Repair of new CPC464 in my family

[SerErris]

Hi everyone,

I had the joy to grab a Schneider CPC 464 with Vortex F1-X, FD1, DDI-1, X-Module and an SP-512 RAM extension (which is actually filled with 320kb of nice RAM). 

On arrival, the CPC was working, but a little bit unstable, the FD1 and F1-X were both not working. The transformator was makeing a very loud humming noise and other than that it was totally dead (not ready error messages).

So I removed the SP-512 for now and the CPC464 is rocksolid and reads the old Cassettes without a flaw. That is the first tape drive I have seen after so many years, where the belt was not completely wasted. 

So I turned my attention to the F1-X, I do have other working FD1, so I exchanged it and used that for now to test everything.

So first try to gather information, not a lot existing on this particular drive. No Schematics for the power supply or anything.

So I disassembled the drive enclosure and uncabled the drive from the powersupply. Then measureing the 12V and 5V line, and here we have it:

12V was around 7V and 5V was non existent. So powersupply is dead.

Checked the Transformator, which is still good with 2x10,2V output voltage.

Here is the BCB from solder side (mounting is on the other side) with symbols of components in there.

It it is a strange little beast. It should be very simple, but is actually kind of goofy. 

They are using a 2 coil power supply that is connected in the middle (symmetric power supply), but it is not to produce +-10V, but instead they produce 0 V (where - should be) , 18V where + should be, and 9V where GND should be. This is to create the two voltages and GND required for the linear voltage regulators. 

Okay, I just put in my powersupply that I have for my Kryoflux and the drive LED came to live and I could even change the drive and run CAT command.

However the stepper rattled a little bit, but could not move the head. 

So swaped the drive around and unmounted the bottom plate to get access to the head slide and - yes totally frozen. So after carefully moving it with gentle force, It started moving. A good cleanup and regrease would be benefitial, so did it.

Now the drive is fully functional. The great thing about those drives are - they do not have a drive belt. Instead they are direct drive and that works still as day one. 

So now the drive works with a different powersupply.

Ordered parts for the powersupply (bridge rectifier and ELCO caps) and will start to refurbish the Power supply. There should actually not be a lot of things not working on the Power supply. Tested the voltage regulators already and all the fuses, and thats more or less it. 

I will now create a schematics of the powersupply, for anyone to refere to.

[SerErris]

One thing I came accross was unrealiable tape reading at first. But I cleaned it and it is now better.

In between I ran the Input of the PIO to my oscilloscope and found the voltage to be at 3,6 V max. It was looking good and stable, but is 3,6V the expected voltage from the tape drive? Or is there something wrong on the tape circuitry?

[SerErris]

Okay here is the schematics to the above ..

You cannot view this attachment.

What is strange is, that they switched the top primary coil and then the secondary top as well. A more easy to understand setup would have been: connect both primaries in the middle and conecct to mains the top most pin and the bottom most pin, and on the secondary side do the same and you have the same voltages, but just much easier to understand.

Like that:
You cannot view this attachment.

[Audronic]

@SerErris 

Perhaps the the Windings Phase was a problem ?

Keep Safe

Ray 

[SerErris]

I think, we will never find out. But potentially yes, but then I would ask who and why they actually selected this transformer ... But anyhow. Does not make any difference.

Anyone can say something regarding the tape voltage output? 

Is 3.6V normal, or is it low?

Regards
Ser

[Bryce]

How do you know the internal construction of the transformer and the phases?? Did you measure these with a scope? Because they definitely don't make sense and you've mark an AC line with "+9V" ?? How does that work?

I suspect the internal coils of the transformer are very different from what you have in your schematic. My guess is that the coils aren't symetrically connected to the pins as you have assumed.

Bryce.

[SerErris]

Hi, yes I struggeled with this as well.

But it is just a strange way to configure a symmetric power supply.

In normal configurations, this kind of setup is getting used to provide +/-X V and GND. Like here:
https://www.thel-audioworld.de/module/Netzteil/Infos.htm

So the middle PIN of the two transfomer coils is actually providing a stable voltage as both coils are equating the + and - voltage to 0, and that all the time.

That is exactly what is happenning here. So I have 3 Voltage levels - a positive, a negative and a GND level or +/-9V and GND.

And as voltage is really just potentials I can interpret -9V as GND - then the GND will become +9V and the +9V become 18V.

That is all the magic here. The only thing is why they have put this upside down. It is very hard to understand from the schematics, but essentially it is exactly as in the example schematic:

You cannot view this attachment.

My version in different interpretation of voltage levels:
You cannot view this attachment.

BTW: That is very common for any Audio electronic where you need positive and negative voltage levels to do. They just made the trick to change it to two positive voltage levels here.

Hope that explains it.

[SerErris]

Okay, quick update:

After the few parts arrived I exchanged the Bridge rectifier, and the two elkos. On was shorted, the other hat roughly the correct value - but they are all 40 years old - so an exchange would be anyhow good.

All in all, running like new now and drive 100% working.

I love this old tech, the things that can fail, can be easily repaired.