Help this newbie with a Fender Frontman 15R

fossil said:

I've got the chip all set but every time I power up the amp. I get a hum through the speakers but no guitar sound. I checked for continuity as well but nothing by hum...

Click to expand...

You need to check for high dc at the speaker out put end the amp will power up with no speaker connected... Question did you just fit the ic and power on?. Use a 10 ohm 10 watt resistor instead of the speaker.

Check the supply voltages, preamp voltage would be 15 plus and minus and the rear amp supply would be say 18 to 22 plus and minus v.
The speaker output voltage will be in mv volts..
Try not to just change parts at will as your waste time and parts.. Check the small opamp ics in the preamp circuit.

Marshall..park.. Fender small type amps are more or less the same..

Tann-44 said:

You need to check for high dc at the speaker out put end the amp will power up with no speaker connected... Question did you just fit the ic and power on?. Use a 10 ohm 10 watt resistor instead of the speaker.

Check the supply voltages, preamp voltage would be 15 plus and minus and the rear amp supply would be say 18 to 22 plus and minus v.
The speaker output voltage will be in mv volts..
Try not to just change parts at will as your waste time and parts.. Check the small opamp ics in the preamp circuit.

Marshall..park.. Fender small type amps are more or less the same..

Click to expand...

Yes, I did fit the IC and power on with the speakers... oops. I'll check what you said though.
Stupid question but how do I check the supply, preamp voltages : )
I'm not changing anything else, just did the TDA2050 and it's not blowing anymore fuses so that was part of the problem.. continuity is good too..

If the preamp chips are 8 pin devices (probably 4558) then power is on pins 4 and 8, and will be around 12 to 30v.
When you switch on the speaker should remain still, or just move a little and return to normal, if it moves right in or out then there is dc accross it, and this is bad, if the 2050 is ok and being new ought to be maybe the supply to it is bad, or down on one of the rails, did you measure the supply to the 2050 (pins 3 and 5), also there should be a largeish resistor and capacitor to ground accross the speaker o/p, this is the zobel network, does the resistor look as though its been cooking?

I checked the speaker wires first and there a slight DC current coming through.
Next, I went through the 2050 (pins 3 and 5) and got nothing!
With the speaker wires off, there is a slight buzz when I turn the amp on now ... sounds like nothing major, but its not completely silent so I'm mentioning that incase that's not normal. Here's what doesn't seem normal ...the amount of HEAT that tda is producing in the short time I take to check the circuit... the heatsink is burning!

I stuck the negative lead in the chassis for ground and checked the pins with the positive lead as you guys suggested. Didn't see any capacitor next to the speaker but there are two largish ones sitting on the circuit board.. nothing on the board seems like its cooked.
There are two BA4560s chips - and i cant get any reading off of them either..

That tda should not be burning that hot!! Remove it has it many of been damaged via a short circuit to ground.
You might need to order a new 1..the circuit will power up with out tda in, next your have to check each stage, power supply etc. when looking at the board you will two large caps these will be plus-minus say 18volts next the preamp volt will be say plus/minus 12v. Recheck posting as pin outs have been commented on.

Unit till this amp is working again don't connect any speaker load to it as it may get damaged!
Try and down load the circuit to aid fault finding.

Just found the schematic the supply feeds are 22volts and 15volts for the preamp..

Hey guys - happy new year to you.

Just wanted to let you know, I replaced the TDA again (because of the heat it was putting out) and all's well. The amp lives! It 'pops' every time I turn off the power-switch but that's not something new, it's always done that. Thanks a bunch for all your help! Cheers.

Good news the amp is working and a good learning to fault finding..

Happy new year...