Roland jet phaser debug

[Luke51411]

I just recieved a broken roland Jet Phaser. Sound passes through on all modes and the distortion/fuzz sounds really good but there is no phasing. I found this layout in the gallery as a reference for voltages

http://www.aronnelson.com/gallery/main.php/v/diyuser/AP-7+board+layout+JPEG.jpg.html
Schematic

Voltages I have are
IC1
1 -.2
2 -.1
3 0
4 9.7
5 0
6 -.3
7 -.4
8 -1.4
9 -1.35
10 0
11 -9.8
12 0
13 -1.5
14 -1.9

Ic 2
1 -.6
2 -.5
3 0
4 9.7
5 0
6 -.7
7 -.8
8 -1
9 -.9
10 0
11 -9
12 0
13 -1.1
14 -1.2

Ic3
1 -.14
2 0
3 0
4 9.7
5 0
6 0
7 0
8 -2.5~+2.5
9 1.5
10 1.5
11 -9.8
12 0
13 -4.3~+4.3
14 -5.2~

Q1 e 0 c 4.4 b .58
Q2 s 0 g 0 d ~3
Q3 e 4.3 c 9.7 b 4.9
Q4 s 0 g -1.2 d 0
Q5 s 0 g -1.2 d 0
Q6 s 0 g -1.2 d 0~1.5
Q7 s 0 g -1.2 d 0
Q8 s 0 g -1.2 d 0
Q9 s 0 g -1.2 d 0
Q10 s 0 g -1.2 d 0
Q11 s 0 g -1.2 d 0

[armdnrdy]

Shouldn't pin 8 and 13 of IC3 be the same voltage? They are connected.

It looks like the gate voltage isn't oscillating.
I have gate voltages on file of -1.49 to -1.22

I would look at the output of the LFO where it exits the switch. (wire pad 11)

Also..check the switch.

[Luke51411]

The switch checked good. I'll check the gate voltages again because I think some of them where moving a little, probably about as much as yours but I'm pretty sure some of them were static. Thanks for your help.

[Luke51411]

Wait, you mean the rotary switch? I need to check that. The fast/slow switch checked good.

[armdnrdy]

Wait, you mean the rotary switch? I need to check that. The fast/slow switch checked good.

Yes the rotary.

Look at the schematic, the LFO going to the gates is interrupted by the rotary switch. (Depth)

Since you don't have phasing in any switch position, it might be a bad connection, broken wire, ect. at the common of the switch. (where pad 11 connects to)

Edit:
Did you try adjusting the Bias trimmer?

[Luke51411]

I broke out the audio probe Here's what I have. Signal seems full at Q4 drain, Q5 drain has very faint signal, no signal at any of the JFETS after that. Ic1 pin 1 and 3 both have good signal,  pin 5 and 7 have weak signal, pin 8 has faint signal as does pin 9. Pin 11 has slightly louder signal, 13 has signal and 14 has a bit more signal. Ic 2 has NO signal anywhere except faint signal at 4 and 11. It seems the problem is happening after that first stage of phase shift.

[Luke51411]

I'm going to double check the audio probe on IC2. I'm wondering if I got the pins wrong that I'm getting signal at on that one since 4 and 11 are + and - power... It seems to me things may be pointing to IC1 having a dead amplifier stage... I suppose I should replace all of the electro caps as well.
Here is are pictures of the actual board

[Luke51411]

I audio probed again to verify my previous findings and I'm hearing audio on pins 4 and 11 of ALL three ICs but the fuzz section seems to be working properly. At pin four and 11 of ic2 I can hear the lfo ticking that ramps up and down when you activate the ramp switch. I'm still thinking there's a dead IC but now I'm wondering if that is just a symptom and something else is causing the IC to die.
Also, the drain of Q4 has signal that sounds like a narrow filter is being applied to it so I think the first stage of phase shifting is working but after that, no dice.

[armdnrdy]

Audio probe both sides of R47. (pin 1 & 6 of IC1)

I wouldn't focus on the signal on the power pins. If there is a bad IC, it could be "dumping" the audio onto the power rail internally.

Before I purchased a Jet Phaser for info purposes, I collected any board pictures I could find.
One thing that I noticed is many boards contained one different brand IC.

This leads me to believe that there is an issue that causes ICs to fail.
There are a few threads on this site with the same problem as yours.

[Luke51411]

Audio probe both sides of R47. (pin 1 & 6 of IC1)

I wouldn't focus on the signal on the power pins. If there is a bad IC, it could be "dumping" the audio onto the power rail internally.

Before I purchased a Jet Phaser for info purposes, I collected any board pictures I could find.
One thing that I noticed is many boards contained one different brand IC.

This leads me to believe that there is an issue that causes ICs to fail.
There are a few threads on this site with the same problem as yours.

Thanks, I'll focus on that area during my next debug section. It has to be a problem with one or both of these ICs.

[armdnrdy]

Before you rip out and replace any ICs....make sure R47 is good.
Check it with an ohmmeter. (multimeter)

It seems like some of the faint signal you were hearing around IC1C & D was probably back feeding through the resonance circuit.

IC2 doesn't have any signal because it's not getting past IC1B.

Now we have to find out why that is.

[Luke51411]

Before you rip out and replace any ICs....make sure R47 is good.
Check it with an ohmmeter. (multimeter)

It seems like some of the faint signal you were hearing around IC1C & D was probably back feeding through the resonance circuit.

IC2 doesn't have any signal because it's not getting past IC1B.

Now we have to find out why that is.

Yeah I guess there's no reason to assume that IC2 is bad until I'm getting signal through IC1.

[anotherjim]

I suppose that sooner or later, somebody will try to connect a battery in reverse - until they discover it won't clip on that way - which is too late as there is zero protection in the circuit.

It might well be IC1 at fault, but it's pin volts seem reasonable. There is a progressively increasing DC bias shift on the amp outputs through the phaser section, probably natural offset error since all stages are DC coupled and maybe not indicating a fault at all.

But, whatever the fets are doing, I think you should still get reasonable good signal all through the phaser section with at least unity gain out of each amp. As suggested check R47. Is there 100k between IC1 pins 1 and 6 (power off of course)?

[Luke51411]

R47 checks out, about 95k between pins 1 and 6 of ic1

[armdnrdy]

Okay...

Double check pin 1, 6, and 7 with the audio probe.

If you have a good signal at 1, a bit less at 6, and nothing at 7...IC1B is bad.

[Luke51411]

Okay...

Double check pin 1, 6, and 7 with the audio probe.

If you have a good signal at 1, a bit less at 6, and nothing at 7...IC1B is bad.

There is less signal at 7 than 6. There is still a bit there but it should be about the same as at pin 1 if the ic was functions properly correct?

[armdnrdy]

I wrote that in a bit of a hurry...I had to hop in the shower...girlfriends birthday dinner.

You should have less not "nothing" at 7 then 6.

Now check pin 2 and 1 of IC2.

If IC1B is bad, the signal should diminish as you get to the output of IC2.

The signal isn't amplified through IC1B...it's travelling through 100K resistors.

[Luke51411]

Now I don't know anymore... I turned the volume up on the amp and there is signal where there should be on IC2 it's just very quiet It gets progressively quieter through IC2 and gets louder again when it comes back through IC1 and I traced the signal from there through the rest of the components up to the rotary switch and there is signal there. Ok now... Maybe it's not an IC issue... Could it be something with the JFETS? As the LFO seems to be working and the signal is getting through the ICs. I did at one point rotate the trimmer back and forth to see if that was the problem and it didn't seem to do anything.

[Fender3D]

What about C17?

[Luke51411]

What about C17?

What about it? How can I check it? I can't really audio probe it with it going to ground can I? It says tantalum on that layout but I think it might actually be an aluminum electro on the original. Replacing the electro caps is on my list of things to do I was just hoping to narrow down what the problem is. Would it be worth looking at the zener diode? Maybe that is fried and not allowing the trimmer to bias properly?

Thanks for your help guys, I'm not great at troubleshooting yet and I feel like I'm learning a lot already on this project.