Casio CZ-101 No Power

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Casio CZ-101 No Power

Postby Aquila2 » Thu Jul 19, 2018 2:54 am

I'm new to synths but I am familiar with electronics in general but I cannot figure this out.

I recently acquired a this keyboard at a thrift store for only $10 but it will not power on, adapter or battery. I have fully dismantled it and it looks immaculate. No damaged traces, nothing blown or bloated. All the solder joints are also good. I don't have much info other than that. Any idea on where to start? I appreciate anything.
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Re: Casio CZ-101 No Power

Postby coldwar » Fri Aug 10, 2018 9:45 pm

With Casios, I always start with the 7805 voltage regulator. Will pull my schematics in a bit and take a look for better advice, just seen a lot of them dead for no apparent reason when the rest of the circuit is fine. May want to check any diodes around the input as Casios have outside positive voltage and people notoriously try to plug in their old answering machine adapter which is generally outside negative lol. I have encountered this dozens of times. Will get back to ya with better troubleshooting info later tonight. Good score though. 10 for a CZ101 is a great price for a fun little synth :)
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Re: Casio CZ-101 No Power

Postby Aquila2 » Sat Aug 11, 2018 1:03 am

Thank you for the advice. I await your diagrams.
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Re: Casio CZ-101 No Power

Postby coldwar » Sat Aug 11, 2018 1:34 pm

Aquila2 wrote:Thank you for the advice. I await your diagrams.

http://www.burnkit2600.com/manuals/CASI ... 00_SRV.pdf

Owners Manual
http://manuals.fdiskc.com/tree/Casio/Ca ... Manual.pdf

Check out page 4 of the owners manual where it describes inserting the batteries and the "P button" function and location.
Hopefully it is a matter of pressing that with a toothpick.
Let me know how that goes and we will go from there.
Do you have a Multimeter to test continuity and voltage with?
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Re: Casio CZ-101 No Power

Postby Rasputin » Sat Aug 11, 2018 8:00 pm

Here's a some basic concepts on how to attack this:

Whether or not the batteries or AC adapter are used, there's a common point of the power switch. Since neither batteries nor AC adapter cause the CZ-101 to turn on, we can fairly safely assume (but not certainly) that whatever is wrong is in a part of the circuit which handles both the battery and the AC adapter. In other words, not something simple like crusty battery spring connectors or a cracked solder joint in the DC jack.

While the CZ-101 calls for and appears to be powered by 9V, the circuit really only requires 5V, per se. This means that the CZ-101 takes 9V (from either batteries or the 9V adapter) and drops it down to 5V for all the critical "computing" parts of the circuit (CPU, RAM, etc.)

We should first find out how far the 9V power is getting into the circuit. If we can detect 9V around the battery circuit, 9V around the DC power jack, and 9V at the power button but no further then investigate the power button.

If there's nothing even at the power button, then what @coldwar was saying about the diodes is probably spot on (and I would NOT be surprised if this was exactly what was wrong). Check for two diodes (ds135d) in the power section. If they don't conduct in either direction, they're blown. Again, chances are high here.

If the 9V makes it past the power button circuit, we need to figure out why it's not getting stepped down to 5V. As far as I remember, the CZ-101 does not have a regulator as such (7805) but rather an emitter follower -- in other words, a zener diode that provides a reference voltage to a transistor. We can test this zener diode to see if it's passing the 6V or so that it needs to, and if the transistor that's paired up with it is even seeing the 9V from the battery/AC adapter.

I'm going to assume that 5V is not making it to any of the logic chips, period, because the OP hasn't reported any signs of life.

P.S. As far as the 'P' button goes, it is registered by the CPU the same as any other button, so it requires a working circuit (fully booted CPU and loaded ROM, specifically). It's not the same type of thing as you'd expect from clearing the CMOS battery or reinitializing NVRAM or whatever, unfortunately.
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Re: Casio CZ-101 No Power

Postby Aquila2 » Sun Aug 12, 2018 10:49 pm

Fresh batteries but only reading 5v at the connections, this might be an issue. Also checked the diodes and are functional.
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Re: Casio CZ-101 No Power

Postby Rasputin » Sun Aug 12, 2018 11:53 pm

Aquila2 wrote:Fresh batteries but only reading 5v at the connections, this might be an issue. Also checked the diodes and are functional.


Can you elaborate on that? What do you mean "at the connections"? What about when you use a 9V DC power plug?
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Re: Casio CZ-101 No Power

Postby Aquila2 » Sun Aug 12, 2018 11:56 pm

From end to end of the connected batteries and the leads soldered to the board. Also the center post on the adapter input is broke off so I'll need to put a new one in at a later point.
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Re: Casio CZ-101 No Power

Postby Rasputin » Mon Aug 13, 2018 2:32 am

Aquila2 wrote:From end to end of the connected batteries and the leads soldered to the board. Also the center post on the adapter input is broke off so I'll need to put a new one in at a later point.


When your post said "Casio CZ-101 No Power" I thought that meant the CZ-101 wasn't responding to power, not that it wasn't being given power ;)

I mean... if you're measuring only 5V from six fresh D batteries in series then something is highly wrong with those batteries, and that DC jack is clearly kaput, so that pretty much explains that away.
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Re: Casio CZ-101 No Power

Postby Aquila2 » Mon Aug 13, 2018 2:38 am

They were reading 9v out the box, no idea why it's at 5v now. Will buy more I suppose and update.
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Re: Casio CZ-101 No Power

Postby Janis 1279 » Fri Aug 31, 2018 4:34 pm

hi,
may be i am wrong, but
how good are visually look battery contact places in the battery compartment
how clear are pcb's from residue from old batteries
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