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General Category => Technical Support => Topic started by: vasilisk on 13:25, 16 February 21

Title: Sudden problem with 3" drive
Post by: vasilisk on 13:25, 16 February 21
This morning, and without any warning signs, the drive is not reading the discs.
At "cat", is trying to load for a few seconds and then pops "bad command". I tried a spare 3" drive, and is doing the same.
Both drives have therir belt changed (last year) and parts greased. The first drive, was working without problems all week. The spare hasnt been used since the service.
If I eject the disc while is trying to load, and before the "bad command" it pops drive A is missing. Which I think is normal.
I opened the cpc, and while "cat" I noticed that the center is spining, but the shaft is not moving up and down. In both drives.
Any suggestion?
Title: Re: Sudden problem with 3" drive
Post by: Bryce on 13:52, 16 February 21
Either a problem with the flat cable or the driver IC (74LS38) has failed.

Bryce.
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 13:54, 16 February 21
Either a problem with the flat cable or the driver IC (74LS38) has failed.

Bryce.


Any way to test each of them?
Title: Re: Sudden problem with 3" drive
Post by: Bryce on 14:27, 16 February 21
You can check whether the STEP signal is being sent from the chip and if it is, trace the signal to find out where it's not getting any further.

Bryce.
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 14:32, 16 February 21
You can check whether the STEP signal is being sent from the chip and if it is, trace the signal to find out where it's not getting any further.

Bryce.


Sounds complicated. Do I need any special equpiment for this?
Title: Re: Sudden problem with 3" drive
Post by: Bryce on 16:00, 16 February 21
A scope would be best, but it's slow enough to check with a multimeter.

Bryce.
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 16:03, 16 February 21
A scope would be best, but it's slow enough to check with a multimeter.

Bryce.


Is it too much to ask for some guidelines, concerning the approach with the multimeter?
Title: Re: Sudden problem with 3" drive
Post by: Bryce on 16:13, 16 February 21
Measure the voltage between GND and pin 8 of IC208. It should be at 5V. If you do a CAT it should jump between 5V and 0V, so will show up as around 2.5V on the multimeter.

Bryce.
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 16:28, 16 February 21
Ok. Red arrow is pin 8. If I am not mistaken. GND ?

edit
If by GND you mean the calbe that connects the motherboard at the right with the metal sassi of the drive, then it is 4.77







Title: Re: Sudden problem with 3" drive
Post by: Bryce on 17:46, 16 February 21
Ok, it should go low (0V) each time it needs to step (move) the head.

Bryce.
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 17:53, 16 February 21
Ok, it should go low (0V) each time it needs to step (move) the head.

Bryce.


Voltage stays as it is and head is not moving
Title: Re: Sudden problem with 3" drive
Post by: Bryce on 18:01, 16 February 21
Then that chip needs to be swapped.

Bryce.
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 18:03, 16 February 21
Then that chip needs to be swapped.

Bryce.


So this chip is responisble for the drive?
I see that IC206 uses the same chip. Is this identical to IC208?


I checked this thread also and the IC206 shows the same misreadings


https://www.cpcwiki.eu/forum/hardware-related/fixing-floppy-drives/125/
Title: Re: Sudden problem with 3" drive
Post by: Bryce on 19:18, 16 February 21
IC206 is the same chip and also responsible for signals to the FDD, but it performs different tasks, so you can't compare pin results.

Bryce.
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 19:21, 16 February 21
IC206 is the same chip and also responsible for signals to the FDD, but it performs different tasks, so you can't compare pin results.

Bryce.


In the thread I mentioned, @Audronic (https://www.cpcwiki.eu/forum/index.php?action=profile;u=1169) posted some voltage changes during CAT, for the IC206. These also dont happen Maybe they need both replacement.


Can you point me where I can buy these? I see many different versions. Do they need programming?
Title: Re: Sudden problem with 3" drive
Post by: Bryce on 19:32, 16 February 21
No programming required. What different versions are available? Post a link to the ones you want to order. Have you experience in chip swapping? If not get someone with experience to do it.

Bryce.
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 23:16, 16 February 21
https://www.ebay.co.uk/sch/i.html?_from=R40&_nkw=74ls38&_sacat=0&_sop=15 (https://www.ebay.co.uk/sch/i.html?_from=R40&_nkw=74ls38&_sacat=0&_sop=15)


Are any of these compatible?
Other site maybe?


I have someone experienced to do it. I wasn't going to  8)
Title: Re: Sudden problem with 3" drive
Post by: Bryce on 23:41, 16 February 21
All of the through-pin ones in that list are fine. Buy two. If you're going to take out 208, you might as well swap 206 while you're there.

Bryce.
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 23:55, 16 February 21
All of the through-pin ones in that list are fine. Buy two. If you're going to take out 208, you might as well swap 206 while you're there.

Bryce.


Thank you. In an another thread, there was a discussion for fake/original chips. For this case do I have to worry about finding specific ones?
The fact that the head is not moving up/down, is responsible this chip? Could it be something else? Not enough voltage maybe? Although I tested with both the ctm644 and external psu.


Is this chip ok?

Title: Re: Sudden problem with 3" drive
Post by: Bryce on 00:04, 17 February 21
No, it's unlikely to be a voltage issue. If the 5V rail couldn't turn the motor, the voltage would drop and the CPC would crash.
As for fakes, you've no worries with this part. They are still produced in masses and are low cost. There would be no profit in cloning them.

Bryce.

Edit: I'd pay more for local parts. Shipping from China is extremely slow at the moment. You could be waiting months for them to arrive.
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 00:07, 17 February 21
No, it's unlikely to be a voltage issue. If the 5V rail couldn't turn the motor, the voltage would drop and the CPC would crash.
As for fakes, you've no worries with this part. They are still produced in masses and are low cost. There would be no profit in cloning them.

Bryce.

Edit: I'd pay more for local parts. Shipping from China is extremely slow at the moment. You could be waiting months for them to arrive.


Ok. But is the above code ok? In case I ask the local electronic shops
5v? Isnt the drive powered by 12v?
Title: Re: Sudden problem with 3" drive
Post by: Bryce on 00:16, 17 February 21
The only bit that matters is the base code and the case type. This is what the rest means:

SN - Manufacturer code (SN = Texas Instruments) - Base code 74 tells you it's a commercial TTL chip. The LS tells the types of gates inside (LS = Lowpower Schottky) and the 38 tells the function (38 = 4x NAND gate). The N ist the package type (N = Through pin). The other row of numbers/letters tells you where (production plant) and when (usually week and year) it was produced.

Bryce.

Edit: The motor that spins the disk is 12V, but the head motor is powered from the 5V rail.
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 20:20, 18 February 21
These 74ls38 chips, can they be converted to socketed ones?

Title: Re: Sudden problem with 3" drive
Post by: tjohnson on 00:45, 19 February 21
Yes, although they rarely fail so probably not worth it.
Title: Re: Sudden problem with 3" drive
Post by: Audronic on 07:27, 19 February 21
@tjohnson (https://www.cpcwiki.eu/forum/index.php?action=profile;u=2129)


Any Chip that talks to the outside world is always suspect
For about 3-5 Dollars its worth it for piece of mind


Keep Safe


Ray
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 09:31, 19 February 21
Yes, although they rarely fail so probably not worth it.


it seems that we are in the "rarely" case  8)
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 16:30, 20 February 21
When the cpc is on (standby), what voltage these cables must have?
Title: Re: Sudden problem with 3" drive
Post by: tjohnson on 16:50, 20 February 21
One provides 5v and one 12v.  The 12v is the motor and the 5v is the logic, they are reversed from a normal PC floppy drive connector, I believe the red is 12v and orange is 5v.
Title: Re: Sudden problem with 3" drive
Post by: vasilisk on 18:47, 20 February 21
Unless I'm doing something wrong, I am not getting 12 volts on the red cable. Orange cable is at 5 volt.
Title: Re: Sudden problem with 3" drive
Post by: tjohnson on 23:18, 20 February 21
Does the motor spin up?


I assume this is a 6128 and is connected to an original Monitor that is providing 12v and 5v, these are separate, the 12v is via a cable from the computer plugged until the monitor  and the 5v is via a cable from the monitor plugged into the computer.


Check your Monitor is providing 12v, it's centre negative from what I recall.
Title: Re: Sudden problem with 3" drive
Post by: tjohnson on 01:06, 26 February 21
@vasilisk (https://www.cpcwiki.eu/forum/index.php?action=profile;u=2004) did you fix it?