Twin Peaks TapLFO problems

[brejna]

Hi guys, I am having a problem with this build. Tap tempo is not working and tap divison knob, also waveform is missing random function. I don't know how much these chips are sensible, but I did make mistake with orientaton of the socket and I did put chip same way. So did I burn it? 

[midwayfair]

If you fry the chip, you'd kill the whole thing, not individual functions. Reflow your solder joints first. Those ARE all digital functions, but there might be other reasons the chip isn't working properly. Whee did you get the TAPLFO?

[brejna]

If you fry the chip, you'd kill the whole thing, not individual functions. Reflow your solder joints first. Those ARE all digital functions, but there might be other reasons the chip isn't working properly. Whee did you get the TAPLFO?

It is going to be very hard to reflow joints 'cause I connected them with pins.. but I'll try that, hopefully without damaging pcb. All of other functions are ok exept those which are connected to taplfo. BTW I got chip from Thomas..

Brane

[brejna]

I have manage to separate boards and did reflow everything, but I have same problem...

[selfdestroyer]

Brejna, I got mine back and will be able to take some voltages for you tonight. Sorry I left you hanging in the PMs that were going back and forth.

Cody

[brejna]

Brejna, I got mine back and will be able to take some voltages for you tonight. Sorry I left you hanging in the PMs that were going back and forth.

Cody

Thanks Cody, I appreciate it.

[selfdestroyer]

Here is my voltages

TL074
1 4.6v
2 4.6v
3 4.6v
4 9.2v
5 4.6v
6 4.6v
7 4.6v
8 4.6v
9 4.6v
10 4.6v
11 0
12 4.1v
13 4.6v
14 4.6v

NE5532
1 1.3v
2 3.5v
3 3.4v
4 0
5 3.4v
6 3.4v
7 5.8v
8 6.9v

TAPLFO
1 5v
2 1.8v
3 1.8v
4 5v
5 0
6 0
7 0
8 5v
9 0
10 5v
11 0
12 3.8v
13 3.5v
14 0

Tap switch pad = 5v

Hope this helps some.

Cody

[HamSandwich]

Check your resistances around the problematic functions.

[brejna]

Here is my voltages

TL074
1 4.6v
2 4.6v
3 4.6v
4 9.2v
5 4.6v
6 4.6v
7 4.6v
8 4.6v
9 4.6v
10 4.6v
11 0
12 4.1v
13 4.6v
14 4.6v

NE5532
1 1.3v
2 3.5v
3 3.4v
4 0
5 3.4v
6 3.4v
7 5.8v
8 6.9v

TAPLFO
1 5v
2 1.8v
3 1.8v
4 5v
5 0
6 0
7 0
8 5v
9 0
10 5v
11 0
12 3.8v
13 3.5v
14 0

Tap switch pad = 5v

Hope this helps some.

Cody

Thanks Cody, my voltages are very close to yours and only differences were on the TAPLFO chip..

TAPLFO
1 5v
2 1.8v
3 1.8v
4 5v
5 0
6 0
7 0
8 5v
9 0
10 5v
11 0
12 3.8v
13 3.5v
14 0

Mine TAPLFO
1 4.9v
2 2.2v
3 2.3v
4 4.9v
5 0.5-4.9v
6 0
7 0.5v
8 4.9v
9 2.4v
10 4.9v
11 0
12 1.46v it depends on the shape knob
13 3.1v it depends on the rate knob
14

Any ideas?

Check your resistances around the problematic functions.

I have also checked resistors around the LFO and they are ok.

[drolo]

Do you have a frequency meter (or oscilloscope)? If you do, measure the frequency on the PWM output pin 5
Also measure the max and minimum voltages on pins 9 to 15 when turning the pots.
There might still be a chance the chip is damaged. I've had chips act weird like that.

[brejna]

Do you have a frequency meter (or oscilloscope)? If you do, measure the frequency on the PWM output pin 5
Also measure the max and minimum voltages on pins 9 to 15 when turning the pots.
There might still be a chance the chip is damaged. I've had chips act weird like that.

Unfortunately I don't have frequency meter, but will post these min and max voltage values of pins 9 to 14..
Thanks
Brane

[brejna]

Here voltages on taplfo from 9 to 14..

     Min        Max
9   0          4,91v
10  0          4,91v
11  0          3,65v
12  0          4,91v
13  0          4,91v
14  0             0v

[drolo]

Hmmm ... the voltages look correct. Does pin 4 go low when you press the tap switch ?

[brejna]

Hmmm ... the voltages look correct. Does pin 4 go low when you press the tap switch ?

Yes it does.

[drolo]

So it seems everything around the chip is fine, the voltages seem correct.
It could be the chip, but it's hard to say with certainty.

I once had a similar issue where in the end there was something weird going on with either either the 22p caps or the oscillator as I was having an unstable frequency on the PWM output.
I had no tap function and between 2 shape positions I would get a very random signal. like the chip was outputting only noise instead of an actual PWM.
But I never really was able to find out because I desoldered so much around the caps and crystal that in the end I lifted a pad and decided to build a new one from scratch. It could also have been bad continuity from the IC socket. Hard to tell. In that particular case it had not been the chip as I was able to use it on the new build.

Thats why I was asking about the possibility to read the frequency on the PWM output. It should be 19.5KHz when it's clocked right and working properly.

Check perhaps around those 2 caps and the crystal if the connections are good or if there are no solder bridges.