CZ-1000 lights and display will not turn off until power is disconnected.

[IanB]

45 minutes ago, HELVETIA said:

That is why I think he just  pull the power plug as i think it's not worth the troubles lol  

 

Well maybe, but one fault can lead to another so it's better to fix them if you can

[lulu_joe]

All, thanks again for the input. I will look at the schematic a little tonight. Too late and too tired to test. I will report back ASAP, though. JoeF.

[lulu_joe]

Hello. So I probed the additional points that folks suggested.

A works as expected.

B did not pass. Plug in and turn on it is Low. Press off and it goes High. Turn on again goes Low.

F Goes High when switched on and stays high until unit is unplugged.

G Plug unit in and turn it on, this goes High and stays high until unplugged.

 

Thanks for looking. Any clues? JoeF.

 

[Jokeyman123]

Sorry I did not study the schematic until now. T1, T8, T9 -transistors blow like fuses-very easily. There is also a zener diode in that part of the circuit that is labeled, rather conspicuously "power down detector". I am assuming this is where you are looking? I see T7. You might research which parts commonly fail in the Czs-there may be some online info-I suspect now that I have studied this, transistors-in older circuits, these were always pretty frail. i seem to recall others who did troubleshooting on the CZs-replacement parts seem to fall in the transistor category if you can find the right ones.  You seem to be getting close to-all you need is one open or shorted component-try to trace voltages with power on-be careful! You might discover a path with no or unusually high voltage where it should have voltage-or voltage where it shouldn't which looks like you are doing-which can lead you to the defective component. And of course the old trick-temperatures-if one temperature of a transistor is colder or hotter than others (not the power regulator) this could indicate a shorted or open transistor. Feel the resistors too-if any are hot to the touch-these are defective. Easy to check resistors in circuit with power off for approximate resistance.  

[IanB]

Okay, I think we're narrowing it down now. Check for the 0.6millisecond "low" pulse at point M at power off. This is the CPU board signalling back that it's okay to shut down. If that is okay, now check if point E swaps from Low to High and point D swaps from High to Low as a result of that power down pulse.

If you haven't got the pulse at M, check the two resistors connected to it are okay.

My current guess is you will find the pulse at point M and the problem is in the logic between there and point F. And if D and E are swapping correctly, the fault will be between D and F.

[lulu_joe]

9 hours ago, Jokeyman123 said:

conspicuously "power down detector"

Where do you see this? Quadrant F,4 on card MA2M. I can’t find it or the zener diode? JoeF.

[HELVETIA]

lulu_jou        do you know if this function works ?   

[lulu_joe]

I did try the APO switched on and the CZ stays on. I will try those other tests once ASAP. To. JoeF.

[Jokeyman123]

lulu--it is on page 2 of the schematic-towards the bottom of that page marked M4152-MA1M, CN3M. The schematic in that section shows a zener diode-small z shaped line above the triangle-standard zener schematic diagram. I also can only guess what the IC is in that section. and if there is any kind of timer IC anywhere in that small section of the circuit-old circuits used simple 8-pin 555 chips to create a timer in a circuit.  If that IC is a timer chip-that could be the source of this problem, or adjacent components causing the timer chip to not function correctly, if it is a timer chip. it isn't labeled in the schematic-but it looks like it might be a simple 8-pin DIP IC. The triangle shape in the schematic in that section is a standard representation of  a simple logic chip, usually an 8-pin. without a number designation-I couldn't be sure. too bad there is no parts list around somewhere.

[IanB]

The power down detector isn't the problem I think. It just detects an unexpected drop on Vdd and initiates a shutdown if that occurs. The chip is a comparator. Big triangles are op amps and comparators. If it was malfunctioning it would cause a shutdown not prevent one. So I think the fault is in the logic on the power board that responds to a shutdown request from the CPU.

[Jokeyman123]

You are eliminating everything it cannot be. Keep pecking away....! Could a simple bad solder in one of the cables-you said these are hard-wired, not socketed, right? Unfortunately with a repair like this-unless you can narrow it down, like looking for a needle in a haystack. There could even be a shorted diode or transistor in one of the ICs causing one lousy data line to stay open or closed. 

[lulu_joe]

OK. More probing.

M went high when powered on but never came down or produced the downward pulse.

D never comes down after unit is turned on

E goes down but never back up

 

Again, thanks for looking. Any suggestions? JoeF.

[IanB]

I have a red handprint on my forehead. I went back through the thread. Previously you said K goes high at power off, but L doesn't go low. L is the Interrupt pulse to the CPU to tell it to shut down, and is a negative edge, so if L doesn't go low the CPU never knows to respond with a shutdown. There isn't much between K and L, just a resistor and 1/4 of a 4011 NAND gate chip, so if the 4.7K resistor is okay (check with multimeter) and there are no damaged PCB traces, then it has to be that NAND chip that has malfunctioned; it's quite possible for just one of the four gates it contains to fail. It's one of these-

 

http://www.ti.com/product/CD4011B

 

and they cost peanuts. Mind you, peanuts are in short supply at the moment due to the panic buying, but I don't think there's yet a mad rush to get CMOS logic chips so we should be okay.

So if you locate that chip, check the voltages at pins 11, 12 and 13. 12 and 13 are connected together and it's basically just an inverter, so when 12 & 13 are high, 11 should be low and vice versa. If they aren't, that's our baby! You should be able to test it by just "piggybacking" a new 4011 onto the old one with all the pins touching their counterparts. Be careful as CMOS is very static sensitive, and it's probably static that has killed the current one. If you don't have a grounding wrist strap, make sure the hand you're handling them with has been touched to grounded metalwork before you touch them.

Also, if you need to desolder the 4011, the easiest way will be to snip all the pins and desolder them one at a time.

 

Let me know. It would nice to get a result with this before civilisation collapses.

[lulu_joe]

Hey there,  I am reprobed some things because as I said originally I had never used an oscilloscope as a test instrument before, merely entertainment when looking at audio signals.

But, I think I have made a breakthrough for this problem thanks to all your help but particularly you IanB.

If I short 4011 pin 11 with 10 the unit shuts OFF! Pin 10 is low.

But, as you said the 4011 is suspect. Pin 11 and 12 both go high and low as the on off button is pressed. High when off, low when on. Pin 11 never changes.

K goes low when plugged in. High when the unit is turned on and low when turned off.

L is low when plugged in. Goes high when turned on and stays high when turned off.

 I know I shouldn't be complaining when I still have a job to go to, since most of my friends got shutout Mon., but I just want to stay home and solve this puzzle and make killer bass sounds with this synth again!

Thanks again. JoeF

Edited March 20, 2020 by lulu_joe
Wrong info.

[IanB]

Yes, I'm now pretty much certain that the 4011 chip needs replacing (just for completeness check it has power but I doubt that is the problem, power is on Pin 14 (top right from top view of chip) and ground (0V) is on pin 7 (bottom left).

If you look on the main CPU board MA1M you'll see the CPU which is labelled upD 7811G-120. The CPU's NMI (non maskable interrupt) on pin 25 is pulled high by a 2.2k resistor (which for shorthand they've drawn a little circle with a vertical line down- see the "key" bottom left of the schematic) connected to Vdd. So when Vdd goes high, that line is pulled up. It's the job of that gate we're looking at in the 4011 to pull it down when K goes high. That signals the CPU to run its NMI routine which sends a response (the pulse at M) when it's ready to shut down. Since L never goes low, the CPU never knows and never replies.

 

So as I said, check the 4011 has power and if so, it must be that chip which has failed, so that needs replacing.

 

*EDIT* Having just posted that, can you recheck K? On your earlier post you said it's LOW when the unit is on, that is it should stay low until you switch off. Now you said it's high when the unit is on. Which is it?

 

*EDIT AGAIN* Just to clarify, pins 12 and 13 should be at the same level as point K as they are connected via a 4.7k resistor. So when you switch off, K should go from low to high, and so should 12 and 13. If K is different to 12/13 it must be the 4011 or the 4.7k resistor. With the unit unplugged, test continuity with a multimeter between K, the resistor and the 4011 pins.

[lulu_joe]

I will recheck K and all I reported today though I am confident of today’s readings. But, if I probe the pins of the 4011, pin 11 is not always the opposite of 12 and 13. And it should be if it is a NAND. Correct?

 Also, not to be too big a nudge. But, if I need to find replacement transistors where can I find a cross reference. And, is 2sc17400 the same as 2sc1740?

 Tx. JoeF.

[IanB]

Yes, 11 should be the opposite of 12 and 13, but also crucially 12 and 13 should be the same as K. So please check that, and that the 4011 has power, and all the continuity I suggested.
 

I would think they are the same transistors, but they're pretty general purpose anyway. Most of them are just acting as switches.

[lulu_joe]

Hello all.

 I rechecked K and it is low when the power supply is plugged in and low when the unit is switched on, then high when switched off. It does not fall. It just stays high until the unit is switched on again.

K and pin 13 and 12 are in the same state always. And pin 14 is sitting at right around 5V. Pin 7 is 0V.

I am ordering a couple 4011s. JoeF.

[IanB]

@JoeF Yes, I think we have a winner with that 4011  

 

Do let us know how it goes. Also once you're up and running feel free to try my free CZ Patch Editor for Windows 10. It's called "VZV CZ" and you can find it on the Windows 10 Store. If you're using Win 10, otherwise don't worry heh.

[lulu_joe]

Hello and thanks to all. IanB you got it! Put in a new 4011 and we are playing again. Cool sounds already. I love this synth. JoeF.

[lulu_joe]

 Doh! Solved one and another problem just showed. Oh well, going to catch my breath before I attack this again.

 Turned off and on a bunch then sealed it up, programmed a patch and when I came back and turned it on it powers up and all the lights come on, the display remains blank and no sound or controls work. I tried repowering with P button pressed but nothing changes. JoeF.

[IanB]

Oh no, that is so frustrating!

It's possible something got hurt when you were sealing it up. Well, at least some of it's still working. 😖

[IanB]

My first guess is there's no power on the main board, which is Vdd. We know (I think) Vdd itself is fine on the power board, so I think the place to start is the power and ground connections on MA1M the main board. Part of the reason for thinking this is that the display gets its power from that board and as it's an old LCD you ought to see some change of contrast at power on if that has power.

[Jokeyman123]

Reason for my earlier posts. Often if one component is damaged, you might want to consider what damaged it in the first place-transistors are frail and can blow easily by themselves (my old TEAC 3340 built with discrete components including many transistors) has needed several transistors replaced. Ian correct me if I'm off-base-I would look at whatever circuits the bad transistor is sourcing in and out. and if something regulating power to that is also bad-or often if one transistor went, might be 1-2 more that were marginal, and when you replaced the one, it blew another.  Like Ian said, most transistors are either bias switches, or voltage controls. Glad this isn't on my bench! 

[IanB]

@Jokeyman123 It may well be that but I'm a bit more optimistic for a couple of reasons. This is all logic level stuff so there's less chance of a cascade failure of that type; plus it worked fine on the bench but then immediately after reassembly did not work, which suggests to me that something was disturbed during reassembly. These are old boards after all, with joints that were all soldered over 30 years ago! So my guess is one of the solder joints on an interconnecting cable has failed.

This kind of "fail after fix" is particularly demoralising, but hopefully we're on the last lap now!