Rockford Punch 301m

[mbates14]

The board # is PC-4309-H

I need the following values to these listed parts, they are blown to bits beyond recognition:


R37
Q112
Q113
R173
R50
R33
R45
R153, R198, R154, R183, R104, R186
Q10
Q107
R156
R149
R146

This what i physically see blown/cooked and cannot make out.

who knows what else is bad. probably all the outputs too.

 

[Perry Babin]

Email me if you want the schematic diagram.

babin_perry@yahoo.com

 

[mbates14]

Got everything done, but now i am having a serious issue.

The 9540 output side is working normally. the IRF540 side is blowing the fets. there is +25V between G and S

Further troubleshooting reveils that the bases of Q12/Q13 is only -13v. While Q10/11 is +37v

Tracing even further back, Q116 isnt turning on, it appears to be a current source? not sure. But it isnt turning on. Therefore, i am not getting the -37v where there is only -13v

any ideas? i checked all remaining resistors and transistors, comming up empty.

 

[Perry Babin]

How much current is is drawing before the transistors fail?

Does it blow them if they're clamped to the heatsink?

Is there any DC on the positive speaker terminal? If so, is it positive or negative (black probe on the amp ground)?

What's the rail voltage?

 

[mbates14]

rail voltage is +/-40v

I did more troublehsooting, the BIAS transistor Q109 isnt turning on, so about 2 to 4 seconds after powerup, the entire bias circuit pulls negative. -13v forcing the IRF540s past thier gate specs.

The gates start off about 0v. then when the bias circuit snaps negative, the vGS shoots to +25v which blows the IRF540s.

DC doesnt become present until 540s short at poweron.

I have the outputs removed from circuit. the IRF9540 section of the amplifier is working perfect.

I cannot find Q110 anywhere, so theres a chance this schematic may not be correct.

 

[mbates14]

Also Q109 was one of the blown ones, in the BIAS network. i replaced it already.

 

[mbates14]

i tried replacing Q111, made no difference. its collector starts at 0v and snaps to -13v.

 

[mbates14]

I removed Q111 to stop the BIAS circuit from getting its negative source, it allows the IRF540s to run without getting blown. But no audio from that half of the amp, still no negative half of the wave on the output.

Sooooo, i noticed it has 2 sets of differential drivers. My guess is one of them is toast. the transistors are statically checking ok, same with the resistors, but i guess that dont mean it isnt breaking down under load.

 

[Perry Babin]

If you lift D104? (connected to Q116?), do you get the bottom half of the waveform?

The ?s are because the numbers are hard to read.

 

[mbates14]

I am at a loss. Here is the scope shots, I am using a 1.25Khz Sine Wave as an input signal.

These are AC measurements. DC is too far off the scale over signal. So i cant really measure.

The input signal is shown, the rest are taken off of the collectors of Q102, Q103, Q104, Q105 which is the differential setup.

I replaced ALL transistors. problem still exists.

 

[mbates14]

I removed D104 Same deal.

Here are the scope shots from the Base of Q112, and Q113 (AC Mode)

 

[mbates14]

Here are DC measurements of Q111 Collector, Q109 Collector, and Q111 Collector with no RCA cables plugged in.

5V/Div

 

[mbates14]

Q104 Emitter reads 13.2VDC, collector and base read 12.5VDC.

While Q105 Collector is -12.1VDC, Emitter 13.1VDC, and Base is 12.5VDC

 

[mbates14]

I fixed it. R179 was open. read fine on board, dead out of circuit.

 

[Perry Babin]

That makes it tough to find.

 

[mbates14]

i broke it again. lol.

It was working fine, then i noticed R177 and R178, both 20ohms were reading about 500 ohms again. So i decided to replace them, and boom. blew out a new set of fets again. HMMMMMMMMMMMMMMMMMMMMMMMMMMM

 

[mbates14]

Im sorry, I didnt blow the FETs, i blew the Q12/Q13 drivers short B to E

 

[Perry Babin]

On this type of circuit, the most common failures (after the outputs, source resistors and gate resistors) are the 20 ohm resistors and the driver transistors (connected to the 20 ohm resistors).

Are you sure that there are no solder bridges or similar problems?

 

[mbates14]

Even more strange: I replaced the 20 ohm resistors with 220ohm resistors, and replaced the drivers again (last ones left in the package) and it works again. lol.....

 

[mbates14]

On this type of circuit, the most common failures (after the outputs, source resistors and gate resistors) are the 20 ohm resistors and the driver transistors (connected to the 20 ohm resistors).

Are you sure that there are no solder bridges or similar problems?

I know, i replaced them once. on both sides. including the 20 ohm resistors.

But if I use 220ohm resistors, the amplifier is happy. If i stick the 20 ohm resistors back in, it blows the drivers out again.