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Author Topic: New 6128+ : "disc missing" with new belt + video issue  (Read 434 times)

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Offline reno

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Hello,


So I've just bought a refurbished 6128+ from eBay (a different one from my 1st one with dead RAM, if you followed my other thread  :) )
The seller has done an incredible job with retrobriting / packaging, it really looks like new and I was impatient to test it.


Burnin' Rubber is fine (and I'm going to get a C4CPC from @gerald this week !), but I've tested a dozen floppies and I get "disc missing" for everything  :(
The motor starts and stops fine with "cat", but that's it. There are no other noises from head movement, no read fail, nothing. It's the same with every floppy. When retrying, even on a different disk, it says "disc missing" almost immediately. So it's definitely not the discs.


The seller agreed that I opened the drive to take a look : it's an EME-157, the drive belt was changed obviously. There was just some black residue from the old belt on the capstan, so I cleaned that. And the power connector is a bit more wobbly than on my other CPC, so it could be loose solder points ? I tried pushing the connector down gently but that made no difference.


There is another problem, and I don't know if it's the CPC or my TV :
The TV keeps switching from composite to RGB very quickly (it's mostly composite but it switches to RGB for a fraction of a second, every second or so). I know it switches because the TV says so (it says AV3 / AV3 RGB), also because I can tell the difference (RGB is sharper and has less bleeding to the right of characters).
That's annoying but I don't know if the TV / SCART cable or CPC is to blame here. I can't test this reliably with my other 6128+ because it still has no RAM ;) But I still plugged it in (with no RAM) and got a reddish unstable screen (no vsync it appears). That didn't appear to switch between modes but given how that CPC is broken, I don't know if that tells me much!


Do you have any ideas what might be wrong ?


I would hate to return the CPC given the amazing condition of the case (and accessories) so I'd like to find a solution if possible. On the other hand it is clearly not as a described, as the drive is defective. The video issue worries me quite a bit, as well.

Offline llopis

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #1 on: 22:51, 11 June 19 »
Do a search and look for my thread from a few months back. I had a similar problem with a CPC 6128. I went crazy checking and trying a bunch of things (those things will help you figure out what to look at).
In the end, it was the READY signal that didn't have good connection on the board. It was *that* simple. But it was quite the journey to get there :-) Hopefully that will help you a bit. Good luck!


Here's the start of my thread fixing that disk drive
Here's the start of my thread fixing that disk drive.
« Last Edit: 23:16, 11 June 19 by llopis »

Offline tjohnson

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #2 on: 23:09, 11 June 19 »
Hi Reno, the advice from IIopis re. the ready signal could be good, that is what it does if the ready signal is missing.  Have you any test gear?  You could try pulling the ready signal low by grounding the signal but soldering a jumper between the pin and ground.


Re. quickly switching between composite and RGB my one doesn't do this but I guess it could be your TV, do you have another TV you can try it on?  I assume you bought from RetroByte on ebay?  Where are you based?

Offline reno

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #3 on: 16:46, 12 June 19 »
Hi Reno, the advice from IIopis re. the ready signal could be good, that is what it does if the ready signal is missing.  Have you any test gear?  You could try pulling the ready signal low by grounding the signal but soldering a jumper between the pin and ground.

Thanks for the tip !
So where exactly should I measure / try out a jumper (but no soldering for now I'm afraid, as I could still be returning the Amstrad) ?
I only have a multimeter, but with the time I've been spending on my CPCs and Amigas lately I should get an oscilloscope + desoldering gun, this hobby is a slippery slope :laugh:

But here's some new info :
Today before reading your answers, I've tried the disk drive from my other (never tested, dead RAM) 6128+ in this one, and it worked... mostly.
Getting "read fail" on many many disks, but some do work. Didn't get the "disc missing" issue at all.
So it seems to confirm that something is wrong with the drive in this new CPC !


Except that ... I removed the new drive to return it to the seller, and in the meantime I've left the old drive in the new CPC and closed the case again ... well this time when switching on the CPC, the motor started immediately with the drive LED bright red (not dim red).
I opened the CPC again, fiddled with the connector a little bit and got ... this :o


Okay, suddenly it thinks it's a 464... Fiddled some more... turn it off and on again... and now it works normally again ! (for clarity, this is still the old drive from my other CPC. The new drive always goes "disk missing")


So, this is really strange.
At first it was pretty clear the issue was with the disk drive that came with the new CPC, because it never worked and the old one did straight away.
Then, reading your answers, it seemed the issue could be on the motherboard itself.
And now I've seen the drive from my old CPC also fail at least once with this "LED always on" problem, then come back to normal.


Maybe both drives are faulty in different ways, but the more I think about it, the more I think I should return the entire CPC for a check, not just the disk drive  :'(

Re. quickly switching between composite and RGB my one doesn't do this but I guess it could be your TV, do you have another TV you can try it on?  I assume you bought from RetroByte on ebay?  Where are you based?


I live between London and France. I don't have another TV right now but I could ask a friend. The cable comes from cool-novelties, I wonder if they're fitting resistors in them.
Of course my biggest fear is that the problem isn't the TV or the cable but also the CPC in this case (inconsistent voltage to the SCART pin that selects RGB mode ?). Is that likely / possible ?


Here's a video of what it looks like.
https://www.dropbox.com/s/9jz7thzgvpr35ek/IMG_2328.MOV?dl=0

The thing is, I didn't think there was composite signal on the CPC+ ? It looks very much like it though : the colours are better and there is less bleeding on the characters when TV very briefly switches to RGB.
« Last Edit: 09:19, 13 June 19 by reno »

Offline Bryce

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #4 on: 16:59, 12 June 19 »
Sounds like dry joints somewhere in the system.

Bryce.

Offline reno

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #5 on: 17:20, 12 June 19 »
Sounds like dry joints somewhere in the system.

Bryce.


For the floppy problem you mean, or the video problem ?
So, I guess it's as likely to be on the motherboard as it is to be on the FDD...

Offline tjohnson

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #6 on: 17:49, 12 June 19 »
Sounds like dry joints somewhere in the system.

Bryce.
Hmm strange behaviour, does sound like an issue like that.

Offline Bryce

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #7 on: 09:05, 13 June 19 »

For the floppy problem you mean, or the video problem ?
So, I guess it's as likely to be on the motherboard as it is to be on the FDD...

For the floppy problem at least. Also, what PSU are you using? A weak PSU could cause similar problems.

Bryce.

Offline reno

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #8 on: 09:18, 13 June 19 »
For the floppy problem at least. Also, what PSU are you using? A weak PSU could cause similar problems.

Bryce.


I thought about that too but it’s 2.5A, should be enough I think ?


As for the video problem, could it just be this well known RGB switching signal issue that can be solved with 1.5V power or a capacitor in the SCART cable ? I got my cable premade by coolnovelties, I’ll check if it has any capacitors/resistors.

Offline Bryce

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #9 on: 09:27, 13 June 19 »
2.5A but what quality? Possibly the rail has noise and/or ripple on it that the CPC doesn't like.

As for the video. I've no idea what the wiring is in the cable you bought, but it sounds like it's wrong. They haven't implemented the RGB switching properly.


Bryce.

Offline reno

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #10 on: 10:06, 13 June 19 »
2.5A but what quality? Possibly the rail has noise and/or ripple on it that the CPC doesn't like.

That's the PSU :


It also comes from cool-novelties and sold especially for the 6128+
I can try with another but not sure I've got one that delivers that much power. 2.4A is the minimum, right ?


Quote
As for the video. I've no idea what the wiring is in the cable you bought, but it sounds like it's wrong. They haven't implemented the RGB switching properly.


Maybe the wiring itself is fine except they didn't bother adding a capacitor, which would make it work with some TVs but not others, right ?
They're a quite high profile seller of retro cables and I doubt they would have got the wiring completely wrong or they would get loads of complaints ! But I'll open it and check. BTW I didn't think the 6128+ had composite at all ? How could the TV possibly switch from that to RGB ?

Anyway, I wanted to make sure that this problem is very unlikely to come from the CPC itself. Can you confirm ?
« Last Edit: 10:17, 13 June 19 by reno »

Offline tjohnson

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #11 on: 10:27, 13 June 19 »
Looks like the psu is this one


https://cpc.farnell.com/stontronics/t6349st/ac-dc-power-supply-5v-2-5a-2-5mm/dp/PW04065?st=2.5a%20psue%205v


My cable comes from cool novelties too but doesn't exhibit these issues.  As I understand it the scart will default to composite unless there is a certain voltage on the switching pin in which case it switches to rgb mode so something could be happening with the voltage on that pin to cause the TV to switch between composite and rgb.

Offline reno

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #12 on: 10:51, 13 June 19 »
Looks like the psu is this one


https://cpc.farnell.com/stontronics/t6349st/ac-dc-power-supply-5v-2-5a-2-5mm/dp/PW04065?st=2.5a%20psue%205v


My cable comes from cool novelties too but doesn't exhibit these issues.  As I understand it the scart will default to composite unless there is a certain voltage on the switching pin in which case it switches to rgb mode so something could be happening with the voltage on that pin to cause the TV to switch between composite and rgb.


It could be that my TV has a different voltage threshold for switching to RGB than yours.
I've just measured 0.63V between pins 16 & 18 of the SCART cable (according to this schematic this is where 1.5V should be applied : http://www.cpcwiki.eu/imgs/5/50/Plus2SCART_-_RGB.jpg)

Could it also be an issue with the signal coming from the CPC, or just a lack of capacitor there ? :/ That's my biggest worry.


Offline Bryce

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #13 on: 11:03, 13 June 19 »

It could be that my TV has a different voltage threshold for switching to RGB than yours.
I've just measured 0.63V between pins 16 & 18 of the SCART cable (according to this schematic this is where 1.5V should be applied : http://www.cpcwiki.eu/imgs/5/50/Plus2SCART_-_RGB.jpg)

Could it also be an issue with the signal coming from the CPC, or just a lack of capacitor there ? :/ That's my biggest worry.

The minimum current to run a Plus is about 1.6A not 2.5.

TV's don't have different switching voltages for the SCART inputs they are a standard: 0V to 0.4V = Composite, 1V to 3V = RGB.

0.63V sounds like enough, but you probably measured it without a load, so it may actually be lower.

Bryce.

Offline reno

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #14 on: 11:09, 13 June 19 »
The minimum current to run a Plus is about 1.6A not 2.5.

Ok, I got that 2.4A info from the wiki actually. 1.6A even with the FDD ?
TV's don't have different switching voltages for the SCART inputs they are a standard: 0V to 0.4V = Composite, 1V to 3V = RGB.
0.63V sounds like enough, but you probably measured it without a load, so it may actually be lower.




Thank you again.
Yeah, I'll need to look at the schematics to find where to measure this under load on the CPC side.
Could this low voltage be an issue with the CPC then ?

Offline Bryce

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #15 on: 11:17, 13 June 19 »
The CM14 could supply 2.4A, but this was dimensioned to allow for additional expansions etc. The computer itself (including FDD access) only pulls about 1.4A as far as I can remember.

You'll have to measure the voltage between pins 16 and 17 on the SCART plug while it's plugged into the TV to find out what the real voltage is. And no, it's not an issue with the CPC, rather how the cable was made.

Bryce.

Offline reno

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #16 on: 18:32, 17 June 19 »
The CM14 could supply 2.4A, but this was dimensioned to allow for additional expansions etc. The computer itself (including FDD access) only pulls about 1.4A as far as I can remember.

You'll have to measure the voltage between pins 16 and 17 on the SCART plug while it's plugged into the TV to find out what the real voltage is. And no, it's not an issue with the CPC, rather how the cable was made.

Bryce.


Thanks, are you sure it's pins 16-17 ? Does that mean the diagram on the wiki is wrong ?

Offline Bryce

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Re: New 6128+ : "disc missing" with new belt + video issue
« Reply #17 on: 09:21, 18 June 19 »

Thanks, are you sure it's pins 16-17 ? Does that mean the diagram on the wiki is wrong ?

Sorry, I meant 16 and 18.

Bryce.