Did you put a knob on the shaft before you tried it ?
Some of the older ones might need a bit more force to turn the last bit so it activates the switch.

That part number is given as a substitute part for a Peavey Studio Pro 40 in this article:
https://www.ssguitar.com/index.php?topic=1593.0
I have no idea if it is accurate or not

I am not sure if this is the same or if you can get it but its available in Italy.
https://www.folliemusicali.com/prodotto/fender-outlet-0057799000-pcb-udsp-micro-dsp-for-deluxe-90/

USA:
https://reverb.com/item/67584695-fender-dsp-board-with-processors-2002

If you think the fault is in U4 then see if you can get a new chip and have someone copy the program from the 100 amp into the new chip, it is only an Eprom.

Here is the link to the other site pa911 mentioned :https://music-electronics-forum.com/forum/amplification/guitar-amps/maintenance-troubleshooting-repair/986153-fender-acoustasonic-30-dsp-with-very-audible-hiss

I can't help but someone might be able to.

And the schematic: You cannot view this attachment.

If nothing else comes out of it, the experience you are getting out of this is priceless in the long run.
Keep it up.

Edit: And most likely cheaper then spending your time in the local bar as well.

I tried to clean up the pictures, I don't know if it is better or worse.
Also some data sheets.

I think it would be a very big step to try to understand "Logic IC's" from the start.
There are several websites to learn from, and also many books and information on the NET that can guide you on the subject. Texas Instruments have some good info but it might get complicated very fast.
I would start here : https://learn.sparkfun.com/tutorials/digital-logic/all

The first picture shows you have a +4.8v supply that goes to 4 IC's (IC-301 to IC-304)
Pin 14 on the IC's is the positive voltage supply pin (Marked VCC)
Pin 7 on the IC's is the negative voltage supply pin (Marked GND)

In schematics VCC is often the marking for the positive supply, GND is the ground or 0V supply and finally VDD is often the negative supply.

So basically it just shows you have +4.8 volts to pin 14 on those chips and 0 volts on pin 7.

The second drawing you did is of IC303 (SN7472), it is a block diagram of its function, that IC is a "AND GATED J-K MASTER-SLAVE FLIP-FLOPS WITH CLEAR AND RESET".
What that means is that that is the very deep end of the pool for you where headaches lurk, you can try to understand it by reading up on it, I do and it gives me a headache even thinking about it.

All of those logic IC's have modules in them, and the modules are drawn with different symbols that indicates what they do, if you deal with them often its easy to follow but its been to long ago for me to try.

You might not be able to get the exact replacement part for all those IC's but there are many other chips that can do the same function with slightly different part numbers.

I found this page with lots of info on other model oscilloscopes, but not your one.
It is possible they might have very similar schematics or even the same.
Have a look :
https://www.vintage-radio.info/heathkit/index.htm

and just as I was going to press "post" I found these photos:

You cannot view this attachment.You cannot view this attachment.You cannot view this attachment.You cannot view this attachment.

It's best to open the pictures in a new window, or download the link when on the small pictures.

Heathkit Cross Reference:
You cannot view this attachment.

Whats the model of the Scope ?

Quote from: saturated on October 01, 2023, 02:52:19 PMon my to do list...need to build a curve tracer and connect to my oscilloscope

I don't know if you have a transistor tester yet, but a modern one can be a great item to have, for very little money you can pick up something that can do some amazing measurements on components.
I bought one several years ago but I think I need a new better one as they get better so fast.
I bought one without a case but then ended up buying a case many years later so the final cost was the same as one with a case in the first place.
The old one I have now is in this video on you-tube, the one on the right.
It would be worth spending some time and finding a very cheap one that can do everything the more expensive ones can do, just have to keep looking till you find one.

https://www.youtube.com/watch?v=-pEmM0Kt2UY

Cheers
Mick
 PS...If you find a great cheap one ....let us know

I could not see the schematic, so I will post the ones I have if someone is interested.
Photos would be very nice.You cannot view this attachment.You cannot view this attachment.You cannot view this attachment.   

while I got you here I am really struggling with trying to understand how to be safe with oscilloscope grounding.
I was going to put a two prong adapter on the cord to unground it but maybe that is not a good idea.
[/quote]

It has been a long time since I used my scope, and my scope is a real CRO.
I usually use one ground clamp that I attach to the 0v rail, as long as the 0v rail is grounded.

All my probes have a removable ground wire so all I am left with is the probe itself, I leave one probe with the ground wire attached.
My old "cathode ray oscilloscope" is nothing like the modern units most people have today, turn it on, have a cupper, use it.

What model are we talking about ?
I have only one Mark Bass service manual, the Little Mark 2.

I have had a good look for this schematic but i can't find one either, are you going to repair this one yourself?
I think this might be a very simple circuit as they sold very cheaply when they came out, it might not be hard to trace out.

If you can open the amp up and take photos of both sides of the PCB we might be able to trace it out for you, the more pictures the better.

I would imagine this might be a good project for people to build and also it sounds ok for a small amp, it might even be ok as a small stomp box size practice amp that you can plug into a speaker cab.

Cheers
Mick

These might have them,

https://www.esr.co.uk/components/transistors.htm

I think the BC337 would be ok as well