CASIO CZ-101 - Battery mod gone wrong?

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ras_claat
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CASIO CZ-101 - Battery mod gone wrong?

Post by ras_claat » Fri Jun 30, 2017 11:03 am

Hello there.

I've had a CZ-101 for many years, and it's been criminally underused. Lately I've been programming it and loading patches and getting to know it again, and was really enjoying how its sounds contrast with the other gear I have, and what it's possible to do with such a small synth.

The main problem I had with it was keeping it fed with expensive D Cell batteries to maintain patch memory when switched off. I have an RA-3 memory cartridge but found that that was not really reliable, even with a fresh battery. It seemed as though, in certain circumstances, like leaving a power connector attached to the keyboard, the battery of the RA-3 would drain much faster than anticipated (within a week), but I wasn't paying full attention to the situation. It was just a case of powering up the CZ every couple of weeks and thinking 'hang on... sure I had some patches here... I wonder what's happened, damn, I'll use something else today' rather than really thinking about it and troubleshooting.

I read that the CZ 101 has a circuit which stops it powering up if it's getting less than 9(ish)v, but that providing 6V using 4 AA batteries in a holder in place of the D Cells would be enough to keep the memory alive.

I assumed that this was a simple drop-in job, and obtained a 4 AA battery holder with PP3 connector which fitted nicely into the battery compartment. I soldered the leads to the battery terminals - red to + and black to -.

When I plugged in the PSU I had previously been using, the synth didn't power up. I saw that the PSU seemed to have failed, but it was quite old and cheap and I thought that perhaps it had just coincidentally died or that another problem in my electrics had fried it. I plugged in a new PSU and that immediately cut out (red LED on it went off) and I assumed I'd blown it. The PSU was quite hot to touch. A few minutes later I realised that there was protection of some sort on this second PSU which had been tripped, as it started working again.

When I unplugged the synth, the PSU jack was quite hot to touch. On opening the battery compartment, my AA batteries were roasting hot. I immediately removed the wires I'd attached to the battery terminals, but now, with a variety of PSUs, the CZ101 just doesn't want to power up.

Is anyone able to shed light on what I might have done to my CZ and how to remedy it, please? I have had this beauty for many years and am rather ashamed that I might have killed it. :oops:

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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by madtheory » Fri Jun 30, 2017 12:57 pm

Sounds like there is a short in the PSU circuit. That's why the batteries are hot, and the PSU cut out. Might also explain the drain on the RAM cartridge. Could be anything, you'd have to take it to a tech or diagnose the circuit yourself. Can you read a schematic? Do you have the service manual? I would imagine that the transistor circuit responsible for the switching has failed, should be easy to test with a transistor tester.

The RAM cart is very useful on the CZ-101, it expands the memory to 32 patches. On the 3000/5000 you can't do that.

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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by ras_claat » Fri Jun 30, 2017 1:09 pm

Thank you very much, this is interesting.

The synth ran fine from a PSU before I installed this 'mod' - have I pushed a faltering system over the edge by doing so? As in, made the underlying problem more severe?

I can read schematics to a point- slightly concerned that the CZ101 will be beyond my comprehension, though! There's a lot crammed into quite a small space. Also, I have a young child and plenty of other things on my plate, so finding the time to examine it at leisure is quite difficult.

I don't really want to but may have to take it to a tech!

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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by madtheory » Fri Jun 30, 2017 1:45 pm

Well no, it didn't run fine. You had that drain on the RAM cart battery. So it does seem like something has failed. I think it is likely that this will be an easy fix for a competent tech, worth it for a synth of this value.

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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by Rasputin » Fri Jun 30, 2017 1:47 pm

madtheory wrote:The RAM cart is very useful on the CZ-101, it expands the memory to 32 patches. On the 3000/5000 you can't do that.
I believe you mean the CZ-101 has 16 internal patches plus an additional 16 with the RAM cart (which is true), but just to clarify, the RAM cart holds 32 patches but on the CZ-101 only 16 are accessible unless you mod the CZ-101 with a switch to toggle between memory addresses. Pretty easy and useful mod.

I'm not correcting you as you're totally accurate, I just wanted to throw that concept out there.

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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by ras_claat » Fri Jun 30, 2017 2:26 pm

madtheory wrote:Well no, it didn't run fine. You had that drain on the RAM cart battery. So it does seem like something has failed. I think it is likely that this will be an easy fix for a competent tech, worth it for a synth of this value.
You're right... what I mean is that it was broadly operational, with some problems. I think I'll seek out a tech.

The synth cost me £10 to begin with, so don't mind spending a bit on it as long as it doesn't go over the current ebay price of around £150.

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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by madtheory » Fri Jun 30, 2017 5:39 pm

ras_claat wrote:The synth cost me £10 to begin with..
:mrgreen: :mrgreen:
Rasputin wrote: mod the CZ-101 with a switch to toggle between memory addresses. Pretty easy and useful mod.
Oh cool, hadn't heard of that mod :)

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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by ras_claat » Tue Jul 04, 2017 3:18 pm

I've taken the back off to have another look, and it seems as though both DS135 diodes on board MA2M have failed, as they both have slightly blackened legs and are allowing current to flow in both directions.

Please forgive more of my electronic noobery, but - if these failed before my recent 'mod' - are they likely to be the source of the problem I was experiencing with the RA-3 battery draining? And, regardless of when they failed, are there serious implications for components downstream or is it possible that they've just fried without affecting anything else?

Schematic is here(PDF), board in question is on page 4, if anyone has the kindness, time and inclination to take a look.

Thank you!

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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by madtheory » Tue Jul 04, 2017 3:22 pm

It may not be the diodes that have failed, and it would be very unusual for both to fail. Your test simply indicates that there is a short in the system. You could desolder them to make sure. I'll try looking over the schematic later...

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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by ras_claat » Tue Jul 04, 2017 4:27 pm

You are correct.... upon desoldering the diodes, they behave as expected.

I am stumped, and will attempt to find a local tech who isn't already swamped with work.

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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by Mooger5 » Tue Jul 04, 2017 5:08 pm

There´s an EMI filter next to those diodes. I´d remove it, as that component, if shorted, would cause the malfunction you´ve described. It´s my best shot at it, as that section of the service manual is labyrinthic, to say the least.

Good luck!
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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by madtheory » Wed Jul 05, 2017 9:51 am

Mooger5 wrote:...that section of the service manual is labyrinthic, to say the least.
Glad I'm not the only one who thought that! Casio went to a lot of trouble with that auto-sensing lark.

Best of luck getting it fixed.

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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by Mooger5 » Wed Jul 05, 2017 10:25 pm

It´s more the way the circuits were drawn actually. That page is in a different style than the rest of the service manual. It´s just like the Poly 800´s, Lots of closed loops, lines that you start to follow only to discover they lead to nowhere. It turns out those lines are only frames that delimitate the various subsections in the schematic. Drawing those lines with the same width and grey scale as the actual circuit traces was a bad idea IMO.
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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by ras_claat » Fri Jul 07, 2017 2:05 pm

Thank you for the further information... and for picking through the schematic. I will give this a go before sending it away - would it simply be a case of removing this part of the circuit?

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Re: CASIO CZ-101 - Battery mod gone wrong?

Post by madtheory » Fri Jul 07, 2017 2:41 pm

Seems like a good idea but it would not be simple! I wouldn't attempt the experiment on the only CZ I own, especially if one is not well versed in Kirchoff's Laws, transistor theory, linear PSUs, Boolean logic etc.

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