Aion fx comet - audio issue

[Teddeeh]

Hi guys so i finished building an aionfx comet.
No audio
just as a maybe problem fault finder, i get no signal from pin 1 of the IC. 5,6,7,3,2 all have signal using an audio probe but pin 1 is silent. This is with multiple chips. Pin 4 grounded.
1- 9.18
2-4.30
3- 4.86
4- ground
5-4.37
6-4.86
7-4.86
8- 9.8 v
I have used multi chips 5532, 4580, 358 etc.

[antonis]

Your issue have two options.. 

Either pin 1 is somehow shorted to +9V or op-amp is hitting the positive supply rail..
The later could be caused by a shorted C7 (1μF Box cap) due to high DC gain..

[iainpunk]

or the distortion pot, it looks like theres solder to far up the legs, which may cause the trace to disconnect from the connections. stick the meter on the two outer connections and check if the resistance isn't to high (expect 80k to 120k)

cheers

[anotherjim]

I had a quick look at the build pdf and came away baffled. It suggests you can use the original single opamp or a dual, but the schematic shows the dual wiring as a snippet (same as current DS-1 with one opamp a buffer). What I couldn't see was how that works with the PCB.
Are there links you have to fit according to the chip type or is the dual DIP on a daughter board?

[Teddeeh]

I had a quick look at the build pdf and came away baffled. It suggests you can use the original single opamp or a dual, but the schematic shows the dual wiring as a snippet (same as current DS-1 with one opamp a buffer). What I couldn't see was how that works with the PCB.
Are there links you have to fit according to the chip type or is the dual DIP on a daughter board?

No, i do believe it is laid out for a dual op amp- hence the design notes calling for a 3404 or jrc4580 equivilant.

[Teddeeh]

Your issue have two options.. 

Either pin 1 is somehow shorted to +9V or op-amp is hitting the positive supply rail..
The later could be caused by a shorted C7 (1μF Box cap) due to high DC gain..

Reccomend replacing the 1uf cap then?

The distortion pot measured aaround 95k

[antonis]

Reccomend replacing the 1uf cap then?

Not necessarily..

Fistly, lift any leg of 1μF cap up to see what happens..
(op-amp should behave like a non-inverting buffer with no gain..)

[Teddeeh]

Reccomend replacing the 1uf cap then?

Not necessarily..

Fistly, lift any leg of 1μF cap up to see what happens..
(op-amp should behave like a non-inverting buffer with no gain..)

Nothing changed.

[antonis]

Nothing changed.

If so, check for some kind of short between +9V and pin1..
(power off and measure resistance..)

[Teddeeh]

Nothing changed.

If so, check for some kind of short between +9V and pin1..
(power off and measure resistance..)

measuring 485k

[aion]

I had a quick look at the build pdf and came away baffled. It suggests you can use the original single opamp or a dual, but the schematic shows the dual wiring as a snippet (same as current DS-1 with one opamp a buffer). What I couldn't see was how that works with the PCB.
Are there links you have to fit according to the chip type or is the dual DIP on a daughter board?

That would have been the legacy PCB... the current one (which is what he's using) only supports a dual opamp. Here's the build doc -
https://aionfx.com/app/files/docs/comet_documentation.pdf

The high pin1 voltage is definitely a major red flag, although based on the resistance test I do wonder if it's a measurement error. All the other IC pins look OK and I can't see how pin 2 would be normal but pin 1 would be off when they're just connected through a resistor (the distortion pot).

You might try soldering the transistors into the sockets to make sure that's not the issue. Those type of sockets loosen after 1-2 uses and they don't hold transistors very well. I stopped socketing transistors a few years ago and only do ICs these days. If any of the transistor legs are not making good contact then it would cut out the sound.

[anotherjim]

Pin1 voltage seems too high to be the opamps positive swing limit, but you never know, it depends on the load to some extent.
However, pin2 voltage is lower than pin3 and that does suggest to me that something is pulling the far end of R10 negative toward 0v and the feedback from pin1 cannot go any more positive to pull pin2 up to equal pin3 voltage.