm DDI-1 to floppy connector ok. Service manual doesn't help.
Any help would be much appreciated.

[eto]

Just to be sure: It's connected to a 464? The drive is in both cases connected to the same connector and would always be drive A?

[simondo]

Apologies if I was not as clear as I could have been.
Its a CPC464 and DDI-1 and DDI-1  floppy drive.

I have a working DDI-1 interface and working DDI-1 floppy drive as drive A. (I referred to it as FD-1 in my post above, but it says DDI-1 on label).

I have acquired another DDI-1 interface and tested it by connecting it to my working DDI-1 floppy drive as drive A in the same way as above  but get retry  ignore cancel. Therefore this 'new' interface is not working. The floppy drive is attempting to read disk.

Hope this makes sense.

[Audronic]

@simondo 

Can you tell me the Whole Message that is on the screen when it fails.

Thanks

Keep Safe

Ray

[Bryce]

Apologies if I was not as clear as I could have been.
Its a CPC464 and DDI-1 and DDI-1  floppy drive.

I have a working DDI-1 interface and working DDI-1 floppy drive as drive A. (I referred to it as FD-1 in my post above, but it says DDI-1 on label).

I have acquired another DDI-1 interface and tested it by connecting it to my working DDI-1 floppy drive as drive A in the same way as above  but get retry  ignore cancel. Therefore this 'new' interface is not working. The floppy drive is attempting to read disk.

Hope this makes sense.

This is almost always down to two possible issues:
1 - Bad contact to the expansion port. Cleaning the contacts of the DDI-1 would solve this.
2 - One of the buffer IC's in the expansion has failed. These are the two 74LS38 chips right beside the flat cable. 

Bryce.

[simondo]

Bryce,

Many thanks for your help as always. 
First thing I did was clean CPC edge connector and DDI contacts.
I am going to check the 74LS38 chips you mentioned by comparing voltages and waveforms at the pins on both the working DDI-1 and the faulty DDI-1 and possibly change them out. I don't have a desoldering station and wary about lifting pads, although I may give it a go with some low melt leaded solder.

Thanks.

[simondo]

@simondo

Can you tell me the Whole Message that is on the screen when it fails.

Thanks

Keep Safe

Ray

Ray,

whole message:
Drive A: Disk Missing
Retry, Ignore or Cancel

[Bryce]

Bryce,

Many thanks for your help as always.
First thing I did was clean CPC edge connector and DDI contacts.
I am going to check the 74LS38 chips you mentioned by comparing voltages and waveforms at the pins on both the working DDI-1 and the faulty DDI-1 and possibly change them out. I don't have a desoldering station and wary about lifting pads, although I may give it a go with some low melt leaded solder.

Thanks.

Use this method: https://www.cpcwiki.eu/index.php/IC_Repair
The chips are already very close to the flat cable connector which makes removal (in one piece) quite difficult even if you had a de-soldering station.

Bryce.

[Audronic]

@simondo

Can you tell me the Whole Message that is on the screen when it fails.

Ray,

whole message:
Drive A: Disk Missing
Retry, Ignore or Cancel

This message for me indicates that the INDEX pulse is not being read by the controller or the disk is NOT spinning ??.

Keep Safe

Ray 

[simondo]

@simondo

Can you tell me the Whole Message that is on the screen when it fails.

Ray,

whole message:
Drive A: Disk Missing
Retry, Ignore or Cancel

This message for me indicates that the INDEX pulse is not being read by the controller or the disk is NOT spinning ??.

Keep Safe

Ray

Disk is spinning and attempting to to read disk if that helps.
Simon

[Bryce]

Then check pin 17 of the FDC to see if the Index signal is getting back. If not check pin 4 of the 74LS240 to see if that chip has failed. If pin 4 isn't getting an index pulse, then the problem is in the flat cable.

Bryce.

[simondo]

Then check pin 17 of the FDC to see if the Index signal is getting back. If not check pin 4 of the 74LS240 to see if that chip has failed. If pin 4 isn't getting an index pulse, then the problem is in the flat cable.

Bryce.

Bryce,

Many thanks.

I'm back at work next week after being off for a while where I have a better o'scope, multimeter and soldering iron than at home. I can then do all the checks you've suggested and keep you all updated.

Regards,

Simon