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Rockford Fosgate 250m2, badly beaten up
Rockford Fosgate 250m2, badly beaten up
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Old 11th July 2018, 09:52 PM   #41
manninen is offline manninen  Finland
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seems to be so.

i have measured somethings which i understand and im capable of. (not much tools)
mainly working areas ive touched, i need more time with this thing and need to measure few things which popped up my mind today.

im far from pro as you see
but yeah, really thought it was bad TO92 cause it measured so much different
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Old 11th July 2018, 10:05 PM   #42
motronix is offline motronix  Israel
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To fix this amplifier you must be pro and with good knowledge at Rockford Fosgate products. this amplifier is sophisticated and not easy for who didn't work with this amplifier before.
if you have the schematic for this model and you understand the diagram i hope you will fix it. you have DC at the output terminal and i am not sure you are search the problem at the right place so far
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Old 12th July 2018, 02:05 PM   #43
manninen is offline manninen  Finland
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Quote:
Originally Posted by Perry Babin View Post
Im really in dead end.

Q401, Q403 and Q404 are off board, DC is 0.4V, i think this is lowest number with this thing.

if i put Q403 and Q404 on board 42V kicks in, allways pair, dont know which one does it.

You said earlier check all transistors on board, measured (with my vbe matcher) and even changed few without result.

anything i can measure with multimeter?
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Old 12th July 2018, 11:27 PM   #44
Perry Babin is offline Perry Babin  United States
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Check every transistor and resistor shown in the image below.
Attached Images
File Type: png Clipboard03x.png (80.8 KB, 26 views)
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Old 13th July 2018, 05:27 AM   #45
manninen is offline manninen  Finland
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Gonna re-do that again.
This time gonna change those q424 425 to new ones. and iron them down.

Friday 13, is it my lucky day?
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Old 13th July 2018, 09:21 AM   #46
manninen is offline manninen  Finland
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resistors ok, new transistors ironed in, contact measured that solders are okay.

Click the image to open in full size.
bounces around, buzzes sometimes and then there is -42V
Q401 is not on the board.

i think next step is to try all four factory transistors
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Old 13th July 2018, 03:19 PM   #47
manninen is offline manninen  Finland
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im gonna take different approach. And explanation why i thought one TO92 was broken.

Click the image to open in full size.
them factory Q408, 407, 406 and 405
there is one guy who looks different.

and my vbe matcher results.

Click the image to open in full size.
one Q405, or MPSA06 pulls 3,49V voltage difference by its own
Click the image to open in full size.
add second and its 16,6mV difference
Click the image to open in full size.
Q408 or MPSA56 pulls 3,3V
Click the image to open in full size.
add the different looking guy and its 1,138v difference, not good, right.
Click the image to open in full size.
but thing is new MPSA56 i got can pull only 1,662V by it self
so new MPSA06 are 3,4V range. But paired withing 2mV

my transistor "matcher"
this is my tool, so is measuring vbe waste of time?


amp has now all parts in exept Q408 Q407 Q406 and Q405. dc rests pretty much dead zero
can i measure something from these empty holes?

just my thoughts

Last edited by manninen; 13th July 2018 at 03:27 PM.
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Old 16th July 2018, 10:36 AM   #48
manninen is offline manninen  Finland
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did some measurements that Q405-408 has connections.
I dont know was it mistake to turn amp on without these four components cause all components are now on board and amp does not react turning bias pot any more.

Is it still check all transistors on board?
Havent heard that buzzing sound anymore and no wandering DC so some component is now really broken.

Gonna get some lunch and start to compare components between channels
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Old 17th July 2018, 11:47 AM   #49
manninen is offline manninen  Finland
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factory Q424 Q425 Q404 Q403 on board and looks ok so far.
But if that different looking guy Q407 is on board i get -42v, it pass "universal meter transistor test" but if i change Q408 Q407 to new ones which i bought and leave Q406 Q405 factory i get 500mV DC.
i have feeling these four have to be similar.

Maybe i just have bunch of parts non interchangeable?

i still have to figure out why bias aint working
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Old 18th July 2018, 03:36 PM   #50
Perry Babin is offline Perry Babin  United States
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Until you reinstall Q401, the bias circuit won't work.
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