CPC 6128 disk drive error: Disc missing

muchachordo · 19:25, 25 November 24

Hello, good people. I need your help, because I'm about to kill someone. As the title reads, I'm having trouble with the disk drive on my 6128.
To get this error, I do the following:
1. Insert drive
2. Turn on the GT65 monitor
3. Type CAT in BASIC
4. Cry
If I type R for Retry, the same happens. The drive light blinks bright for half a second and nada. No noise from the motor or anything.
Things I've tried:
-Checked for 12V
-Cleaned head and lens
-Ribbon is fully inserted and the right way up
-Good connection between the board and the drive
-Replaced drive belt
-Tried CATing without any disk inserted, same result

Neither motor is getting the required 12V to run. I've got the drive schematics but I'm a little lost as to where to start measuring. The service manual just says "replace drive" and I'd rather use the original disks than a gotek, and "new" drives go for higher than the computer itself. I've searched online and it seems that there are two revisions of the drive, mine is the earliest I think. It has the square PCB, not the one with the long part.

If any of you have any idea as to what could be wrong, please, PLEASE tell me.
Best regards,
Rodrigo

Bryce · 21:20, 25 November 24

Hi, welcome, etc,
Is there 12V getting to the PCB at all? Have you inspected the PCB for dry joints? Especially the header connectors to the motors.

Bryce.

muchachordo · 22:10, 25 November 24

Hi, Bryce. All is good, I'll try to reflow the connectors in the board and in the drive, but visual inspection says that they are ok. Yes, the 12 volts are present and are carried by the connector to the drive. I also had a brainwave. I tried reversing the cable just to try something and the only thing that happens is that the LED stays bright when I give it the CAT order, but I think that tells me that the controller chip in the drive is OK, because if not the drive would be dead right? So maybe the issue is with the part that controls both motors? Maybe? Neither of them are getting the 12 volts, that is, the belt driven one and the one that drives the heads. Would that be possible? Maybe a mosfet of sorts?

Bryce · 22:25, 25 November 24

Yes there is, but it's a cheap discrete NPN Darlington config unfortunately, not a MOSFET. The first thing I'd check is the fuse. There's a PCB mounted fuse on the 12V rail. Check that it's not blown first. It's right behind the power socket.
Also, the 12V only powers the spindle motor, the head motor should move even without 12V.

Bryce.

muchachordo · 22:34, 25 November 24

Fuse seems a-ok. That worries me, as I'm not seeing any movement from the head motor.

muchachordo · 22:44, 25 November 24

Reflowed the connector joints. All connections are good. Nothing. I'm going to try to follow the traces of the computer board itself to see if there are any broken ones.

muchachordo · 22:49, 25 November 24

Just food for thought, would anything bad happen if I jumped the READY(26) or the MOTOR ON (10) with 5V? Just to try things

Rabs · 07:29, 26 November 24

Maybe a silly question but are you sure the fault is with the drive?

McArti0 · 07:48, 26 November 24

Out &FA7E,1 motor on
Out &FA7E,0 motor off

muchachordo · 13:27, 26 November 24

Quote from: Rabs on 07:29, 26 November 24Maybe a silly question but are you sure the fault is with the drive?

Not 100% sure but everything seems to point to that... Rest of the computer works flawlessly and the drive, although VERY briefly, responds to some commands by blinking bright

muchachordo · 13:28, 26 November 24

Quote from: McArti0 on 07:48, 26 November 24Out &FA7E,1 motor on
Out &FA7E,0 motor off

Ok, tried that and measured pin 8 and it's getting a signal, 0V with motor on and 5V with motor off, so I assume the drive is getting the signals but not doing anything with them.

muchachordo · 13:31, 26 November 24

Just checking, the READY pin (26) is at 5V, I don't think that's good right? In the service manual the logic pin is negated, so does that mean that the drive is, in fact, not ready?

muchachordo · 14:08, 26 November 24

Ok, I've investigated a bit more. The model is EME-156, i've found this schematic:

McArti0 · 15:02, 26 November 24

Now find transistor Q1 and see what is happening at the base and emitter.

muchachordo · 15:10, 26 November 24

Quote from: McArti0 on 15:02, 26 November 24Now find transistor Q1 and see what is happening at the base and emitter.

With MOTOR off:
-E:0V
-B:12V
With MOTOR on:
-E:0V
-B:12V
So no change

muchachordo · 15:31, 26 November 24

OK I THINK I'VE FOUND IT
Input of inverter Q2 is changing but not the output, it remains pegged at 12V. Could this be faulty?

McArti0 · 15:33, 26 November 24

Unplug the motor and try again

McArti0 · 15:38, 26 November 24

Q2 you can check by probe+ to +12v and probe- to output Q2.
But if you have always 12v. Q2 is damage and Q1 is damage too.

Ps. Try Q1 cross 12V collector and emiter. Motor should work.

muchachordo · 15:41, 26 November 24

Holy wow, fantastic man! Thanks for the help y'all, I'll keep you updated

muchachordo · 15:44, 26 November 24

ITS ALIVEEEEEE

McArti0 · 16:05, 26 November 24

Easy. Check first if it's not a facehugger.

muchachordo · 16:13, 26 November 24

It CATs now! Accessing the contents of the disk is another story, but the drive looks like frankenstein's monster and an alignment is due. I ordered the parts, when they arrive I'll talk to y'all. Thanks again!

muchachordo · 17:17, 18 December 24

Okay some news:
Q2 was toast and so was Q1. For Q2 I ordered the component and soldered it. For Q2 I couldn't be assed to find the obscure 80s darlington pair and made my own with a couple of BC548 transistors and a 220 ohm resistor in a stripboard and soldered it to the corresponding pins. It works now! At least the motor does.
The drive is capable of reading the contents of the disk but seems to not be able to properly access them. Bear in mind that I think my discs came from a PCW8256, and I think it had a double density drive(?) so I'll try to buy at least a game made for the cpc.
Also I think I saw on a video that you could align the motors, but I've not looked into that for now.
But hey, we're making progress!!!

Bryce · 22:43, 18 December 24

Quote from: muchachordo on 17:17, 18 December 24Okay some news:
Q2 was toast and so was Q1. For Q2 I ordered the component and soldered it. For Q2 I couldn't be assed to find the obscure 80s darlington pair and made my own with a couple of BC548 transistors and a 220 ohm resistor in a stripboard and soldered it to the corresponding pins. It works now! At least the motor does.
The drive is capable of reading the contents of the disk but seems to not be able to properly access them. Bear in mind that I think my discs came from a PCW8256, and I think it had a double density drive(?) so I'll try to buy at least a game made for the cpc.
Also I think I saw on a video that you could align the motors, but I've not looked into that for now.
But hey, we're making progress!!!

There's suitable modern darlingtons with the same footprint. It's only being used as a switch, so they gain isn't all that important. It just needs to be able to handle the required voltages and currents.
Great solution though. I don't think I'd have ever considered replacing a darlington by making my own.

Bryce.

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CPC 6128 disk drive error: Disc missing