Fender Frontman 212R loosing power

[Emetal]

I am looking at a Fender Frontman 212R that friend claims it's loosing power when playing loud at practice pad, however it is playing perfectly on bedroom levels. Visually I do not see anything that stands out. Did anybody have similar experience with this amp, what should I check?

[DrGonz78]

Sounds like a loose intermittent connection in the amp that is only being triggered by the loudest of vibrations. Try injecting a signal into the amp while giving the cabinet a nice whack or two with your fist. Does this trigger anything? Take the chassis out of the amp, inject a signal and use a chopstick to move around specific connection points. Does this trigger anything? Look at the schematic and locate the areas on the board that comprise the power supply sections. I would chopstick those areas the most to really get at it. Does the light on the front of the amp go out when "it's loosing power" or does the sound just cut out?

[Leo_Gnardo]

what should I check?

Any amp, mixer, or other item that has FX loop or pre out/power amp in jacks:

https://music-electronics-forum.com/...ad.php?t=28549

[Mick Bailey]

After verifying the FX loop is OK I would take a look at the solder side of the board and inspect the joints specifically where there are any power resistors (R144, R145 etc) and around the output transistors. Look out for any grey, rough-looking joints where there may be a circular crack around the solder of a component leg.

[Enzo]

And when the complaint is sound cutting out at high volume, you won't find it playing quietly.

[Leo_Gnardo]

And when the complaint is sound cutting out at high volume, you won't find it playing quietly.

That's when I break out Maxwell's Rubber Hammer. I figure it's large vibrations causing the havoc, and that way my neighbors don't have to listen to a heavy metal serenade.

Of course you can whack it with your fist. For me, the thrill wears out quickly. Sing along with that 50 year old Beatles song, works for me!

[Emetal]

Well one more time I learned not to take clients word for granted but hear the problem for myself. Since I could not find anything in home/bedroom I took it to the practice pad and as soon as I cranked it I found out there is nothing wrong with the amp but one of the SPEAKERS is blown, it's rattling and it is measuring only 2,5 Ohms instead about 8 as it should. Problem solved, thanks to everybody for the ideas and sorry for misleading info. If they told me "rattling" instead of "losing power" I would have pay attention to the speakers right away.

[Helmholtz]

and it is measuring only 2,5 Ohms instead about 8 as it should.

Not really relevant here but the DCR of an 8 Ohm speaker is ca. 6.3 Ohm.

[Enzo]

Yep, 2.5 ohms sounds like a 4 ohm speaker.

[Emetal]

I believe that both of these should be 8 Ohms speakers because the one of them that is showing DCR 8,4 Ohms sounds great, the bad one is showing DCR 2,4 Ohms and it's rattling, farting..