Is it possible to know just from the pins descriptions bellow (attached image) what results I should expect from a logic probe?

In terms of low, high or pulse? In order to diagnose if the IC is working?

 

Not enough information. What chip is it? What are the inputs? Outputs will depend on inputs and the operation of the chip.

And some pins you might need a scope not a logic probe. For example SOOT. Or if it is a running systems with inputs constantly changing then a logic probe will be of little use. You would need a logic analyzer.

 

Not enough information. What chip is it? What are the inputs? Outputs will depend on inputs and the operation of the chip.

And some pins you might need a scope not a logic probe. For example SOOT. Or if it is a running systems with inputs constantly changing then a logic probe will be of little use. You would need a logic analyzer.

It is the chorus IC 8 in the centre. That is all I got. It is for an old keyboard and they don't make spare parts or ICs for it anymore.

 

That is a very long shot in the dark.
You need to diagnose the problem based on functionality.

Start off with what is working and what isn't working.
What do you know so far after you turn on the power switch?

 

It is the chorus IC 8 in the centre. That is all I got. It is for an old keyboard and they don't make spare parts or ICs for it anymore.

View attachment 166265

From the enormous number of pins, I am assuming all of the chips are surface mounted. If you don't have the skills to replacesomething like that )most people don't) then it isn't even worth messing with. And if you can't get spare parts on top of that. Time for a new keyboard.

 

That is a very long shot in the dark.
You need to diagnose the problem based on functionality.

Start off with what is working and what isn't working.
What do you know so far after you turn on the power switch?

When chorus effect is enabled for a sound the sound starts cracking and failing. If you turn the chorus off then sound is clear and fine.

Everything works fine but the chorus. Reverb, D/A, etc... and I believe that eliminates most of the PCB and ICs.
All chorus and chorus RAM PCB traces are ok. I got no PCB issue. Chorus receives it's +5v ok as well. All capacitors have been replaced.

Which points out to either the chorus IC or chorus RAM IC. But now I got to find a way to diagnose which on these ICs are failing and where, how.

I am not an expert but if you point the right direction I will follow.

 

From the enormous number of pins, I am assuming all of the chips are surface mounted. If you don't have the skills to replace something like that )most people don't) then it isn't even worth messing with. And if you can't get spare parts on top of that. Time for a new keyboard.

Yes, surfaced mounted. I do have the proper equipment and can easily remove and put back this type of IC without causing any damage. And have done that already to check traces, pins, clean PBC and IC, checked pads and pins on microscope, etc... so far from the outside it is all good.

As I am learning I just need to be pointed on the right direction on what I should learn in order to understand better what is going on signal wise with these ICs.

 

As I mentioned above. You likely aren't going to do this with a logic probe. Signals are moving way to fast.

I don't understand how you can have the equipment and skills to replace chips like this but don't have the equipment or skills to troubleshoot. Replacing chips like this is an advanced skill that most hobbyists do not possess.

 

As you suspected, it would appear that the problem is related to IC7 or IC8.

The only procedure for moving forward that I can think of at the moment is to use a logic analyzer (not as simple as a logic probe) to test the address and data buses.

The other thing that would help is to compare the signals against a working keyboard.

 

As I mentioned above. You likely aren't going to do this with a logic probe. Signals are moving way to fast.

I don't understand how you can have the equipment and skills to replace chips like this but don't have the equipment or skills to troubleshoot. Replacing chips like this is an advanced skill that most hobbyists do not possess.

I do have good equipment, but still lack knowledge. Buying stuff is easy, hard it is to understand it. Here is an image of the IC after I removed it, cleaned everything and welded it back.

I will follow what MrChips said and try to learn more about a logic analyzer and how to use it as he suggested. If you have any suggestions I would appreciate.

 

As you suspected, it would appear that the problem is related to IC7 or IC8.

The only procedure for moving forward that I can think of at the moment is to use a logic analyzer (not as simple as a logic probe) to test the address and data buses.

The other thing that would help is to compare the signals against a working keyboard.

Thanks!!! I will follow your path!

 

Logic analyzers are not cheap. Do you have a logic analyzer? If so, what is the make and model?
Do you have an oscilloscope? If so, what is the make and model?

 

I would try resoldering the other IC involved. Fun fact, you don´t need to remove it, just re-tin all the pins.
Also check that the lines coming from other ics like clock etc. look correct.

 

Is this a Roland D-50 keyboard produced in 1987? I agree with MrChips that IC7 or IC8 is the most suspected. Is the IC7 in DIP package or in SMD?

Should not be too hard to get a 6264-150 these days. All my 6264 are all in 0.6" DIP and 62256 in SMDs...

Is there any corrosion underneath the battery? The corrosion might cause some traces to become oxidized and later opened.

Allen

 

Have you found the fault on this keyboard?

Really like to know as I sometimes got odd keyboards of Roland brand for repair.

Allen

 

Have you found the fault on this keyboard?

Really like to know as I sometimes got odd keyboards of Roland brand for repair.

Allen

Not yet. Still trying. Replaced caps, DACs, RAM, OPAmps, etc... re-soldered SMDs all you can imagine.

The chorus send data to DAC normally but I am inclined to believe the data it send is corrupted. But I have no means or knowledge to confirm that with logic scoping. I can only confirm that by changing software parameters I do reduce or increase the noise.

Tried to disable the IC by lifting CS (slave select pin 7) but as it is select LOW made no difference apart from stooping it from booting. But probing it shows it is stuck on HI (0.5v) all the time.

You can follow the thread on eevblog. I am getting to believe my chorus IC is faulty as it's surrounding components have been either replaced or checked.

If I could find a way to disabled the chorus IC without stopping the system to boot I could try stoping the IC from sending data to DAC. But so far my attempts haven't been successful.

Also has been really hard to find a replacement board.

http://www.eevblog.com/forum/repair...-fix-a-roland-d50-keyboard/new/?topicseen#new