How to check if Top Octave Generator chip is working

[lucky.peic]

Hello, i have old Eko new tiger duo organ that no does not produce sound from keys (drum machine rythms still produce drum sounds so amp is working)

According to schematics TOG chip creates square wave frequency then signal goes to dividers and signal distributor chips and then into keyboad and then into filters and preamp board (if you turn on effects and switches for other sounds then it goes trough some other circuts instade of directly to amp but im currently tracing it to amp)

Basicly i want to know how to confirm that this chip is outputing tone that it is supposed to generate, i do not have osciloscope
can i just put resistor on cheap ebay 3 watt amp (i dont care if i ruin cheap amp from ebay) and try to connect it to one of output pins on TOG

Should i be able to hear that square wave frequency it generates to confirm it works if i do that

If not what is best way to check if that chip is working without using osciloscope

Im thinking of uploading schematics if that can help you to help me diagnose the problem here but i am kind of afraid that im gonna get into trouble with copyright if i upload schematics and service manuals as i had to pay to get them so i dont know if they are copyrighted.....

[Drawbar Dave]

Have you got a multimeter? If so you can at least check that the correct voltage is reaching the ic. Have you reflowed solder joints too?

[geoelectro]

What I do is find a place in the organ circuit that when you touch it, you hear hum. Like a preamp circuit. Then, with your finger on that spot, take you're other hand and with a small screwdriver or similar touch the output pins of the TOS. You should clearly hear the tones if they are working.

geo

i guess I should add not to do this with tube circuits...😳

[KC9UDX]

In my experience, this is safer for the amp under test if it has tubes. Tubes don't get zapped by static or ground noise. They are also much more responsive to injected signals. Of course, it's important to know where the grids are and where the plates are. But this kind of familiarity is necessary for working on anything. You wouldn't want to mistake a fuel line on an engine for a vacuum line!

[lucky.peic]

Have you got a multimeter? If so you can at least check that the correct voltage is reaching the ic. Have you reflowed solder joints too?

Yes, i have checked and IC is getting its 12 volts, i have also reflowed some solder joints but not all of them so far

[lucky.peic]

What I do is find a place in the organ circuit that when you touch it, you hear hum. Like a preamp circuit. Then, with your finger on that spot, take you're other hand and with a small screwdriver or similar touch the output pins of the TOS. You should clearly hear the tones if they are working.

geo

i guess I should add not to do this with tube circuits...😳

I tried that and i cant hear anything but that might be due to AMP, i know i said in first post that amp is working but i was wrong, its only partially working it is verry quiet and i can only hear drum machine working if i put my ear on speaker so amp probably needs recap..... it will probably take a month for caps to arrive so for now i am using small ebay 3w amp and 3w speaker that i sodered aligator clips on with resistor so i can tap into the signal

When i tap into the signal from from wire that goes to amp input pin i can hear drum machine loud and clear trough my diy signal tracer but still no sound from keys.....

[lucky.peic]

Oh i almost forgot, i noticed interesting problem

So wires that go from outputs of top octave generator should carry frequency to dividers but for some reason when pressing keys on keyboard the keyboard actually sends some voltage in rage of 2-5v to outputs of tog, is it supposed to do that or what is happening, im tottaly confused

It should be sending signal from those pins and not recive voltage to them when pressing keys, wired......

Also when i turn on tremolo i get verry loud buzzing from my signal tracer and from internal speakers (its quieter on internal speakers because apperently amp needs new caps)

So far only sounds i got out of this organ is drum machine and tremolo buzzing like crazy

I will probably upload a short video tomorrow showing problems i have found since my english isnt the best so video might explain it better

Just let me know if you want me to upload service manuals (its 16 pages and has all diagrams schematics and IC pinouts) if that might make it easier to help me diagnose the problem

This old combo organ was my dads and i really want to keep it and fix it but its my first time fixing organ and im not really experienced so any help i can get here is really appriciated

I am currently putting back keys, i spent most of the day cleaning everything and removing keys to clean them so i will post photo of organ later :)

[lucky.peic]

Here is picture of organ

Bottom keyboard is still missing all white keys because i have to clean them first

[Thesweetwaterkid]

You can make an audio probe from a guitar(or similar) cable. Solder an alligator clip to the ground wire and something small enough to poke around the chips pins onto the positive wire. Connect the clip to ground and use the other part to find the signal. Has to be plugged into an amp of course. I use this to fix broken effects pedals and to listen to different parts of circuits on toys when I am circuit bending. Cheap and easy to make.

[David Anderson]

I can't imagine trying to do Combo Organ repairs without a scope. You can easily buy an older scope that would work just fine at these low frequencies for very little money. I think I paid $75 for the scope I've been using for the past 20 years. It won't have all the bells and whistles of newer scopes, but you don't need those features for this kind of work.

[lucky.peic]

You can make an audio probe from a guitar(or similar) cable. Solder an alligator clip to the ground wire and something small enough to poke around the chips pins onto the positive wire. Connect the clip to ground and use the other part to find the signal. Has to be plugged into an amp of course. I use this to fix broken effects pedals and to listen to different parts of circuits on toys when I am circuit bending. Cheap and easy to make.

I did that but used small cheap ebay 3 watt amp instade of guitar amp and it worked for signal tracing, first ssignal i found was drums sounds from drum machine in organ then i tried tracing keyboard sound signal and i even tried probing generator chip but it only produced high pitch unclean literraly garbage sound on all of it pins and it made even wierder sounds when i turned on vibrato so it was now outputing at least something but it seems like something on tone generator board is bad

Tone generator board has 3 ICs, one is tone generator and other is vibrato chip and 3rd one is small voltage regulator that has same package as transistor

Definitley something dead on tone generator board bcause after few hours of trying to find cause i turned the organ off and next time i turned them on now tone generator wont even output that garbage sounds and frequencys that it outputed before and one of transistors is so hot to touch that i screamed when i touched it


I also found another wierd issue

So in this organ preamp and filters for upper keyboard are on the same board (this model of organ has every module seperate, all boards are speprate and removeable without desoldering and they almost look like old PCI cards in computers) so basicly all sounds (drum machine, upper keyboard and lower keyboard and all other boards that produce sounds) go to seperate inputs on preamp board but for some reason preamp board is outputing exacly 6.11 volts on each INPUT so there is something wrong with both preamp and tone generator

Any ideas about that wierd voltages on preamp inputs, it certanly does not seem right......

[lucky.peic]

I can't imagine trying to do Combo Organ repairs without a scope. You can easily buy an older scope that would work just fine at these low frequencies for very little money. I think I paid $75 for the scope I've been using for the past 20 years. It won't have all the bells and whistles of newer scopes, but you don't need those features for this kind of work.

I am saving up for some more modern scope currently so i would like to avoid wasting money on buying something older now for this one repair, i do this only as hobby to try and fix old stuff i have from my family

But anyway, i managed to tap into tone generator signal using small amp and i was able to hear some frequency on its pins but it sounded broken and wrong and after few hours of troubleshooting i turned organ off and few hours later i turned it back on and now that same tone generator wasnt producing any sound anymore and one transistor is awfully hot

There are 3 ICs on that tone genreator board, its tone generator chip, vibrato chip and voltage regulator that is connected to vibrato ic


Also it seems there is something wrong with preamp board, it has one output that goes to amp and multiple inputs (for both upper and lower keyboard and for drum machine and other effects boards like tremolo board) but the issue with preamp board is that it is for some reason producing 6.11 volts on each of its INPUTS expect for drum machine input

What could be causing it and could that have killed tone generator IC?

[Drawbar Dave]

I can't imagine trying to do Combo Organ repairs without a scope. You can easily buy an older scope that would work just fine at these low frequencies for very little money. I think I paid $75 for the scope I've been using for the past 20 years. It won't have all the bells and whistles of newer scopes, but you don't need those features for this kind of work.

That's what I did for my Duo.

[David Anderson]

Also it seems there is something wrong with preamp board, it has one output that goes to amp and multiple inputs (for both upper and lower keyboard and for drum machine and other effects boards like tremolo board) but the issue with preamp board is that it is for some reason producing 6.11 volts on each of its INPUTS expect for drum machine input

What could be causing it and could that have killed tone generator IC?

I'm not familiar with the circuit, but when I find voltages that shouldn't be there in solid-state circuits, I would usually suspect a shorted capacitor or a shorted transistor. It's harder to track problems in solid-state circuits because there's less input/output isolation.