Mesa Boogie F-30 Issues. Need urgent HELP. Please...

[louiev]

Hi Everyone,

I'm glad I saw this forum! This is my first post and I hope that someone can spare a little time and help me with these few issues my F-30 has been giving me recently. Just so you know beforehand I replaced 3 pre-amp tubes here(V1 - Driver tube, V2 - Gain Stage Tube and the V4 - Phase Splitter/Output to EL34s) and also 2 power-amp tubes(EL84s) I replaced it with TAD tubes. And also, even BEFORE replacing the tubes, it's been acting up on me, reason why I changed the tubes thinking that it's a tube issue. But I still get these following issues:

1.) On my clean channel, I get a gritty dirty clean sound even when the gain is set to low(11 o'clock) and I have my master volume up to a low volume(9 o'clock) I still get this annoying gritty clean sound. I DO get the clean sustain out of the tone, it's just that the actual tone I get gives me this overdriven-type sound which I don't get before.

2.) On the 2nd channel which usually I use for Overdriven/Distorted tunes, I get this Overly-Distorted dirty sound. Even when I set my gain to 1 o'clock, I don't get that usual overdriven classic crunch I used to get before.

3.) This ones pretty WEIRD.. Whenever I switch channels from CH2 to CH1, I couldnt switch back to CH2, what happens when I switch back to CH2, I don't get any sound at all, what I do is that I put the amp onto standby, the switch from CH1 to CH2 then turn it on again, that's where I get the CH2. This one is weird. I don't know how this happens. Even when I switch via Footswitch or the Knob switches I get the same problem. Bottom line, I couldnt switch from CH1 to CH2 without turning the amp onto standby and turning it on again.


I would appreciate any help you could give me. Any tips or DIY stuff I could try(I currently live in the Philippines and don't have access to any Mesa service centers since they don't have one here) please feel free to tell me.

I spent almost a couple of hours diagnosing the problem and I still couldnt find a solution for it. I tried to switch the old tubes back and forth, switched the new ones in, tried a combination and still no luck.

I also tried to see if the speakers are giving me the problem and this is what I did:
There's one problem I isolated though, I'm not sure if this has something to do with the speaker cab but I tried to plug a different amp(15watt Marshall Mini) and I get a good sound. I'm using a Kenwood 8ohm 80watt speaker for my amp and I'm not sure if this has something to do with it since I was getting a good sound when I have my other amp plugged in to the speaker.

I would really appreciate any help and time that you could spend in helping or posting to help me out.
Thank you so much and Greetings from the Philippines!

-Louie V

[Jazz P Bass]

Mesa Boogie F30 Schematic

You will need to verify that the switching matrix is working.(switching & muting circuit)Page 9 on the schematic.
After that, are the relay contacts good?

[guitician]

Is that the way the Mesa Co. presents the schematics to their service people?
It would seem like a relay, or the physical switches controlling them are failing. Or the +/- power supply voltages are off.

[louiev]

You will need to verify that the switching matrix is working.(switching & muting circuit)Page 9 on the schematic.
After that, are the relay contacts good?

THank you so much for the reply, sir. It's just that I'm not familiar with reading the schematics you have attached and have no electronics training whatsoever. Although I would like to try this out since I have no access to any amp tech in my area(Manila, Philippines). How would I know which one's which and how do I get started? Is this something I could do or I need a professional who could do it?

[olddawg]

Did you say you are using a Kenwood speaker? A Kenwood stereo speaker? Generally the foam surround on the woofer makes a modern hifi speaker awful for guitar. If you are using the crossover with the tweeter and the midrange it will be even worse. The channel switching issue is definitely a problem. With no electronics background at all it could be extremely difficult and even dangerous for you to service.

[louiev]

Did you say you are using a Kenwood speaker? A Kenwood stereo speaker? Generally the foam surround on the woofer makes a modern hifi speaker awful for guitar. If you are using the crossover with the tweeter and the midrange it will be even worse. The channel switching issue is definitely a problem. With no electronics background at all it could be extremely difficult and even dangerous for you to service.

Yup a Kenwood Stereo component speaker as of now. I had no choice since I sold my recto cab when I moved back here to the Philippines and had to use this one just for now. Oh I see, so this is somehow the root of the channel switching issue then? That is true I have no electronics background actually... I ordered a 2x12 cab the other day and I guess it's just a matter of waiting and trying it out on it. Hmmm... I just wanted to know for future reference how does using a component speaker affect the channel switching? Thank you for your reply, sir.

[Jazz P Bass]

Quote:"I just wanted to know for future reference how does using a component speaker affect the channel switching?"
You may have misinterpreted the statement.
The speaker has nothing to do with the switching circuit.
These Mesa amps are a pain in the a** to work on on let alone troubleshoot.
I would take it to a tech.

[guitician]

These Mesa amps are a pain in the a** to work on on let alone troubleshoot.
I would take it to a tech.

It's no wonder with schematics like that....

Yeah, since you are not a technically able person, you should forget repairing it yourself. Because telling you how to repair it would be almost impossible through a forum.