Mesa Boogie Formula Pre - Relay

[SIMPLINHO]

Hello everyone.

I have a problem in a Mesa Boogie Formula Pre. The relay that switches the channels when I turn on the pre, makes a noise. It seems that toggles between on and off rapidly, until the power source reaches the 12 volts. I experimented with a 9 volt battery connected directly and it works well. After some time on, the problem almost disappears.
Help me please. Thank you.

SIMPLINHO

[SIMPLINHO]

Hello everyone, again.

Please help me, if you can. I have some difficulty in expressing myself in English, so I do not write much. But I can understand your answers, so you can give me support. I thank you very much for your generosity once again.

SIMPLINHO

[chipaudette]

Hi,

There's not much talk of Mesa Boogie products on this particular board. Furthermore, people who use (or repair or modify) Mesa pre-amps on this board are even more rare. That might be why no one is replying.

You might have better luck at "The Boogie Board". Here's a link to one of their sub-forums that focuses on Mesa rack pieces:

The Boogie Board • View forum - Rack Pieces

Chip

[SIMPLINHO]

Hi, chipaudette.

Thanks for the reply. I'll take a look at the forum that you show up to see if I find what I need.

Cheers
SIMPLINHO

[Jazz P Bass]

Mesa Boogie Formula Pre

Here is the schematic.
Are you using the footswitch?
Is the problem still there if you do not use the footswitch?
You might want to check that your +12 volt supply is not being loaded down.
Page 7 is the internal circuit.
Page 8 is the foot switch.

[SIMPLINHO]

Hi,

Thanks Jazz P Bass for the schematic.

Are you using the footswitch?

Yes.

Is the problem still there if you do not use the footswitch?

Less, but still there.
The relay corresponding to the rhythm takes some time to be on and makes noise like a buzzer. The lead positions work well. Where there should be 12v has only 10v.
This pre had been changed by the previous owner, which makes it more difficult to find a solution.
Will you get me some photos of the interior to compare with mine?
It would be a good help too.
Thank you.

Cheers
SIMPLINHO

[Jazz P Bass]

Mesa Boogie

The rythym channel relay is chattering at power up.
Correct?
After being on a while it will not act up.
Correct?
Does the rythym LED blink when the relay is chattering?

[SIMPLINHO]

Hi,

The rhythm channel relay is chattering at power up.
Correct.

Yes when I have selected rhythm and without the footswitch connected.
With the footswitch, no noise, but the leds are all on, and without sound.
And when I select rhythm, the relay begins chattering. After some time,
the sound of the guitar appears mixed with noise. Channels lead ok.
I measured the voltages on the relay (RY 1), and they do not pass quickly
from 0v to 10v. I do not know if this helps.
I have looked on the net and I did not find layouts. Who has?
Would be useful to check some links.

Does the rhythm LED blink when the relay is chattering?

I think not, but I will confirm this.

Simplinho

[Jazz P Bass]

Mesa Boogie Rhythm Channel

According to the schematic (Page 7) RH1 is supposed to be OFF when selecting Rhythm Channel.
RH2 should be on.
Can you please verify this?

[SIMPLINHO]

Hi,

Quote:
Does the rhythm LED blink when the relay is chattering?

I think not, but I will confirm this.

I've checked out, and he does not blink.

Can you please verify this?

Now I canīt, I'm on my job, at home I'll check.
One thing I'm finding strange is the fact that after an hour on, more or less, the problem almost disappears. Be due to warming? Be a problem with the relay? Will be damaged? How can I check.
Still looking for layouts or photos and I canīt find anything, please help me,
if you can. Thank you.

Simplinho

[Jazz P Bass]

Mesa Boogie

You have to isolate the problem.
If the problem occurs with the footswitch connected it may be the footswitch circuitry OR the amp circuit.
If, upon disconnecting the footswitch, the problem goes away. then it is the footswitch circuit.
If the problem remains, upon disconnecting the footswitch, the problem is in the amp circuit.
Hope this helps.

John G

[SIMPLINHO]

Hi,

Sorry to be annoying.

If the problem remains, upon disconnecting the footswitch, the problem is in the amp circuit.

It appears to be the preamp circuit, but may be the relay, the IC or the transistor.
That's why I asked you the best way to test the relay.
Maybe I should buy a new one. It will be better.

Simplinho

[Jazz P Bass]

Mesa Boogie pre

The rhythm channel indicator is the green LED. Correct?
If so, actuating the rhythm channel selector switch should illuminate the green LED & supply relay 2 with a ground path, thus closing the relay.
That is all there is to the circuit.
The relay chattering may mean that the switch is not connecting to ground completely when it is closed.
Check switch continuity to ground when it is closed.
If that is o/k, replace the relay.

[SIMPLINHO]

Hi,

Without the layout I canīt find the relay 2. I do not know where he is so I canīt verify.
Also, I think I saw wires soldered out of place. I'm out of luck.
I have sent an email to the Mesa Boogie to see if they send me a layout.
Hopefully I get lucky.

Thanks Jazz P Bass

SIMPLINHO

[Jazz P Bass]

Relay 2

Follow the Rhythm Channel selector switch circuit board trace.
It goes right to it.