Fender FM15DSP no output

[ca7922303]

Powers on, no output. Old project. Recall tracing voltage from input. Not able to find where it stops?

[Jon Snell]

Check 5volts supply.
Check inputs on U-6
Check pin 3 U-6, it is quite straight forward.
Hope that helps.

[vintagekiki]

Hope that helps.

Enough for one who understands and knows.

[Jon Snell]

Insert a signal to the input jack. Follow it around the circuit using another amplifier as a monitor. If you haven't got one, remove a jack plug from one end of a known good guitar lead, strip the wire ends. Use a lead with a crocodile clip on the ground/screen and connect your isolation capacitor to the centre wire. I would suggest you use a 10n, (or anything near it as it doesn't matter), capacitor as a probe connected to the inner conductor and the screen to ground.

I usually start from the output and work backwards.
Keep a logical constructive method and don't forget, the faut is always the last thing you find, hence power supply followed by signal is the way forward.
As ca7922303 is repairing stuff, I dare say this is already in use.

[ca7922303]

Getting -110mv @ P4 (2000mv scale), no readings @ U6 on any scale.

[vintagekiki]

And what question do you have?

[ca7922303]

Was giving measurements to Jon Snell's 1st response.

[vintagekiki]

Dear friend

In 2 weeks you have opened 8 threads where you are fixing something.
Judging by your comments, from experience you have nothing but good will. I am not qualified to comment on your expert background.
I would just like to remind you in the friendliest way that every (your) intervention on the equipment implies (your) responsibility, if something bad happens to the user who entrusted the equipment (to you) for service.

Think about it.

[ca7922303]

I appreciate all the great help I'm getting and am learning from it and hope to learn enough to not have to ask so many questions in the near future.

[Jon Snell]

Getting -110mv @ P4 (2000mv scale), no readings @ U6 on any scale.

P4?
Check for sugnal on P11 Rin and Lin if you have signal check Rout and Lout, no signal means DSP board requires specialised repair. Nothing most people can do and I think they are obsolete from the supplier. Fleabay may have anothe FM15DSP complete at a reasonable price, if it is worth fixing.
Otherwise, remove the DSP module, connect Rin to Rout asnd Lin to Lout. You will have a very basic practice amp.

[vintagekiki]

Nothing personal. I want to help you.

It's not about questions. In order to ask questions, (certain) knowledge is required. Knowledge is not acquired in the near future (quickly, overnight), it is not acquired through portals, knowledge is learned in appropriate schools and from appropriate books. Portals are used for mutual exchange of experiences, where it is assumed that the participants have (some) knowledge.

Everyone who deals with something must know what not know, in order to know what are to accept, because ignorance (or not knowledge) does not justify consequences that may arise from it.

If you really want to learn, visit
https://music-electronics-forum.com/forum/schematic-requests/25212-links-to-books

[ca7922303]

Ok, got an auto ranging dmm now and previous measurements corrected if it makes any difference: P4(71.5mv), U6 pin#3(81.2mv), P11 RIN/LIN(90.1 mv), and my schematic shows a L OUT +(2.7mv) and L OUT -(0.00mv). Don't see a R OUT?

[Jon Snell]

Ok, got an auto ranging dmm now and previous measurements corrected if it makes any difference: P4(71.5mv), U6 pin#3(81.2mv), P11 RIN/LIN(90.1 mv), and my schematic shows a L OUT +(2.7mv) and L OUT -(0.00mv). Don't see a R OUT?

Unfortunately you must check for audio signal. Use another amplifier to listen for a signal. See post 4.

[ca7922303]

Can't find an R out on schematic on P11?

[Enzo]

I don't see where we covered the basics. is there ANY sound AT ALL? I mean any background hum or hiss from the speaker? SImple checks are the speaker - does it even function?

Do the headphones work? The phones jack has a cutout for the speaker and power amp. Dirty contact there quiets the amp.

Pin 1 of the power amp is its input. CAREFULLY touch it with a small screwdriver or even a meter probe. Does that make hum?

Q1 and Q3 are mutes, are they stuck on?

This isn't a stereo amp, they used Left, there is no use for Right. It isn't there.