Help please!!

[scunnerlad]

I own a Fender Frontman 212r. when playing onstage Saturday as i played a loud note the amp suffered what can only be described a momentary loss of power with a large bass boom, this happened on either channel with different guitars / leads, weather plugged through stomp boxes or direct, or with footwitch plugged in or out, switching between the clean and the drive channel i noticed the LED for the channel went off and then come back on as soon as the note was finnished or cut, it happened less when the guitar was turned down or played softly but didn't go completely , this amp has been my main amp and i have never had a problem - until replaced recently with a Blackstar (which coincidentally has gone back to the shop with a valve problem!! ) and i now have nothing! My Farther is a qualified electical type bloke who could prob repair if i can point him in the right direction. Any suggestions (apart from not buying a blackstar!)

Cheers Guys

[soundguruman]

Resolder all the connections on the circuit board, clean or replace all the jacks and controls.
This sort of think happens pretty often on old amplifiers. Just needs routine type service.
Hope you know a good technician. Don't try it yourself without the tools and experience.

[mozwell]

This may help
If you are not sure about electricity, dont open the unit up & take it to a good service tech. Mains electricity can kill you.

If the channel led's flash when you play a loud note, i woudl check the pwoer supplies to see if they are stable...
Also check testpoints TP20 through to TP27, to see if they match the schematic. Also look to see if they are stable when you play a loud note.

Check (reflow) all solder joints, clean jack contacts, etc.

If you plug a guitar lead from the preamp out to poweramp in jack, do you still have the problem

[J M Fahey]

Apply the Enzo wack.
A good thump with your closed fist on the top of the amplifier (obviously, on and set up for playing).
Does anything happen?

[Steve Conner]

Yep and along the same lines, check the big filter capacitors (biggest components on the internal circuit board, look like large cans) for bad solder joints.

[scunnerlad]

hi gents and thanks for the info, stripped and checked, this was very clean inside no scaring/ marks on board have found one loose part labeled R144 on the schematic, the stem was just sat in the hole, block style resistor labeled 5WR330RJ My dad thinks prob not enough stem to re-solder, phoned Fender Service and they don't stock small parts as Amp class is too low for repairs (only stock inputs and pots), Any ideas where i can locate such a part (I am UK based) or if it can be replaced with a similar/ diff part? Hopefully this is the cause of the issue - dad thinks as hitting loud notes the reverberation of the amp was wobbling the connection causing the break in the circuit

[Steve Conner]

"Not enough stem", that's a new one on me! He should be able to resolder it anyway. Your dad is absolutely right as to the diagnosis, this loose connection explains your problem.

If you need a new one, it is a 5 watt, 330 ohm cement block resistor. Something like Maplin order code W330R or L330R.

[J M Fahey]

Dear Steve:

"Not enough stem", that's a new one on me! He should be able to resolder it anyway.

probably means that, ¿by vibration?, one leg cracked/split "just above" the PCB surface, component side.
That would leave you with a visible stem, 1mm too short to go through that hole, let alone able to be soldered to the pad , solder side.
Yes, it can be repaired with a short piece of wire, but the other leg must be quite weakened too by now.
jm2c

[scunnerlad]

thanks gents - think hes going to try and bridge connection with different wire to try and fix most of the major distributors don't carry the part with the correct variance ( im quoting my old man here ) Schematic reads 10% Maplins ect seem to be 3-5% which are too low the extra 5% could be a crucial factor but may not be but not worth trying as my blow/ not work or cause other problems

[Steve Conner]

A 5% tolerance resistor is better than a 10% one and can replace it with no problems.

JM could be right, maybe the other leg of the resistor is ready to snap too.

[scunnerlad]

Thanks Steve, dad wasn't too sure as what function the resistor served being a musical instrument amp whether the 10% was allowed/ required for or to do with increased volume situations through the guitar input (effects ect) as never really repaired things on the "musical" side (ex industrial and HV Electrican by trade with a bit of house "bashing" ) he was working on the basis of "must be listed on the schematic for a reason or why list it" i will let him know, He is planning on removing the entire piece and to inspect before re-seating / soldering - poss replace now with your info

[scunnerlad]

and for other info have a new Blackstar to replace the broken one gigged on saturday and seemed not to have any issues so the when the fender is fixed it will be back to being a backup,

[Enzo]

You and dad should keep in mind that this is just a guitar amp, not a space probe. Close is usually good enough when exact isn;t available.


Imagine your voltmeter had a 10% accuracy - any reading would be within 10% of the actual voltage. Now imagine a new voltmeter with a 3% accuracy. Its readings would be within 3% of the actual voltage. You could always use that more accurate meter when the crude meter was good enough at 10%.

Likewise those resistors. A 10% resistor means it won;t be more than 10% off from its named value. A 3% resistor will be within 3% or less. If the circuit allows a 10% variation, you surely can use a part that is closer to the value specified.