JX3P just plays single repeating tone and some of the buttons change it?

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nightcheese
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JX3P just plays single repeating tone and some of the buttons change it?

Post by nightcheese » Sat Aug 10, 2019 6:25 am

So I've literally been trying to fix this issue for years with no luck and figured as a last ditch effort I'd ask the experts...

My JX3P was working just fine until one day when I accidentally left it on for a few hours and when I came back it was just doing this. Now this is all it ever does: https://soundcloud.com/inceptioj/my-jx3 ... -does-this

All the patch selector lights flash in time with the tone, the "tape memory" and "D bank" lights stay solid. None of the keyboard keys do anything.

Holding 4, 5, or 6 turns it into a harsher wave (saw?) and puts it up an octave.

Holding 9 makes it softer and puts it up an octave.

Holding 4, 5, or 6 and 9 makes it into kind of a combination of both.

A couple of times I've managed to get it into a mode where it goes quiet and the patch select buttons light up individually one by one but with some of then constant, and then it goes back to doing what it always does.

As far as I can tell none of the components look broken, no leaking caps or anything. I've reseated all the little connectors, I've cleaned the PCB, and the voltages seem fine too. I've cleaned the switches, tested continuity on them and they all seem okay (although I might have done it wrong).

It almost seems like it's going into some sort of test mode but I can't figure out why or how to get it out... Has anyone experienced something like this before or could suggest a diagnosis method?

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Re: JX3P just plays single repeating tone and some of the buttons change it?

Post by Rasputin » Sun Aug 11, 2019 1:10 am

Spitballin' here, so this could be wildly inaccurate, but it's something to think about at least.

One of the seven JX3P tone select buttons is stuck on, either physically/mechanically or electrically. This would force the JX3P into test mode at every power on event.

It may be possible to disengage test mode by unplugging the panel board connection from the mainboard. I think the music keybed would still respond although obviously patch selection would be impossible. Still, it would narrow down the source of the issue to the panel board if you could play one patch normally by doing this.

Disconnect CN10 from the mainboard. If that doesn't help, try disconnect CN6 either with CN10 or just by itself.

You mentioned TAPE MEMORY which is the way test mode can be entered ordinarily. If you left the JX3P and came back with it behaving like this then it would seem to indicate TAPE MEMORY had to have automatically engaged, but my understanding is that TAPE MEMORY and at least one tone select button would have to be "on the blink" for this to happen.

In my mind, it points to either a panel scanning issue or a power supply issue. PSU problems can make the oddest things happen which would otherwise be inexplicable.

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Re: JX3P just plays single repeating tone and some of the buttons change it?

Post by nightcheese » Sun Aug 11, 2019 6:34 am

Hmm okay, disconnecting any combination of CN10 and CN6 doesn't change anything. With just CN6 and no CN10 the same lights are lit but the buttons don't do anything, and it makes the same sound...

I guess that eliminates the front panel from causing the issue? Unless it requires a certain signal from the front panel board to disengage the test mode?

I've checked the reference voltage as per the service manual and it was correct, apart from that I'm not sure how to check for PSU issues.

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Re: JX3P just plays single repeating tone and some of the buttons change it?

Post by Rasputin » Sun Aug 11, 2019 4:13 pm

nightcheese wrote:
Sun Aug 11, 2019 6:34 am
I guess that eliminates the front panel from causing the issue? Unless it requires a certain signal from the front panel board to disengage the test mode?
Not so much a signal from the panel board to disengage test mode, but more that the mainboard sees buttons 1-6 and 9 (either individually or any combination) as being permanently on, regardless of the functionality or state of the panel button board.

That leads us to a problem with one of the ICs on the mainboard. Unfortunately, I don't have a particular interest in the JX3P so I don't know exactly how everything (mostly test mode) is supposed to behave under normal circumstances.

One of the curious things is that the tone selector buttons do work to some degree, but I don't believe they should normally need to be held to function.

The way you've described it as operating makes me think the JX3P immediately sees another button press any time it receives a key-up event from any button you're holding down. That is to say, '9' will work properly upon key-down, but as soon as you release the button (key-up), it allows the key scan to detect a permanently depressed button again which puts you back into another test mode.

Points of interest are:

- IC34 (LS138), panel button scanner
- IC46 (40H245) - music keyboard and panel button read buffer
- and maybe IC53

IC34 is tied into CN6. If you unplug CN6 then that should disconnect/kill the buttons in the panel board, so none of the buttons should show as up/down regardless of the state of IC34 or whether or not any buttons are pressed. This is because IC34 drives the panel button matrix by sequentially selecting which set of buttons to check (arranged in a column).

Likewise, CN10 unplugged kills the buttons because that determines which specific buttons (arranged in a row) are on/off within the currently checked set of buttons (as determined by IC34/CN6).

In other words, CN10 reports which rows have buttons pressed, and CN6 determines which column is being checked. The intersection of rows and currently checked column determines which button is up or down.

The state of the buttons/key rows are held in IC46 so the CPU can read them. If there is a problem with IC46 then it could be reported that buttons are permanently on/off even though no buttons are pressed (or even connected).

Some buttons work which means that IC34 and IC46 must at least semi-functional. Since at least some buttons respond by a press/release then that means the corresponding rows for those buttons on IC46 cannot be stuck, or else they could not be toggled.

Row SW0 (IC46 pin 2) = 1 and 9
Row SW1 (IC46 pin 3) = 2 and 10
Row SW2 (IC46 pin 4) = 3 and 11
Row SW3 (IC46 pin 5) = 4 and 12
Row SW4 (IC46 pin 6) = 5 and 13
Row SW5 (IC46 pin 7) = 6 and 14
Row SW6 (IC46 pin 8) = 7 and 15
Row SW7 (IC46 pin 9) = 8 and 16

Tone buttons 4, 5, 6 and 9 respond so that means that IC46 pin 2, 5, 6 and 7 cannot be stuck. If only tone 1-6 and 9 can force test mode at boot--and we've also determined that the pins corresponding to tone buttons 4, 5, 6, and 9 cannot be stuck--then that leaves the pins corresponding to tone select buttons 1, 2, or 3.

Tone button 1 and 9 share IC46 pin 2, so since tone 9 works then we can eliminate pin 2 (and therefore tone button 1), leaving tone 2 or 3 as suspect. Tone 2 and 3 use IC46 pins 3 and 4, respectively.

If pin 3 or pin 4 of IC46 is stuck then either tone 2 or 3 will register as being pressed each time the CPU goes to check them. However, if IC46 pin 3 or pin 4 is stuck then many other buttons would also show as being pressed permanently, as multiple columns share the same row which corresponds to the stuck pin.

Pin 3 stuck? Then 2, 10, MUTE, and GB would all automatically trigger!
Pin 4 stuck? Then 3, 11, HOLD, and ED WRITE would all automatically trigger!

This would result in the JX3P going haywire, so I'd start with a logic probe or 'scope on IC46 pin 3 or 4. Maybe you'll find one of them never toggles between 0V and 5V.

Rhino would probably be much better help here, but I'm not sure if he's available.

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Re: JX3P just plays single repeating tone and some of the buttons change it?

Post by dorrismillerrr123 » Mon Aug 12, 2019 9:39 am

Maybe this is a kind of CPU issue?
In general, this is a good opportunity to learn how to repair a synthesizer. If he was mine, I would have stolen and looked for any damage there?
Here is a link to the service manual - http://www.synfo.nl/servicemanuals/Rola ... _NOTES.pdf

Image

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Re: JX3P just plays single repeating tone and some of the buttons change it?

Post by nightcheese » Sat Aug 17, 2019 1:15 am

Thanks for your help, that sounds like a really good avenue for investigation.

Just to verify it's not a power thing I measured the voltages across the PSU rails by sticking a multimeter over D1 and D2 and D3 (I'd only measured the 5v on the mainboard) and both the 15v and 5v rails were right +- like 0.2v. I think this is the correct way to do this (I'm very new to this).

I also touched up some solder joints on the mainboard which looked like they could be dry.

Looks like I might need to go buy a logic probe to test those ICs...

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Re: JX3P just plays single repeating tone and some of the buttons change it?

Post by nightcheese » Sun Sep 08, 2019 1:06 am

I've finally gotten a logic probe! Had to order one from China since they were discontinued at the local electronic store...
Rasputin wrote:
Sun Aug 11, 2019 4:13 pm
Row SW0 (IC46 pin 2) = 1 and 9
Row SW1 (IC46 pin 3) = 2 and 10
Row SW2 (IC46 pin 4) = 3 and 11
Row SW3 (IC46 pin 5) = 4 and 12
Row SW4 (IC46 pin 6) = 5 and 13
Row SW5 (IC46 pin 7) = 6 and 14
Row SW6 (IC46 pin 8) = 7 and 15
Row SW7 (IC46 pin 9) = 8 and 16
After disconnecting CN10 and CN6 all of the pins along the right hand side of IC46 (so pins 2, 3, 4, 5, 6, 7, 8 I think?) were 1 except pin 9 was 0. Without CN10 and CN6 plugged in they should all be 0 right since no key presses should be being read from the panel?

Also, plugging in CN10 and CN6 and probing IC46 seemed to indicate that IC46 wasn't seeing any keypresses. None of the pins changed state no matter what buttons I pressed. And also IC34 didn't seem to change state no matter what buttons were pressed.

I'm not sure if it matters (or if it just indicates CPU ticks or something) but the "pulse" light on my logic probe flashed in time with the repeating sound on many pins, and some of the pins on the other side of IC46 stay on 1 but go to 0 for a fraction of a second before each iteration of the repeating sound (if that makes sense).

Does this indicate that IC46 is broken, or IC34, or both? Or could it be something else further up the chain?

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Re: JX3P just plays single repeating tone and some of the buttons change it?

Post by Rasputin » Mon Sep 09, 2019 2:32 pm

nightcheese wrote:
Sun Sep 08, 2019 1:06 am
Some of the pins on the other side of IC46 stay on 1 but go to 0 for a fraction of a second before each iteration of the repeating sound (if that makes sense).
To begin to answer that, it might be helpful to look at some theory of operation. Snooze... :D

THEORY OF OPERATION

What is IC46 and why should we care what it's doing?

It doesn't do a whole lot, actually. It's only role is to take in 8-bits of data and present it to the data bus whenever the CPU needs to read the key/panel data. In this case, the data is the state of either the panel or music keyboard switches.

In other words, 8 pins are input (switches) and 8 pins are output (data bus), but the output is always identical to the input*. Each input pin is simply mirrored to a corresponding output pin. Seems almost pointless, right?

*Keep reading to find out why the chip is needed and why the output actually isn't always identical to the input.

Tech note: IC46 (TC40H245) is essentially the same as the more common 74HC245, if one is looking for additional info.

What are the IC46 pins I'm checking with the logic probe and what are they supposed to do?

PIN 10 & 20 provide power and ground. IC46 wouldn't be working at all without these, so we can pretty much ignore them for probing purposes.

PIN 1 (DIRECTION) -- always high (5V)

This pin decides which side of the chip is input and which is output. In this case, pin 1 is permanently high so side "A" (pins 2~9) are input and side "B" (pins 11~18) are the output. Therefore, we can pretty much ignore this pin during probing.

PIN 19 (ENABLE) -- automatically toggles

Low (grounded) means chip can be read. High means chip is taken off the bus (output state is meaningless because the CPU is busy reading other devices). In other words, pin 19 should blink low every time the state of either the panel buttons or the music keyboard is requested. Again, this should be happening automatically and cannot be changed with any user interaction.

PINS 2~9 ("A") -- changes when keys/buttons are pressed by user

As defined by Direction (pin 1), these pins are the inputs. Unless the user presses something, nothing should be changing here. When the user presses something, the pin corresponding to that key/button must change -- probably causing the pin to "blink".

PINS 11~18 ("B") -- changes when keys/buttons are pressed by user

As defined by Direction (pin 1), these pins are the outputs. Here's where things can get confusing...

Remember when I said the outputs are just a 1:1 copy of whatever is presented to the inputs? That's mostly true, except there's that pesky Enable (pin 19) which keeps flipping on and off.

When Enable is low then that's when the CPU is attempting to read the switches, and the outputs must match the inputs (or else we'd have inaccurate readings and our buttons presses wouldn't do anything useful).

When Enable is high then the CPU is deliberately ignoring key/buttons presses because it's using the data bus to read other things instead; the outputs are technically in an unreliable state. In other words, IC46 goes brain-dead when Enable is high and the outputs don't mean a thing.

Therein lies the answer to why IC46 is used at all: The CPU doesn't want to see the key/button state all the time, so IC46 can be "offline" most of the time, and then brought back to life whenever it is time to actually check some buttons. Again, this all happens automatically, so that explains some of the blinking even when no buttons are being pressed or released.
nightcheese wrote:
Sun Sep 08, 2019 1:06 am
Without CN10 and CN6 plugged in they should all be 0 right since no key presses should be being read from the panel?
You've got the right idea. Without any input from the switches, all the inputs to IC46 should be identical and unchanging. But IC46 is connected to both the music keyboard as well as the panel buttons.

CN10 presents its button state data from the panel board. (CN6 strobes the panel board, but that's incidental here).

CN9 presents its button state data from the music keyboard. (CN8 strobes the music keyboard, but that's incidental here.

To accurately test this, both CN9 and CN10 have to be disconnected. Then please report what the logic probe tells you for each of the 20 pins for IC46. Without the keyboard or panel board connected, each individual pin should remain in the same state regardless of when you measure.

Here's what I expect to see, so let's see what differs...

PIN 1 (DIRECTION) = HIGH*
PIN 2~9 (A1~A8) = UNIFORMLY HIGH
PIN 10 (VSS) = LOW*
PIN 11~18 (B1~B8) = HIGH IMPEDANCE? POSSIBLY BLINKING?
PIN 19 (ENABLE) = BLINKING*
PIN 20 (VDD) = HIGH*

* Major red flag is these are not.

As for IC34: So long as pins 11~15 are blinking then it's probably good. It's not supposed to respond to button presses, as it's totally automated.

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Re: JX3P just plays single repeating tone and some of the buttons change it?

Post by nightcheese » Sat Sep 14, 2019 3:52 am

Thanks, that's super useful! I love how relatively simple these machines are, almost crudely simple compared to a modern computer, to the point that I feel like I could actually understand what it's doing.
Rasputin wrote:
Mon Sep 09, 2019 2:32 pm
PIN 1 (DIRECTION) = HIGH*
PIN 2~9 (A1~A8) = UNIFORMLY HIGH
PIN 10 (VSS) = LOW*
PIN 11~18 (B1~B8) = HIGH IMPEDANCE? POSSIBLY BLINKING?
PIN 19 (ENABLE) = BLINKING*
PIN 20 (VDD) = HIGH*
All the input pins are constantly high. 11-18 output pins are high with some blinking between 0 and 1. 20 is high.

19 is not blinking unless I'm reading my logic probe wrong. It has a "pulse" light which flashes, but the state stays on 1. Is this expected?

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Re: JX3P just plays single repeating tone and some of the buttons change it?

Post by meatballfulton » Sat Sep 14, 2019 1:56 pm

Nothing "crude" about that chip's enable function. It's required for any device on a shared bus.
I listened to Hatfield and the North at Rainbow. They were very wonderful and they made my heart a prisoner.

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Re: JX3P just plays single repeating tone and some of the buttons change it?

Post by Rasputin » Sat Sep 14, 2019 8:47 pm

nightcheese wrote:
Sat Sep 14, 2019 3:52 am
I love how relatively simple these machines are, almost crudely simple compared to a modern computer, to the point that I feel like I could actually understand what it's doing.

All the input pins are constantly high. 11-18 output pins are high with some blinking between 0 and 1. 20 is high.

19 is not blinking unless I'm reading my logic probe wrong. It has a "pulse" light which flashes, but the state stays on 1. Is this expected?
Yeah, gotta love the classics.

My concern here is that the "B" output does not seem to mirror the "A" input properly. If the inputs are always high then the outputs should also be high. The exception is when the Enable signal takes them offline, but *all* the outputs should be offline when this happens, so something is wrong if *all* the output pins are not behaving identically, as the input pins are (currently) in a fixed state.

In other words, each and every output should either be in a "not here" state, or exactly the same state as the inputs. The inputs are uniform, so how can the outputs not be acting as a group too? You see?

Given identical inputs, if some of outputs are behaving differently from the other outputs then that means either they are not responding to Enable at all and are permanently accessible to the bus, or they are stuck low even when the matching inputs are high. Both situations are a problem.

When you say "high with some blinking..." in regards to the outputs: Is this a consistent and predictable thing? Such as 11~15 are always high but 16, 17, or 18 sometimes going low? More details (on a pin-by-pin level) please, I think we're onto something.

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Re: JX3P just plays single repeating tone and some of the buttons change it?

Post by nightcheese » Mon Sep 16, 2019 8:12 am

Again I'm not too sure how I'm supposed to read this logic probe so this is the state of each LED on the probe for each pin:

pin | high | low | pulse
11: solid | solid | blink
12: solid | solid | blink
13: solid | solid | blink
14: solid | blink | blink
15: solid | solid | blink
16: solid | blink | solid
17: solid | solid | blink
18: solid | solid | blink
19: solid | nothing | blink
20: solid | nothing | nothing

It's predictably like this between power cycles. 14 and 16 are interesting because the 0 light blinks as well in time with the front panel LEDs. The rate of blinking on the pulse light seems to vary.

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Re: JX3P just plays single repeating tone and some of the buttons change it?

Post by Rasputin » Tue Sep 17, 2019 6:33 am

nightcheese wrote:
Mon Sep 16, 2019 8:12 am
It's predictably like this between power cycles. 14 and 16 are interesting because the 0 light blinks as well in time with the front panel LEDs. The rate of blinking on the pulse light seems to vary.
It occurred to me that measuring the output side of IC46 isn't going to work well because you're essentially just measuring data bus activity on anything else that happens to also be enabled. If the JX3P appears to be registering keyboard/keypress data even with all four of the keyboard/panel connectors disconnected then it seems as if there is activity on the bus even when only IC46 is supposed to be active.

You'd probably have to start selectively disabling things on the bus to figure out what's wrong, and that's just too much to tackle.

My guess is that either the outputs of IC46 are bad and causing phantom key/button presses when IC46 gets its chance on the data bus, or IC46 is actually fine but there is bus contention because there is a problem with one of the enable signals (IC41?) which is making another device active when only IC46 is supposed to be active.

Unfortunately, I'm out of practical ways to test any further, at least for the moment.

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