weird power problem - Digitech GNX 4

[randers1]

DrGonz thx for the bump request. Jazz P Bass, will check the voltages tomorrow

[randers1]

From the top down, off of L36, 3.31V, off of L50, 3.35v, off of L51, 4.93v, I had trouble getting a reading off of U37, I think it flashed 12 or 14v one time. I was unable to duplicate.

[Jazz P Bass]

You obviously have a boot problem.
Seeing that the voltages seem o/k, my next step would be the timing crystal.
Again, this thing is a computer in a pedal box.
Not an east thing to try and repair.

[g1]

Were you checking those voltages when it was not starting up?
You will need to do checks when faulty boot, then compare to working boot. That will be tough as you will have to keep letting it cool down to get the fault condition.
Aside from the voltages Jazz mentioned, check the reset lines of U5 and U11 (pg.7).

[randers1]

I didn't check the values on a hung restart, I will do that next. I realize it must be tough to fix since the authorized shop couldn't, I really appreciate your guys time and interest. Unfortunately I am going out of town for the next week and a half, I will be back the Monday after Thanksgiving and recheck the voltages. I hope you all have a great holiday and I will post that Monday night.

[tlm2408]

Just signed up to offer some help. I had the same thing happen to me about 7 years ago. It turned out to be the power transformer, it wasn't putting out enough current anymore. Replaced it and it's been going strong ever since. I hope this helps

[krafty cat]

Good morning

I am French and I use a Google translator

I just registered on the forum regarding this specific problem on the GNX4.

My GNX4 no longer turns on. I'm a little confused and I really want to fix it. I have very limited or no knowledge of electronics but I have a multimeter and a soldering iron and I am very motivated and I asked ChatGPT for help to help me identify the fault. And actually I think there was a power surge in my apartment which is probably the cause of this outage. I have a power strip with a surge that started making a strange noise that I replaced. I checked that the gnx4's power supply works well by connecting it to another pedal which operates at 9V and this allowed me to see that the problem does not come from the power supply. I then had a sort of mystical revelation where I had the sensation of seeing the number 101 everywhere in my apartment and while inspecting the printed circuit board of the GNX4 I saw a component with 101 written on it. As I didn't know what the component was, I gave chatGPT a description of the component and it could be that it was a 100volt varistor. I asked chatgpt to explain to me how to use a multimeter to determine if this component was working properly and it seems like it no longer works but I'm really not sure because I'm new to electronics. And then all this is not very rational of course but I have had a lot of mystical revelations in the past which turned out to be correct even if I remain skeptical despite everything...

It could be chance or some kind of intuition that led me to identify the problem but I find it hard to believe it myself and I prefer to ask for help from humans who know about it because I I don't know anything about it.
My thing is rather music and plants.

Could you tell me if the component with 101 written on it is indeed a 100 volt varistor?


And could you tell me where I could buy this component to try to replace it?

[krafty cat]

I hope someone can help me because I don't know if I can trust Chatgpt based on my description of the component and I'm not very confident of my skill with the multimeter which I might have use wrongly.

I don't think I can buy a Fender Mastertone pro to replace my GNX4 even if it's the only pedal board that interests me if I had to replace it...

I also thinked that I could remove all the plastic components of the circuit board and put the circuit board in the oven at 180°C during 20 minutes to make a reflow but I never tried this before...



https://music-electronics-forum.com/...etch?id=918291

[g1]

Could you tell me if the component with 101 written on it is indeed a 100 volt varistor?


And could you tell me where I could buy this component to try to replace it?

The component is not a varistor. It looks like a coil and should not be the problem.

It will be much better if you start a new thread. Go to this link and click on the button that says '+ New Topic' :
https://music-electronics-forum.com/...guitar-effects

[krafty cat]

Thank you for your answer!

It looks like a coil indeed!! and the fact that its value is close to 0 ohms seems normal according to chatgpt.


I'm pretty sure there was a power surge that may have damaged the GNX4.

Does the component which is flat and square and yellow next to the power outlet in the attached image could be a varistor?

If not, do you know what could be this component?

As my problem is similar to the initial thread I do not find it relevant to start a new thread. There are already elements in this one that can help in solving similar problems to fix the GNX4 but I might be wrong.

You can also explain to me why It will be much better to start a new thread.

During this time I'm going to ask chatgpt if it can help me to identify the yellow component next to the power outlet.

Thank you


EDIT :


Thanks to chatgpt I was able to identify the flat yellow component next to the power socket as indeed being a varistor.

It says 30U250 on it. I tested it using the multimeter and its value is zero.

It appears to be short circuited. So I think it needs to be changed.


I was also able to identify a few diodes which seem to be in good condition.

Maybe I'm lucky if only the varistor needs to be changed.

[g1]

The square yellow part is the fuse shown as FS2 in the schematic. It is a self-resetting fuse. It should read zero ohms, so it must be good.
The next step would be to check for proper voltages coming out of the voltage regulators,

[g1]

I checked that the gnx4's power supply works well by connecting it to another pedal which operates at 9V and this allowed me to see that the problem does not come from the power supply.

The gnx4 requires 9V AC supply, not DC. Are you sure it is the correct supply?

[krafty cat]

So in fact the yellow component is a film fuse or SMD (surface mount design) fuse and you are right, it works correctly.

I assume it's kind of weird to try to ask to chatgpt for this kind of stuff...

The power supply is the original one. It worked fine for many years since I bought the GNX4 many years ago (EDIT : In fact I've had it for 20 years)

I don't know if it's AC or DC. (EDIT : yes it's AC)

Here is what's written on it :

Harman Pro Group
Model: PSS3-230
MFG. P/N: ST48-090-2100A
INPUT: 230V ~ 50Hz 35W
OUTPUT: 9V ~ 2.1A
CSA FILE NO: 183200

I plugged it into a MOOER Acoustikar 9V pedal and the pedal lit up so I concluded that the power supply was working but I might be wrong.

And you are right the mooer is a DC so from what I understand it might not be relevant to conclude that the power supply is working

But when I plug this power supply into the GNX4 it no longer turns on

I also tried with another power supply which is an AC DC adaptor on wich I can select the voltage and polarity but the GNX4 didn't work with it

this other power supply AC DC adaptor is :

MODEL : MW108
INPUT : 230V ~50 Hz
POWER : 11W
OUTPUT : 3-4.5-6 7.5-9-12 V
CURRENT : 500mA6VA(max)

and this power supply works fine with other devices but not with GNX4

I probably don't have any other power supply which would fit with the GNX4

Is it possible that my original power supply doesn't work anymore with the GNX4 despite the fact that my original power can work with a 9V DC pedal?

I have another power supply from a Yamaha RM1X which is AC but it's a 12V so I didn't try...



Thank you for your help I assume that I may try with another power supply which would be AC 9V so I'm trying to find one in my apartment but I rather go to sleep because it's 5:48 AM where I live

I might end up buying the Fender Tone Master pro if I can't get the GNX4 fixed

[g1]

Is it possible that my original power supply doesn't work anymore with the GNX4 despite the fact that my original power can work with a 9V DC pedal?

Do you mean the Harmon PSS3-230 will properly run some other pedal? Which pedal?
Yes, the Harmon supply is AC. The ~ symbol means AC.

[krafty cat]

I plugged it into a MOOER Acoustikar 9V pedal and the pedal lit up so I concluded that the power supply was working but I might be wrong.

And you are right the MOOER Acoustikar 9V pedal is a 9V DC pedal and not a 9V AC

so from what I understand you said, it might not be relevant to conclude that the power supply is working correctly?