Digital Piano repair help.

Thread Starter

SteveHow

Joined Jul 2, 2012
80
You are reading my notes correct. AFTER I had shorted (Or assuming I had).....

.........."I then went back to IC48 Pins 1/2 and sure enough it was back to its initial state, however this time I was able to read the frequency at 200KHz. (This was a clean Square Wave with the Highs and Lows of equal duration)"

I am going to keep hunting. I personally feel that IC48 is still a working unit. Unfortunately, I will never know if that little slip has made things worse, or we are just seeing the intermittent behavior of the fault.

No hurry, I know you have a life. This is a huge project and honestly its giving me a headache. However I am not ready to give up yet.

Cheers
Steve
 

MrChips

Joined Oct 2, 2009
30,720
Ok, good to know that we have a signal at A15.
Let me know if there is any activity on the DATA lines.
Frequency or pulse widths are not important. I need to know that they are changing.

After that I need you to look at IC45 all pins.
I need to know at each pin if it is LO, HI or changing.
 

Thread Starter

SteveHow

Joined Jul 2, 2012
80
No. To run the test procedures we have to get the main CPU running first.

To my question, why don't we get the 2x7 Segment LED/Front Panel working you stated above. However, I can't help but ask, why then are we not looking at the CPU? We are looking at the KPU. Surely the LED is driven by the CPU and not the KPU ?
 
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absf

Joined Dec 29, 2010
1,968
Steve said:
To my question, why don't we get the 2x7 Segment LED/Front Panel working you stated above. However, I can't help but ask, why then are we not looking at the CPU? We are looking at the KPU. Surely the LED is driven by the CPU and not the KPU ?
Today 02:03 AM
I did some tracing and found that the 3x7 seg LED is connected to CN13 & CN14 on the DM board then to IC14 LPD (Panel LED driver).

On the block diagram, the said LPD is connected to the PA Bus from KPU. The PA Bus also goes to the CPU 63C01 at P60-P67. The main job of 63C01 is to control GEW3 and GEW5 sound generators. So the actual control of the LPD is from the KPU.

I would say KPU is the Main CPU and the other CPUs are just Slave CPUs.

Allen
 

Thread Starter

SteveHow

Joined Jul 2, 2012
80
I did some tracing and found that the 3x7 seg LED is connected to CN13 & CN14 on the DM board then to IC14 LPD (Panel LED driver).

On the block diagram, the said LPD is connected to the PA Bus from KPU. The PA Bus also goes to the CPU 63C01 at P60-P67. The main job of 63C01 is to control GEW3 and GEW5 sound generators. So the actual control of the LPD is from the KPU.

I would say KPU is the Main CPU and the other CPUs are just Slave CPUs.

Allen

Well thats my first "Gotcha". I have clearly been on the wrong path.
So much for the term CPU "Central Processing Unit". In this case its not central.

Possibly also why its called IC1.

I am in two minds about whether to continue with this or graciously bow out. Clearly I know very little about whats going on and am relying on you guys for guidance. And of course I understand that you can only do so much.

To the question of whether I have or have not made things worse when I accidentally shorted IC48. All I can say is that, I did see Address 15 (IC1 A15) changing states AFTER my slip up.

Why I cannot repeat this, as its now sitting LOW, I am not sure. However I have been thinking that maybe, just maybe, I was leaning on the Keyboard and this may have put the KPU into a different state.

I guess the big question is, has the KPU died. (Even thought its clock is running)
 
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MrChips

Joined Oct 2, 2009
30,720
There you go again off on a tangent, Steve.
How about we make a deal? We keep going until we hit something we cannot fix.

So back to the troubleshooting.

What are you using for a scope probe? Maybe a photo will help.
Either remove the tip off the probe and probe directly with the pointed tip
or connect a piece of single strand hook up wire to the probe and use the wire as your probe.

Connect the grounding clip of the probe to some part of the circuit you know is GND and secure. The BLACK wire at the centre bottom appears to be GND.

Is your probe 1x or 10x?
I always use the probe in the 10x setting.

I need to know the status of all the pins on IC45, TC40H139 - Address Decoder.

Also IC10-5, IC14-40, IC15-40 are all connected and the signal is labelled \(\phi\)2M. This could be 2MHz. You can probe this at the ferrite bead

IC14-40 refers to IC 14 pin-40.

 

Thread Starter

SteveHow

Joined Jul 2, 2012
80
There you go again off on a tangent, Steve.
How about we make a deal? We keep going until we hit something we cannot fix.

So back to the troubleshooting.

What are you using for a scope probe? Maybe a photo will help.
Either remove the tip off the probe and probe directly with the pointed tip
or connect a piece of single strand hook up wire to the probe and use the wire as your probe.

Connect the grounding clip of the probe to some part of the circuit you know is GND and secure. The BLACK wire at the centre bottom appears to be GND.

Is your probe 1x or 10x?
I always use the probe in the 10x setting.

I need to know the status of all the pins on IC45, TC40H139 - Address Decoder.

Also IC10-5, IC14-40, IC15-40 are all connected and the signal is labelled \(\phi\)2M. This could be 2MHz. You can probe this at the ferrite bead

IC14-40 refers to IC 14 pin-40.

Hi Mr Chips,


I am using a 1 x 100MHz Tektronix Probe. (It has no 10x) (My Scope is 100MHz. Whats the benefit of 10 times ?

Yes I am using the Tip of the Probe, but now being super careful. I also have been using Needles for tiny stuff such as the pins on IC1.

To the results of IC45 TC40H139 Address Decoder/ Dual 2 X 4 DeMux.

Left side of IC.

1, H
2, L
3, L
4, H
5, H*
6, H*
7, H
8, GND

Right Side of IC

16, Vcc
15, L
14, L
13, L
12, L
11, H
10, H
09, H

*I thought these were originally low, when I double checked they were H again. This thing is playing tricks with my mind. Just thought I would mention this. I rebooted the Piano a few times, and they stayed High.


I will now get to the remaining ICs in your question.


Be back shortly.

Thanks
Steve



Side note, I probed connectors, GN9 and CN10 (Keyboard connector to KPU)
Measured Key press activity at both connections. Incidentally, ALL Pins on GN9 are High and go Low when a key is pressed. CN10 seems to be low and goes High but 2 different types of activity seems to be happening on CN10.


Also IC10-5, IC14-40, IC15-40 are all connected and the signal is labelled \(\phi\)2M. This could be 2MHz. You can probe this at the ferrite bead
Yes you are correct, ALL IC Pins and Ferrite was measured at 2MHz.
 
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MrChips

Joined Oct 2, 2009
30,720
You're going off on a tangent again.

I expect that if the unit is working properly all those signals would be changing constantly.
So KPU1 IC1 is stuck somehow.

If it is moving from one state to another you would expect some pins to change state while your back is turned. If any output pin changes state then some input pins would have changed also while you weren't looking.

See if you can pick up the 4MHz signal at the XTAL CL1 that drives IC1 (grid C4).

After that look for activity on any address lines A3, A2, A1, A0 at IC6, IC7 or IC8. They are all interconnected.

How many probes do you have? If you have a total of 2 or 3 probes that would be nice.

Our focus right now is to get KPU1 (IC1) up and running. There are still a few things left to check.
 
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Thread Starter

SteveHow

Joined Jul 2, 2012
80
You're going off on a tangent again.

I expect that if the unit is working properly all those signals would be changing constantly.
So KPU1 IC1 is stuck somehow.

If it is moving from one state to another you would expect some pins to change state while your back is turned. If any output pin changes state then some input pins would have changed also while you weren't looking.

See if you can pick up the 4MHz signal at the XTAL CL1 that drives IC1 (grid C4).

After that look for activity on any address lines A3, A2, A1, A0 at IC6, IC7 or IC8. They are all interconnected.

How many probes do you have? If you have a total of 2 or 3 probes that would be nice.

Our focus right now is to get KPU1 (IC1) up and running. There are still a few things left to check.

I will try and curb my tangents :D

After that look for activity on any address lines A3, A2, A1, A0 at IC6, IC7 or IC8. They are all interconnected. NO ACTIVITY All LOW.


I have another Probe its a 400MHz 1x and 10x Tektronix. I was not sure it I could use it on my 100MHz Cro.

Yes IC1 has its clock running @ 4MHz.


Thanks
 

Thread Starter

SteveHow

Joined Jul 2, 2012
80
After I hear back from you with IC49 and IC51 we will move over to CPU IC20 and see what it is doing.

Ok, BTW, Just a reminder that there was significant ripple on +B (IC1) See post 47.


And sorry to say, I still have not found +C (see PS schematics) I will get to that also.
 

MrChips

Joined Oct 2, 2009
30,720
Ok, BTW, Just a reminder that there was significant ripple on +B (IC1) See post 47.


And sorry to say, I still have not found +C (see PS schematics) I will get to that also.
You're off on a tangent again. Let's not worry about those two for the moment.

+B is the raw DC suppy.

+C is used in the audio amp only, to control the speaker relay on power up.
 
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Thread Starter

SteveHow

Joined Jul 2, 2012
80
More stuff for you to look at.

Status of IC49 pins 1, 2, 3.
Status of IC51 pins 1, 2, 3.
Base and collector of TR4.



Status of IC49 1,2,3 (H, H, H) Respectively
Status of IC51 1,2,3 (H, H, L)
Status of IC50 1,2,3,(L, H, H) While I was at it.

I will have to find the data sheet for TR4. Unsure of the Pinouts.
 

Thread Starter

SteveHow

Joined Jul 2, 2012
80
I am having a hard time figuring out the Pinouts on TR4. I have the data sheet but something doesn't seem correct.

I will have to get back to you and your other question. I have to go do something now.

Thanks so much for you help to night. ( I must say for the first time I actually got excited, thinking you/we were getting close....)

Cheers for now.
 

absf

Joined Dec 29, 2010
1,968
Ok, BTW, Just a reminder that there was significant ripple on +B (IC1) See post 47.
Dont worry too much about +B. It was not regulated and was used for the input of comparator inside KPU1. The output of the comparator is used to create the reset signal /IC through TR5. Did you measure the voltage ? Should be around +9V, I guess.


And sorry to say, I still have not found +C (see PS schematics) I will get to that also.
+C was also not regulated. It was used for the power supply of the speaker protection circuit. It's used to protect the speaker in case the audio output chips' outputs are non-zero.

Allen
 

MrChips

Joined Oct 2, 2009
30,720
Just looking ahead. Here is my prognosis.
Voltage at TR4 collector at 5V is ok.

We are back to looking for activity at address A15 at IC48 pin-1 immediately after power ON.
If A15 is never HIGH, always stuck LOW then IC1 is toast. Game over.
If it ever goes HIGH then there is still some hope.
 

absf

Joined Dec 29, 2010
1,968
I am having a hard time figuring out the Pinouts on TR4. I have the data sheet but something doesn't seem correct.
TR4 is 2SC1740S.

With the part number facing you, and the leads pointing downwards. On the right is Base, middle is Collector and left is Emitter. Standard Japanese transistor pinouts.

Allen
 
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Thread Starter

SteveHow

Joined Jul 2, 2012
80
I have just emailed Yamaha in the UK, Japan, USA and Australia in the hope they may have a replacement KPU IC1.

Back tomorrow.

Thanks Mr Chips and Allen.

Cheers
Steve
 
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