Fender Roc Pro 1000 - Output is SUPER low

[nickb]

In that case Q7 is bad and I bet Q6 is also a gonner. Time to replace them. This would be a good time to update your profile with your location so we know who to direct you to for the parts.

[slow6i]

In that case Q7 is bad and I bet Q6 is also a gonner. Time to replace them. This would be a good time to update your profile with your location so we know who to direct you to for the parts.

Location is updated. If you think that they are both bad, my recent experience in this thread would suggest that you know what you are talking about, so Ill just replace both.

[nickb]

I think they are J113 but better check.


https://www2.mouser.com/ProductDetai...Pvl0z7hwtK7ec=

I recall Mouser does have a cheaper USPS shipping option. The 'bay can be OK for small quantities but I'm always a little wary of the quality.

[slow6i]

I think they are J113 but better check.


https://www2.mouser.com/ProductDetai...Pvl0z7hwtK7ec=

I recall Mouser does have a cheaper USPS shipping option. The 'bay can be OK for small quantities but I'm always a little wary of the quality.

I just ordered from Digikey. They were J111's, and I needed some stuff for a head tracking rig that im building anyway so it worked out well!

Ill report back when they are replaced. Thanks!

[slow6i]

Alright, so Q6 and Q7 have been replaced, and the symptoms are still the same. Next steps?

[glebert]

OK, if jumping across Q7 works and replacing Q7 doesn't help then it seems like it must be what is happening at Q7's gate. Could it just be a broken input jack not releasing the inhibit?

edit: guess that was answered back around #22

[glebert]

Yes, the test was done after plugging a cable into the input jack. For confirmation, I unplugged it as I was measuring your suggestions:

Q7 Pin 1 is the "top" of the D shape looking down at it.

Pin 1	Pin 2	CR20 No Stripe	CR20 Stripe	CR21 No Stripe	CR20 Stripe
2 mV	17 mV	220 mV	5.69V	27 mV	7.95 V
0 V	-15.24 V	-15.84 V	-16.22 V	15.83 V	7.95 V	Cable Unplugged

Thanks!

The CR20 and CR21 no stripe are the same spot, right? How is one positive and one negative? Is that just a typo? Is the last column CR21 stripe? Seems like that should be more like 15V for clean channel (same as output of U8B).

[nickb]

OK, if jumping across Q7 works and replacing Q7 doesn't help then it seems like it must be what is happening at Q7's gate. Could it just be a broken input jack not releasing the inhibit?

edit: guess that was answered back around #22

Exactly what I was going to say

So go and redo the test but this time put the probe on the gate directly and also check the DCV on the source (of Q7).

[slow6i]

Exactly what I was going to say

So go and redo the test but this time put the probe on the gate directly and also check the DCV on the source (of Q7).

Clean channel, volume / tones up

Input Plugged
CR20 Stripe: 5.67 dcV
CR20 No Stripe:0 dcV
CR21 Stripe: 7.9 dcV
CR21 No Stripe: 0 dcV

Input Un-Plugged
CR20 Stripe:-2.50 dcV
CR20 No Stripe:-2.20 dcV
CR21 Stripe:7.92 dcV
CR21 No Stripe:-2.01 dcV

Input Plugged
Q7
D(1): -.39 dcV
S(2): -.39 dcV
G(3): 0 dcV

Input Un-Plugged
Q7
D(1): -.59 dcV
S(2): -.59 dcV
G(3): -1.15 dcVa

(Pin numbers per http://www.onsemi.com/pub/Collateral/J111-D.PDF )

[nickb]

There is something screwy going on there.

1) When unplugged there are different voltages on CR20 anode ( non stripe) and Q7 gate. Check the connection between them with an ohm meter.

2) When unplugged the inhibit signal (cathode CR20) should be close to -16V. Not that that explains Q7 not passing a signal, in fact it means that Q7 would always pass a signal

3) When plugged the inhibit signal (cathode CR20) should be close to +16V. Not that that explains Q7 not passing a signal either since Vgs>0 => pass a signal.

I suggest you check you do some DCV measurements around the input jack area first on both sides of R2 and then the inhibit side of R3.

[glebert]

If you get a chance check the output of U8 pin 7 with clean and dirty channels.

[slow6i]

I suggest you check you do some DCV measurements around the input jack area first on both sides of R2 and then the inhibit side of R3.

Continuity at CR20 and CR21 anode to Gate on U7 is confirmed

Plugged
R2 Brn: 10.5->8.45V
R2 Gld: 13.5-8.45V

R3 Brn: 10.5-8.45 V
R3 Gld: 12.3->5.65

Unplugged
R2 Brn: -17.2V
R2 Gld: -2.9V

R3 Brn: -2.9 V
R3 Gld: -2.27 V

U8-7 Plugged
Clean: 15.94 V
Gain 1 (Y):-16.3 V
Gain 2 (R):-16.3 V

U8-7 Unplugged
Clean: 15.98 V
Gain 1:-16.3 V
Gain 2:-16.3 V

@glebert I am going to be in Portland tomorrow around noon for rehearsal, I would be more than happy to meet with you and have you take a look at this thing if you are available / willing. I can DM you my contact info, if you are available.

[glebert]

I'm totally booked up, and really am stumped on this one anyway, so I don't think me poking at it is going to help.

[nickb]

Your measurements are inconsistent since we have different voltage reported for the same node under the same conditions (more than once) . Without reliable data it's impossible to draw meaningful conclusions.

What make and model of meter are you using? Does it have a known good battery? Where are you clipping your negative lead?

[slow6i]

Your measurements are inconsistent since we have different voltage reported for the same node under the same conditions (more than once) . Without reliable data it's impossible to draw meaningful conclusions.

What make and model of meter are you using? Does it have a known good battery? Where are you clipping your negative lead?

Its a Cen-tech 95670. Its certainly not a top of the line meter or anything. The battery is good afaik, though I will change it and check the voltages again. Negative lead is to the chassis just above the power switch. I am not using clips though, I'm using probes if that matters.