Juno D synthesizer gets stuck on start up.

[Yamin]

Hi guys, I've got a roland Juno-D keyboard in for repair. What had happen was the owner went to turn on the keyboard and the front panel flashed on for a moment and the unit turned off with a burn smell.
Someone before me had a look at it and gave up. I have found the burned component which was the IR led (LED44) which is used for the D-beam. I checked all the components in its path and everything was okay. The tech who checked before me had removed IC8 which is an opamp. So I have replaced it with a new one.
What happens now
When the unit is turned on, the LCD lights up with dark block characters. No leds on the front panel lights up and the keyboard just gets stuck at startup. Sometimes the leds flickers on for a moment and then turns off.
I have checked all the power rails. The 5V and 3.3V rails are good. However the +9V rail shows 7.7V! and -9V rail shows -8.5V (which is in the limit stated on the inverter datasheet). There is no change with the 7.7V even when I disconnected all the other boards which needs the +9V.
I checked the crystals outputs and it shows clean sine waves. The things I check all seems to be ok, and I cant figure out what it could be. I thought that the microprocessors were not resetting on start up so I tried manually resetting it. No difference everything initializes and then gets stuck.
Potential breakthrough
I tired chasing the problem of the leds not coming on - I scoped IC6 which is a D-flip flop, the clock signal was there and all the inputs had square waves, but there were no outputs. A square wave does appear the moment the led flickers.
This is a problem right? But I still cant think why this could be a problem to cause the whole unit to freeze up.
I want to figure out what else could be causing this problem before ordering the flip flop.
Your help is greatly appreciated.
This is the link for the service manual electronica-pt.com/esquema/audio/roland-rs50-14976/   , I tried uploading it here but it exceeds the upload limit here.  The circuit diagrams starts from page 31.

[ozcar]

So you think it might have locked up when  LED44 happened to be turned on and the 100% duty cycle killed it?

7.7V does sound too low. So what voltage are you getting out of the adapter and say at the input of IC3?

Dark blocks on those displays is typically what you get if power is applied, but it receives no commands to initialise it. You'd expect that to be one of the first things done by the processor, so I'd wonder if the processor was running at all. However, if the processor was not running, there would be no activity driving the LEDs or trying to scan the switches, which it seems you do have. Does the LCD enable ever go high, and is there any activity on the LCD data lines and RS?

I assume “no outputs” from IC6 means they are all low? Might not be a problem there unless you know for sure that some of the inputs were high when it was clocked.

[Yamin]

@

So you think it might have locked up when  LED44 happened to be turned on and the 100% duty cycle killed it?

That's a possibility, it was definitely burned and was quite hot when I touched it. I have replaced it with a normal led until I get an IR LED. The normal led doesn't light up either.

7.7V does sound too low. So what voltage are you getting out of the adapter and say at the input of IC3?

The adapter output is around 9.20V, I get something around 8.7V at the input of IC3 (5V voltage regulator). There is a series voltage regulator for the 9V rail on the main board(Q17 page 37). I have replaced the electrolytic caps connected to it. Still the output is 7.7V with and with out the other boards connected, it looks that the 9V rails are needed for the other boards mainly.

Dark blocks on those displays is typically what you get if power is applied, but it receives no commands to initialise it. You'd expect that to be one of the first things done by the processor, so I'd wonder if the processor was running at all. However, if the processor was not running, there would be no activity driving the LEDs or trying to scan the switches, which it seems you do have. Does the LCD enable ever go high, and is there any activity on the LCD data lines and RS?

I assume “no outputs” from IC6 means they are all low? Might not be a problem there unless you know for sure that some of the inputs were high when it was clocked.

I would have to probe the LCD data lines. At one point I gave up thinking that the processor was dead. But then I probed IC6 which is the D-flip flop used for the leds, there were activity on all the input pins all the time, clock signal was present. But all the outputs were held low. Occasionally if the leds flickered it showed some activity but only for that brief moment.

Any idea on what I should further?

Thanks so much for the help. Really do appreciate it.

[ozcar]

You have to understand I'm not familiar with this device at all, the only Roland box I have tangled with was a MKS7 which is a very different thing.

I see that Q17 is not a regulator as such, it is a capacitance multiplier (the “ripple filter” in the block diagram), and there is going to be some drop across that, so when they say “9V” for the output there I think they may be exaggerating a bit!

Somehow the processor seems to be alive, but not quite. If you can find why there is nothing on the LCD I think you will have made a big step forward. I see there is even an LCD test routine - if only you could get something on the LCD in the first place.

At first I thought the LCD was one of those very common HD44780/KS0076/etc modules. Well, it looks very similar, but the connections seem to be a bit different. Another reason why you might only get blocks on the display could be that the LCD operating voltage is too far out. Often there is a “contrast” preset to adjust this, but here the voltage, V5 or LCDV5,  appears to be under control of the processor via PWM. So maybe check the LCDPWM signal from the processor and what is going on around Q5 to LCDV5.

I still don't know whether there is a definite problem with IC6. The LSD0-LSD7 lines are also involved in scanning the switches, and I thought perhaps you could be seeing signals there relating to that rather than driving the LEDs, However, looking at it again, maybe those lines are only used as inputs to the processor for scanning the switches. The real indicator is still whether you see any of those lines high when you see the clock for IC6, but the corresponding output stays low, and I'm not sure from what you said if you actually saw that.

Another clue that the processor is alive would be if you see anything happening on the outputs of IC5 (scanning switch rows).

[Yamin]

Thanks ozcar,
'Capacitance multiplier' that's something new to me. Gonna do some reading on that, I thought it looked very odd for a voltage regulator hehehehe.

Weird thing about LCDPWM, Q5 is not there! its missing. However the owner did confirm that he was able to change the contrast setting while it was working. :S

I still don't know whether there is a definite problem with IC6. The LSD0-LSD7 lines are also involved in scanning the switches, and I thought perhaps you could be seeing signals there relating to that rather than driving the LEDs, However, looking at it again, maybe those lines are only used as inputs to the processor for scanning the switches. The real indicator is still whether you see any of those lines high when you see the clock for IC6, but the corresponding output stays low, and I'm not sure from what you said if you actually saw that.

Another clue that the processor is alive would be if you see anything happening on the outputs of IC5 (scanning switch rows).

LSD0-LSD7 definitely had action on those lines, square wave pulses. But there were no output or intermittent output from IC6. I did probe IC5 but I can't remember the results I got. I shall do it again.

Could this be a possibility, its a bit far fetched but just a thought in my head - you know when these kind of unit turns on, there is this initializing processes where  all the leds turn on and the lcd turns on. Could it be possible that the initialization process is not complete due to a hardware issue (like the IC6 not working properly or something like that), rather than a software issue. It seems that the unit is stuck at initialization process. I say this because during the rare and intermittent output from IC6 all the leds try to glow. This is not normal when the unit is being used.

Does the initialization process do a check/test of some sort?

Again thanks so much for the help. I shall get back with further results I get. I really do want this project to work, or at least be definite about what the problem is.

[ozcar]

I don't see any obvious way that the processor would know the outputs of IC6 don't go high when they are supposed to (if that really is happening).

Are the blocks on the display only on the top line, or on both lines? I think those LCD controllers power up with 1 line display by default, and would have to receive a command to set it to 2 lines. So, if you have only one line of blocks it would be a sign that the LCD received no initialisation commands, rather than the contrast is just totally wrong.

[Yamin]

Are the blocks on the display only on the top line, or on both lines? I think those LCD controllers power up with 1 line display by default, and would have to receive a command to set it to 2 lines. So, if you have only one line of blocks it would be a sign that the LCD received no initialisation commands, rather than the contrast is just totally wrong.

The blocks are on both the lines! Could it be the missing Q5 setting the contrast totally wrong?

[Kjelt]

Not sure if it is related but I heard many synths from the 80's start having degraded program memory (eprom or otprom), you are sure the uC is working correctly ?

[ozcar]

Is the circuit generating LCDV5 different to the diagram, or is Q5 just missing? If the latter then you'd expect LCDV5 to be zero, and certainly not adjustable. Is there a signal on LCDPWM?

[Yamin]

Not sure if it is related but I heard many synths from the 80's start having degraded program memory (eprom or otprom), you are sure the uC is working correctly ?

Thanks Kjelt, how can I confirm that the micro controller is not working. It appears to be partly working so its a bit hehehehehe

[Yamin]

I shall check it, I'm on my way to the workshop. If I remember correctly all the other components related to it were there, and the owner did confirm that he was able to adjust the contrast. I figured that there might have been some other means of adjusting the contrast.

[Yamin]

Is the circuit generating LCDV5 different to the diagram, or is Q5 just missing? If the latter then you'd expect LCDV5 to be zero, and certainly not adjustable. Is there a signal on LCDPWM?

Yes LCDV5 is 0V. I haven't got access to the scope now so I cannot it probe right now. I measured pin 5 (lcdpwm) of IC18 with the DMM - I get 5V there
I have included a picture of the missing Q5, as you can see some other components related to is there! like R53

[Kjelt]

Thanks Kjelt, how can I confirm that the micro controller is not working. It appears to be partly working so its a bit hehehehehe

Depends on the program memory if it is external like an eprom and it is a normal one you can read it out in your epromprogrammer.
What I sometimes do then is first make a backup on another eprom and verify the device behaviour is the same.
Then read it out with Vcc+5% and Vcc-5% (some people use +/-10% but I find that to much to the edge) and compare the three files.
If they are binary equal then you have a high chance the code is still correct.
If not you get to guess which is the right one but at least you know there is an issue. If the number of differences is small you can probably figure it out.