Sequential Drumtraks tuning problem

[crochambeau]

I took down a list of parts you have replaced, I notice in your first post you typed U216 twice in the first declaration of work done. Typo? Or is there another part that has been reworked?

I got sick of looking at split pages on the schematic; here's a marked up pages B and C. Apologies if you're colorblind, I can use a different method if need be.





AFAIK, you have replaced everything in red, I'm ignoring sheet A (U101) as I don't think it germane at the moment.

On page C we observe U226 DAC (replaced) feeding an analog voltage to U232 and U228 (yellow and blue respectively). I believe that analog voltage should move around in relation to a logic address coming from U218. This address will consist of 3 lines of "high/low" being fed to pins 9, 10, and 11 of BOTH U232 and U228 - this determines which instrument is being affected.

Also from U218 pin 5, and U218 pin 10 is going to be a "high/low" logic state that will instruct those ICs (U232 and U228) to either listen to, or ignore, what 3 line address is being broadcast to pins 9,10, and 11.

I would start by observing the analog voltage (for all we know, the U230 op-amp could be the issue) and then move on to watching for the logic states (I think to be effective at the logic side, you'll need to be measuring multiple spots at once)

[crochambeau]

Volume, I believe, is a product of voltage level on pin 11 of the 6070

I've got 00V on all 6070's pin 11.

The level instruction might be fast, or a pulse. I don't know. At the moment let's ignore the 6070 as possible culprit, because it seems like the issue is across both volume and tune, which really makes me think shared parts across both systems, of which there are many.

[cutoffres]

I took down a list of parts you have replaced, I notice in your first post you typed U216 twice in the first declaration of work done. Typo? Or is there another part that has been reworked?

Yes, i've also replaced U218.

I've just replaced U230 AOP without success ( there where no strange measures but the ic was very hot).

Is the 100pf capacitor between u230 pin 1 and U226 pin 16 could cause that kind of problem?

[cutoffres]

Also checked all data bus line, they are all the same on ech IC of the Data Bus. I still feel that U230 is very hot.
What kind of measure do you have on your machine on U226 and U230?
Here is what i measure:
U226 DAC:
Pin 1= two 4V Pulses Pin 6= 4VPP Data line Pin 11= 4VPP Data line Pin 16= 800mvPP at 4V
Pin 2= Nothing Pin 7= 4VPP Data line Pin 12= Nothing
Pin 3= Nothing Pin 8= 4VPP Data line Pin 13= 1us Pulse
Pin 4= Nothing Pin 9= 4VPP Data line Pin 14= +5V
Pin 5= 4VPP Data line Pin 10= 4VPP Data line Pin 15= -5V

U230 OP Amp:
Pin 1= 800mvPP Pulse at 4V Pin 5= -5V
Pin 2= 2VPP 50us pulses at 4V Pin 6= -5V
Pin 3= Nothing Pin 7= -5V
Pin 4= -15V Pin 8= +15V

Do you find that measurements ok comparing to your machine?

[crochambeau]

Also checked all data bus line, they are all the same on ech IC of the Data Bus. I still feel that U230 is very hot.
What kind of measure do you have on your machine on U226 and U230?
Here is what i measure:
U226 DAC:
Pin 1= two 4V Pulses Pin 6= 4VPP Data line Pin 11= 4VPP Data line Pin 16= 800mvPP at 4V
Pin 2= Nothing Pin 7= 4VPP Data line Pin 12= Nothing
Pin 3= Nothing Pin 8= 4VPP Data line Pin 13= 1us Pulse
Pin 4= Nothing Pin 9= 4VPP Data line Pin 14= +5V
Pin 5= 4VPP Data line Pin 10= 4VPP Data line Pin 15= -5V

U230 OP Amp:
Pin 1= 800mvPP Pulse at 4V Pin 5= -5V
Pin 2= 2VPP 50us pulses at 4V Pin 6= -5V
Pin 3= Nothing Pin 7= -5V
Pin 4= -15V Pin 8= +15V

Do you find that measurements ok comparing to your machine?

My negative rail issue has yet to be resolved (I buy parts in bulk to keep the cost down, so that part is waiting on a larger order) so my readings of U230 are probably going to be wrong.

U226:
1 = 2 volt DC, no pulses
2 = no signal
3 = no signal
4 = data line, roughly 4.5 volt PP
5 = data line, roughly 4.5 volt PP
6 = data line, roughly 4.5 volt PP
7 = data line, roughly 4.5 volt PP
8 = data line, roughly 4.5 volt PP
9 = data line, roughly 4.5 volt PP
10 = data line, roughly 4.5 volt PP
11 = data line, roughly 4.5 volt PP
12 = no signal
13 = ~1 us pulse, negative going on roughly 4 volts DC
14 = VDD (4.92 volts)
15 = 2 volt DC (this is connected to the output of U230)
16 = 2 volt DC (this is connected to the output of U230)

I felt my U230, and - keeping in mind my negative rail is dead and that part might not be conducting at all, it was stone cold.

I feel like there is a very low chance that part would be running hot to the touch if everything was operating normally, that part is rated at 25 mA per channel output. Replacing that dual opamp might be the trick.

I read data on U226-4, and the schematic corroborates that as a data line. Might be something to double check.

[cutoffres]

I feel like there is a very low chance that part would be running hot to the touch if everything was operating normally, that part is rated at 25 mA per channel output. Replacing that dual opamp might be the trick.

I read data on U226-4, and the schematic corroborates that as a data line. Might be something to double check.

Unfortunately i had made a mistake, and my readings on U226-4 are the same like you, i'v got data line too on pin 4.

I've allready replaced U230 by a TL072 i had, unfortunately it still doesn't solve the problem and the TL072 is even more hot than the 1458. The problem must be somewhere around the U230 Circuitry.

I understand that your negative rail issue hasn't been solved and may make the result differs.
However this this the correct measurement i make on U230:
Pin 1: 800mv pulse at 4V
Pin 2: 2vpp 50us Pulses at 4V
Pin 3: Nothing
Pin 4: -15V
Pin 5: -5V
Pin 6: -5V
Pin 7: -5V
Pin 8: +15V

[cutoffres]

Crochambeau, did you finnaly repaired your machine? Is it possible you measure U230 pins?
I'am a bit lost now.

[crochambeau]

Crochambeau, did you finnaly repaired your machine? Is it possible you measure U230 pins?
I'am a bit lost now.

No, I should cut my Mouser order in the next couple of days though, I'll squeak this one in ASAP and update.

That said, I'm a firm believer that your dual opamp should be cool to the touch.

[crochambeau]

Parts arrived today!

My issue turned out being a popped tantalum right after the negative regulator (and not the regulator itself).

Pins of U230 measure out as follows:

Pin 1: waveshape, picture attached.
Pin 2: common/no voltage
Pin 3: common/no voltage
Pin 4: -15 volts (yay!)
Pin 5: -5 volts
Pin 6: -5 volts
Pin 7: -5 volts
Pin 8: +15 volts



Furthermore - no perceptible heat to the touch after warm up on U230.

I hope this is helpful? My machine is back up and running, so I can make more non-invasive measurements if need be. Good luck!

[cutoffres]

Pins of U230 measure out as follows:

Pin 1: waveshape, picture attached.
Pin 2: common/no voltage
Pin 3: common/no voltage
Pin 4: -15 volts (yay!)
Pin 5: -5 volts
Pin 6: -5 volts
Pin 7: -5 volts
Pin 8: +15 volts

Ok thanks a lot i'have double checked and here is what i measure:

Pin 1: waveshape (not the same but similar to yours, certainly due to the fault)
Pin 2: 2VPP waveform at +5V
Pin 3: common/no voltage
Pin 4: -15 volts
Pin 5: -5 volts
Pin 6: -5 volts but but with a 6vpp sinewave!
Pin 7: -5 volts but but with a 6vpp sinewave!
Pin 8: +15 volts

So we should be clause the problem. Apart the Diode between pin 2 and pin 3 and the 100pf capacitor between pin 1 and pin 2 i don't see much suspects here?
I'm going to double-check immediately solder joints, replace the diode and will order a 100pf on my next order.
If my new measures give you an idea let me know

Also i don't understand how works the Vref on the DAC would it a fault on the voltage that enters in the DAC?

[crochambeau]

Also i don't understand how works the Vref on the DAC would it a fault on the voltage that enters in the DAC?

According to the AD7524 datasheet absolute maximum voltage allowed on VREF pin 15 is +/- 25 volts.



Looking at the block diagram of the IC, it appears that VREF simply feeds a resistor ladder that gets switched - so it is fairly insulated from the +5 volt logic that drives the IC.



I would speculate that I was reading nothing on U230 pin 2 because my machine was not producing sound at the time of measurement.

What is the general frequency of your 6VPP sine wave you're seeing on U230 6&7? Does it match the signal seen on U230 pin 2?

I don't have my machine open at the moment, but I wonder if the difference in symbol between U226 12&3 GND reference and U230 pin 3 GND reference is meaningful in any way. I'm quite literally grasping at straws there..

I would expect failure of the 1N914 or 100 pF cap at U230 pin 2 could be very detrimental to the signal introduced to U226 pin 16 (RFB), which I suppose could spill out the VREF pin, but the levels do not make complete sense to me.

Were this my project, I would pull U230 and measure/look at pins of U226, to see if the oscillation is there, or if it is coming from the U230. Then I would either breadboard a U230 copy and hook up one section at a time and repeat measurements, or I would chase the oscillation up stream.

[cutoffres]

What is the general frequency of your 6VPP sine wave you're seeing on U230 6&7? Does it match the signal seen on U230 pin 2?

The sine is 840khz at start and slowly speed down. No it do not match the signal seen on U230 pin 2.

I would expect failure of the 1N914 or 100 pF cap at U230 pin 2 could be very detrimental to the signal introduced to U226 pin 16 (RFB), which I suppose could spill out the VREF pin, but the levels do not make complete sense to me.

I've replaced the diode and the 100pf cap without success.

Were this my project, I would pull U230 and measure/look at pins of U226, to see if the oscillation is there, or if it is coming from the U230. Then I would either breadboard a U230 copy and hook up one section at a time and repeat measurements, or I would chase the oscillation up stream.

I've put U230 on a socket so i'm able to measure pins i will do it very soon and will let you know. Thanks a lot crochambeau, you help me a lot.