CPC 6128 returns "Bad command" on cat

Started by konc, 10:36, 16 March 22

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vasilisk

#25
I have the same symptoms as konc (bad command on cat). I checked the voltages and I have 5,176 in the powerjack when cpc is off and 4,873 when cpc is on. I dont have 1.1 drop like konc but a small one. I dont know if this is enough for the same symptoms.
I also checked the voltages that go to the drive itself. i have 12.1 and 4.81. Is 4.81 enough? Should it be at least 5?

konc

#26
Quoting myself

Quote from: konc on 11:57, 22 March 22Brought a friend over with a proper bench PSU, the same. We increased temporarily the voltage to 5.6V so that the Amstrad gets 4.5V (again the same 1.1V drop) and everything is working correctly. I loaded and played 2 games!

So even 4.5 is enough. 4.8-4.9 are very common values and considered normal


vasilisk

So back to square one for me. I have to find (with some help) which chip might be failing

tjohnson

Is the drive doing anything when you type cat, does it spin up?

eto

If I am not mistaken, "Bad Command" can also happen if the head is not moving.

vasilisk

Quote from: eto on 12:47, 30 April 22If I am not mistaken, "Bad Command" can also happen if the head is not moving.
That is correct. The head is not moving. I have to find why. Because i dont want to hijack konc's thread, I have already started a similar topic a couple of months ago. I am here because the voltages was a new undiscovered approach. 

Bryce

A quick lesson in drive failure diagnosis:

The first thing that "Bad command" tells you is that BASIC hasn't registered the commands that ROM7 offers. The next step is to find out why. Does ROM7 work? Is it getting the voltage required? (probably, because the rest of the computer works). Is it damaged? Can you get ROM7 to react to anything? What gets sent to the 765 when you do a CAT and how does it react to the command?
The head will only move if everything works: ie: ROM7 understood the command and sent it to the disk controller (765). So the next step is to check whether the ROM correctly reacted to the command. If it did, then the next step is to check what the 765 did after the command arrived: Did it activate the correct outputs? If it did, you need to look at how the drive reacted to those outputs. Were all the bits (drive select, MotorOn, Step, etc) set correctly (there are several buffers IC's in between that could have failed)? If they were, why didn't the drive react accordingly? Broken connection, failed buffer? Is the 12V rail missing? Is the drive spinning up? Is the 765 getting a proper index pulse back from the drive?

Start from the source and work towards the mechanical results. Check that all the right signals are getting sent (CPU -> ROM7 -> 765 -> Buffers -> Drive). Then check that the drive has the voltages to react to them and then check that the drive is sending the right signals back (also via buffer IC's).

Bryce.

vasilisk

Quote from: Bryce on 19:33, 30 April 22A quick lesson in drive failure diagnosis:

The first thing that "Bad command" tells you is that BASIC hasn't registered the commands that ROM7 offers. The next step is to find out why. Does ROM7 work? Is it getting the voltage required? (probably, because the rest of the computer works). Is it damaged? Can you get ROM7 to react to anything? What gets sent to the 765 when you do a CAT and how does it react to the command?
The head will only move if everything works: ie: ROM7 understood the command and sent it to the disk controller (765). So the next step is to check whether the ROM correctly reacted to the command. If it did, then the next step is to check what the 765 did after the command arrived: Did it activate the correct outputs? If it did, you need to look at how the drive reacted to those outputs. Were all the bits (drive select, MotorOn, Step, etc) set correctly (there are several buffers IC's in between that could have failed)? If they were, why didn't the drive react accordingly? Broken connection, failed buffer? Is the 12V rail missing? Is the drive spinning up? Is the 765 getting a proper index pulse back from the drive?

Start from the source and work towards the mechanical results. Check that all the right signals are getting sent (CPU -> ROM7 -> 765 -> Buffers -> Drive). Then check that the drive has the voltages to react to them and then check that the drive is sending the right signals back (also via buffer IC's).

Bryce.
The only thing that is tested and work, is the drive itself (Connected in another cpc6128). The other links in the chain I dont have the knowledge and the ability to test them.

Bryce

Quote from: vasilisk on 19:56, 30 April 22
Quote from: Bryce on 19:33, 30 April 22A quick lesson in drive failure diagnosis:

The first thing that "Bad command" tells you is that BASIC hasn't registered the commands that ROM7 offers. The next step is to find out why. Does ROM7 work? Is it getting the voltage required? (probably, because the rest of the computer works). Is it damaged? Can you get ROM7 to react to anything? What gets sent to the 765 when you do a CAT and how does it react to the command?
The head will only move if everything works: ie: ROM7 understood the command and sent it to the disk controller (765). So the next step is to check whether the ROM correctly reacted to the command. If it did, then the next step is to check what the 765 did after the command arrived: Did it activate the correct outputs? If it did, you need to look at how the drive reacted to those outputs. Were all the bits (drive select, MotorOn, Step, etc) set correctly (there are several buffers IC's in between that could have failed)? If they were, why didn't the drive react accordingly? Broken connection, failed buffer? Is the 12V rail missing? Is the drive spinning up? Is the 765 getting a proper index pulse back from the drive?

Start from the source and work towards the mechanical results. Check that all the right signals are getting sent (CPU -> ROM7 -> 765 -> Buffers -> Drive). Then check that the drive has the voltages to react to them and then check that the drive is sending the right signals back (also via buffer IC's).

Bryce.
The only thing that is tested and work, is the drive itself (Connected in another cpc6128). The other links in the chain I dont have the knowledge and the ability to test them.
Then you need to send your mainboard to someone who can check the first parts of the chain.

Bryce.

vasilisk

Quote from: Bryce on 20:04, 30 April 22
Quote from: vasilisk on 19:56, 30 April 22
Quote from: Bryce on 19:33, 30 April 22A quick lesson in drive failure diagnosis:

The first thing that "Bad command" tells you is that BASIC hasn't registered the commands that ROM7 offers. The next step is to find out why. Does ROM7 work? Is it getting the voltage required? (probably, because the rest of the computer works). Is it damaged? Can you get ROM7 to react to anything? What gets sent to the 765 when you do a CAT and how does it react to the command?
The head will only move if everything works: ie: ROM7 understood the command and sent it to the disk controller (765). So the next step is to check whether the ROM correctly reacted to the command. If it did, then the next step is to check what the 765 did after the command arrived: Did it activate the correct outputs? If it did, you need to look at how the drive reacted to those outputs. Were all the bits (drive select, MotorOn, Step, etc) set correctly (there are several buffers IC's in between that could have failed)? If they were, why didn't the drive react accordingly? Broken connection, failed buffer? Is the 12V rail missing? Is the drive spinning up? Is the 765 getting a proper index pulse back from the drive?

Start from the source and work towards the mechanical results. Check that all the right signals are getting sent (CPU -> ROM7 -> 765 -> Buffers -> Drive). Then check that the drive has the voltages to react to them and then check that the drive is sending the right signals back (also via buffer IC's).

Bryce.
The only thing that is tested and work, is the drive itself (Connected in another cpc6128). The other links in the chain I dont have the knowledge and the ability to test them.
Then you need to send your mainboard to someone who can check the first parts of the chain.

Bryce.
I was about to. I waited to check the voltages like konc's situtation

dragon

#35
Quote from: konc on 16:10, 14 April 22Behold a fully socketed board that's driving me nuts.

I removed every single chip to power on the computer without it and check the voltage, none made any difference. Still the same 1.1V drop, so no chip is shorted or makes a bad connection.

Unless anyone has a new hunch I don't see what else I can do with it except keeping it for parts (especially now that I can remove any chip easily!) and placing a local ad for a new one.



Have you check the tape relay?. It's connected to the 5v power line when you take out all ics In socket.

Bryce

Are you sure you've properly cleaned the power switch and power socket?

Bryce.

konc

#37
Quote from: dragon on 14:34, 24 May 22
Quote from: konc on 16:10, 14 April 22Behold a fully socketed board that's driving me nuts.
I removed every single chip to power on the computer without it and check the voltage, none made any difference. Still the same 1.1V drop, so no chip is shorted or makes a bad connection.
Unless anyone has a new hunch I don't see what else I can do with it except keeping it for parts (especially now that I can remove any chip easily!) and placing a local ad for a new one.

Have you check the tape relay?. It's connected to the 5v power line when you take out all ics In socket.

That's the Omron black or white box on the top left of the motherboard, right? I removed it completely and measured, no change.
When I say I tried removing every IC I mean one by one, removing the IC, soldering a socket and powering on the computer without that chip to see if there was any difference, measuring on the 5V socket directly.

Quote from: Bryce on 15:00, 24 May 22Are you sure you've properly cleaned the power switch and power socket?
Bryce.

Yes, one of the first things just to be sure: The socket has been replaced with a new one and I only measure with the switch overridden (jumper on the pins)

dragon

#38
Quote from: konc on 16:00, 24 May 22
Quote from: dragon on 14:34, 24 May 22
Quote from: konc on 16:10, 14 April 22Behold a fully socketed board that's driving me nuts.
I removed every single chip to power on the computer without it and check the voltage, none made any difference. Still the same 1.1V drop, so no chip is shorted or makes a bad connection.
Unless anyone has a new hunch I don't see what else I can do with it except keeping it for parts (especially now that I can remove any chip easily!) and placing a local ad for a new one.

Have you check the tape relay?. It's connected to the 5v power line when you take out all ics In socket.

That's the Omron black or white box on the top left of the motherboard, right? I removed it completely and measured, no change.
When I say I tried removing every IC I mean one by one, removing the IC, soldering a socket and powering on the computer without that chip to see if there was any difference, measuring on the 5V socket directly.


Mmm. And you have try with all ics unmount at same time and was the same i assume.

Well I don't know if this can be done really. But I'm thinking two tests.

1. Follow the 5v rail path,and divide it in zones. The idea was that in some points of board you solder something that cut the voltage to the rest of the path without cut the track phisically of course. Or maybe there is some jump in the board track  that you can use for that. The idea was find the exact zone that is cause the problem.

2. If you don't use the power socket and try insert 5v in other sites?. As the hole of an ic directly?. this can be mixed with one,for example if you find a jump in 5v track and you can interrupt the power to the rest of the board. You can create a isolated zone and enter the 5v in these zone and view if it drop.

Audronic

I don't Know if the Current has been checked if not Please check how much current is been drawn ?

Keep Safe

Ray
Procrastinators Unite,
If it Ain't Broke PLEASE Don't Fix it.
I keep telling you I am Not Pedantic.
As I Live " Down Under " I Take my Gravity Tablets and Wear my Magnetic Boots to Keep me from Falling off.

konc

Quote from: Audronic on 01:29, 25 May 22I don't Know if the Current has been checked if not Please check how much current is been drawn ?

Keep Safe

Ray
Yes, it's on the previous page, see here: https://www.cpcwiki.eu/forum/hardware-related/cpc-6128-returns-bad-command-on-cat/msg214255/#msg214255

Audronic

#41
Ok I missed it
Ray
Procrastinators Unite,
If it Ain't Broke PLEASE Don't Fix it.
I keep telling you I am Not Pedantic.
As I Live " Down Under " I Take my Gravity Tablets and Wear my Magnetic Boots to Keep me from Falling off.

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