Disc Missing and Bad Command

[eto]

I have a CPC 6128 here where I got the infamous "Disc Missing" and then the "Bad Command" symptoms.

Floppy could be ruled out as it also happens with a known working GOTEK.

When I switch to drive B (another GOTEK) the whole system hangs and after a soft reset the boot process stops before the "BASIC 1.1" message until I turn it off.

I already replaced almost everything related to the FDC part of the motherboard: AMSDOS, u765, all LS-ICs (with the IC numbers 2xx). The only ICs that have not been replaced are the 74HC161 and the FD9216 data separator (as I don't have replacements for them here).

Weirdly enough now the logon message is no longer "Schneider" but "ISP". This makes me wonder if something completely different is the actual culprit...

any idea? The firmware maybe?


EDIT: I can enter commands and even BASIC but when the cursor crosses the screen border it simply vanishes without scrolling. BASIC seems to stop working as command have no effect any longer. The only thing that still works is a soft reset.

[Brocky]

id say the floppy issues is something to do with your cable...i remember them symptoms from when i setup a 3.5in drive and it was a wrong pin used on the cable..

as for the schneider vs isp... it seems the pins of the PIO to the "LK" links isnt connected right... ISP is 0,0,0 on the 3 links (LK1, LK2, LK3)...schenider is set to 1,0,1

the issue under ya edit is a totally new one to me!..never seen that!

[Rabs]

I have a CPC 6128 here where I got the infamous "Disc Missing" and then the "Bad Command" symptoms.

Floppy could be ruled out as it also happens with a known working GOTEK.

When I switch to drive B (another GOTEK) the whole system hangs and after a soft reset the boot process stops before the "BASIC 1.1" message until I turn it off.

I already replaced almost everything related to the FDC part of the motherboard: AMSDOS, u765, all LS-ICs (with the IC numbers 2xx). The only ICs that have not been replaced are the 74HC161 and the FD9216 data separator (as I don't have replacements for them here).

Weirdly enough now the logon message is no longer "Schneider" but "ISP". This makes me wonder if something completely different is the actual culprit...

any idea? The firmware maybe?


EDIT: I can enter commands and even BASIC but when the cursor crosses the screen border it simply vanishes without scrolling. BASIC seems to stop working as command have no effect any longer. The only thing that still works is a soft reset.

I had a 664, a while back, which resulted in a hang before the BASIC prompt. This was related to ROMDIS problems and a broken track on the disc controller side of the PCB. Not saying this is your problem but may give you some ideas. Appears your problem has more subtle symptoms.

In my case,

IC205 PIN 2 AND gate input was floating high, should have been held low by IC212 PIN 5.
IC205 PIN 1 AND gate input is connected to A15
IC203 PIN 3 AND gate output is connected to ROMDIS

Every time A15 went high, the ROM was disabled and hence the hang before BASIC.

Hope this helps, Rabs.

[eto]

id say the floppy issues is something to do with your cable...i remember them symptoms from when i setup a 3.5in drive and it was a wrong pin used on the cable..

I resoldered all pins and it also happens on Drive B if Drive A is not connected.

it seems the pins of the PIO to the "LK" links isnt connected right

They are set to "Schneider". That's why I think it is relevant in this case. As I get into BASIC, can execute commands but Floppy access is not possible, scrolling does not work and the system thinks it gets the wrong value from the LK links, I got the feeling that there is something involved which is not a typical cause of the "Bad command" problem. 

[eto]

Not saying this is your problem but may give you some ideas.

I'll have a look at that signal. Thanks

[Audronic]

Perhaps the port thinks it has all Zero's on the 4 Pins ??

LK1,LK2,LK3
LK1,LK2,LK3 are optional links on the CPC mainboard, connected to PPI Port B, Bit1-3. The links select the distributor name (which is displayed by the BIOS in the boot message).
These LKs exist on all CPC mainboards. By default, LK1-LK3 are not installed (Amstrad). Other combinations are LK2 installed in german Schneider models, and LK1+LK2 in australian Awa models.

Bit 3 (LK3)	Bit 2 (LK2)	Bit 1 (LK1)	Distributor Name	Usage
0 (link installed)	0 (link installed)	0 (link installed)	Isp	None
0 (link installed)	0 (link installed)	1 (no link)	Triumph	None
0 (link installed)	1 (no link)	0 (link installed)	Saisho	None
0 (link installed)	1 (no link)	1 (no link)	Solavox	See below
1 (no link)	0 (link installed)	0 (link installed)	Awa	Australian CPCs
1 (no link)	0 (link installed)	1 (no link)	Schneider	German CPCs until late 1987
1 (no link)	1 (no link)	0 (link installed)	Orion	None
1 (no link)	1 (no link)	1 (no link)	Amstrad	Default, used in most countries

[eto]

Perhaps the port thinks it has all Zero's on the 4 Pins ??

Not really sure if that's the case. I expect that there is a common underyling problem of the 3 symptoms: 

1) boot message is ISP (all 0 although there should be one 1)
2) when scrolling should happen the system hangs
3) bad command

I have the impression there is something wrong when writing/reading I/O ports. But it can't be the usual suspects as the computer boots normally and RAM/ROM tests worked well. 

[Rabs]

1) boot message is ISP (all 0 although there should be one 1)

I remember watching a disk controller investigation by Noel that displayed ISP, see Floppy Disk Controller Repair.

This turned out to be the IC203 and I have had problems with this IC in the past, see my posts CPC 6128 DISC MISSING BUT THE DISC DRIVE IS GOOD

But I guess you may have already replaced IC203 and checked all the tracks?

Hope this helps
Rabs

[eto]

I remember watching a disk controller investigation by Noel that displayed ISP, see Floppy Disk Controller Repair.

oh... this is very close to what I experience. Thanks for bringing it up. 

[eto]

checked all the tracks?

seems I cracked one track  from IC203 to IC210  while replacing the ICs. I couldn't find the actual crack but there was no connection any more. 

I'm now back at "disc missing" followed by "bad command". 

So far all other tracks seem to be fine and I replaced all ICs except for two which I need to order first.