Hi all,
Semi-noob here, please excuse my ignorance. I recently came into a Fender Frontman 212R that has issues.
I power the amp on and the speakers immediately emit a wild, loud crackling sound. I've done some sleuthing... so far here's what I've found...
The pre output is clean, if I plug my guitar in and listen it sounds perfect. I tested the resistance of the speakers themselves and they are reading well. Checking voltage on the outputs confirms wild voltage fluctuations.
I have wiggled all board components and found nothing loose, also no burn marks on any components. Caps are not bulging and appear normal. I have checked continuity on the output transistors, nothing there.
Any thoughts on what this could be? Seems like it must be something in the output stage...
Thanks in advance for your guidance and input!
Attaching a picture of the board for reference:
Semi-noob here, please excuse my ignorance. I recently came into a Fender Frontman 212R that has issues.
I power the amp on and the speakers immediately emit a wild, loud crackling sound. I've done some sleuthing... so far here's what I've found...
The pre output is clean, if I plug my guitar in and listen it sounds perfect. I tested the resistance of the speakers themselves and they are reading well. Checking voltage on the outputs confirms wild voltage fluctuations.
I have wiggled all board components and found nothing loose, also no burn marks on any components. Caps are not bulging and appear normal. I have checked continuity on the output transistors, nothing there.
Any thoughts on what this could be? Seems like it must be something in the output stage...
Thanks in advance for your guidance and input!
Attaching a picture of the board for reference:
So many parts, try hitting them one at a time with freeze spray after it's warmed up, with a junk speaker.
Chemtronics - ES1052 Freeze Spray — GoKimco
Chemtronics - ES1052 Freeze Spray — GoKimco
Quite probably frayed tinsel wires in the speakers.
Put amp on a table, with the back/speakers towards you.
Turn room lights OFF or leave just some desk lamp pointing at a faraway wall/door/curtain so ambient light is dim, and turn amp on.
You should see tiny blue sparks coming from inside speaker backs.
If so, they can be replaced.
Put amp on a table, with the back/speakers towards you.
Turn room lights OFF or leave just some desk lamp pointing at a faraway wall/door/curtain so ambient light is dim, and turn amp on.
You should see tiny blue sparks coming from inside speaker backs.
If so, they can be replaced.
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If I am reading fluctuating voltage off the amp, would this not rule out failure in the speakers?
Not necessarily, full power "explosions" connecting/disconnecting speakers will be reflected in power supply voltages.
But instead of typing here, why don´t you actually test it?
It takes all of 5 minutes.
Now you have extra homework (besides the above test
) :
Scope speaker out, scope supply rails, and post results.
But instead of typing here, why don´t you actually test it?
It takes all of 5 minutes.
Now you have extra homework (besides the above test
) :Scope speaker out, scope supply rails, and post results.
all these models suffer from intermittent solder joints and the best way to resolve that is to fully remove the PCB and visually inspect with a magnifying glass and reflow all suspicious looking joints.
also don't neglect cleaning the pre out, amp in jacks! they are also a common source of troubles.
also don't neglect cleaning the pre out, amp in jacks! they are also a common source of troubles.
Thank you all for the thoughtful replies!
I checked out the tinsel wires while the amp was powered on. No sign of electrical arcing there.
Took out the PCB and inspected the connections. I discovered two noteworthy areas -
Scorching around some of large white rectangular resistors:
Also, a little bit of scorching/deformation around this lead, the white lead coming in off the power switch
Seems to me that the resistors are a common cause of issue and the likely culprit. Would you all agree?
I checked out the tinsel wires while the amp was powered on. No sign of electrical arcing there.
Took out the PCB and inspected the connections. I discovered two noteworthy areas -
Scorching around some of large white rectangular resistors:
Also, a little bit of scorching/deformation around this lead, the white lead coming in off the power switch
Seems to me that the resistors are a common cause of issue and the likely culprit. Would you all agree?
which resistors are those ? (they should be marked on the component side) with the extra flux around them i'd say they where already retouched.
if you've got a magnifying glass i'd use it to check things out closer.
all the pots and jacks are another common point of stress failure so check those.
if there's a way to provide additional mechanical support to those power resistor i would do so.
if you've got a magnifying glass i'd use it to check things out closer.
all the pots and jacks are another common point of stress failure so check those.
if there's a way to provide additional mechanical support to those power resistor i would do so.
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seeing as those are the dropping resistors to the low voltage supply any grief there could wreak havoc as either rail could be cutting out...= NASTY!!!
it's not outside the realm of possibility that the zeners and C76,76 could be breaking down as well.
hold the phone without verifying serial number to product revision the schematic i'm looking at lists them as 200 ohm 5 watt...?
it's not outside the realm of possibility that the zeners and C76,76 could be breaking down as well.
hold the phone without verifying serial number to product revision the schematic i'm looking at lists them as 200 ohm 5 watt...?
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