Rockford Fosgate 250m2, badly beaten up

[manninen]

seems to be so.

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

i´m far from pro as you see
but yeah, really thought it was bad TO92 cause it measured so much different

 

[motronix]

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

 

[manninen]

Link:
http://www.bcae1.com/temp/rockford - power250m2.pdf

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?

 

[Perry Babin]

Check every transistor and resistor shown in the image below.

 

[manninen]

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?

 

[manninen]

resistors ok, new transistors ironed in, contact measured that solders are okay.

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

 

[manninen]

im gonna take different approach. And explanation why i thought one TO92 was broken.

them factory Q408, 407, 406 and 405
there is one guy who looks different.

and my vbe matcher results.

one Q405, or MPSA06 pulls 3,49V voltage difference by its own

add second and its 16,6mV difference

Q408 or MPSA56 pulls 3,3V

add the different looking guy and its 1,138v difference, not good, right.

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

 

[manninen]

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?
Haven´t 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

 

[manninen]

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

 

[Perry Babin]

Until you reinstall Q401, the bias circuit won't work.

 

[manninen]

There is traces on both side of board on TO92´s but on board does not have sleeves to connect both sides.

i had to solder those properly on both sides. Thats why there was so random stuff going on.

channel works again and eight vbe matched transistors gives 16mV of dc out

 

[Perry Babin]

The sleeves are called vias or feed-throughs. They were damaged at some point when someone removed the transistors.

 

[manninen]

Could be so, this thing has many components changed all over the board. Just one different TO92 but all these holes does not feed through, other channels TO92's look untouched.

 

[manninen]

Qx24 and Qx25.

As my journey is this far im not gonna leave it to 16mV. (sure heat it up properly to see hot numbers later)
What is your opinion now when all transistors are sort of pairs, am i gonna just take just little bit stronger transistor to Qx25 Qx24? and if looking to that another channels, those hot TO92's does it matter for effiency or something else if there aint good pairs? i have all eight allready choosen, just thinking if i take short or long course. Change them all and then Q324 Q325.

In factory i bet they havent choosen any components, just hit them in from same batch

 

[manninen]

Took short course and changed Q325 and Q325 only.

dc´s around 6,4mV cold and after warming up ~9mV and ~13mV

slight blow to TO92 cluster and goes under 0mV.

I put outdoor temperature sensor between those and temp passed meters 70C max, so they run 70-80deg