Rockford Fosgate 800.4 - Distortion Ch RR

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Witwe

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Joined 2010
DC Voltage with speaker connected:

RL - 11,1mV
RR without Q316 - 2,1mV
RR with Q316 - 438mV
LF - 5,3mV
RF - 1,5mV

AND:

I found out that the amp also produces clean audio when removing Q317! (Q315 and Q316 in circuit)
When I have tested this the first time, I have stopped with Q316 :( sorry for that
 
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Perry Babin

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Joined 2003
bcae1.com
Remove D301, D303, Q315, 316 and 317. Also remove the corresponding components from one of the other channels and compare the resistances in the two channels. Start with all of the resistors connected directly to these components.

This was done before but (at least some of ) the listed components were in the circuit. Since there doesn't seem to be any logical way of tracking down this problem, we'll have to do it the hard way.
 
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Witwe

Member
Joined 2010
Do you really mean D301 or D302?

Here are the readings with D(3/4)01, D(3/4)02, D(3/4)03, Q(3/4)15, Q(3/4)16, Q(3/4)17, R(3/4)45 and R(3/4)58 removed.

R336 - 0,2
R337 - 6,8
R338 - 6,7
R339 - not installed?!
R340 - 90,6k
R341 - 997
R342 - 994
R343 - 39,55k
R344 - 0,0
R345 (out) - 39,53k
R346 - 994
R347 - 10,11k
R379 - 6,7
R380 - 0,2
R381 - 549,2
R387 - 4,9k
R388 - 5,0k


R436 - 0,1
R437 - 6,7
R438 - 6,6
R439 - not installed?!
R440 - 92k
R441 - 988
R442 - 982
R443 - 39,2k
R444 - 0,0
R445 (out) - 38,16k
R446 - 998
R447 - 10,15k
R479 - 6,7
R480 - 0,1
R481 - 548
R487 - 4,9k
R488 - 5,0k

there seems to be no difference between the RR and RL channel.
But some measurements won't fit the values of the resistors. (but it is the same in both channels)
 
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Perry Babin

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Joined 2003
bcae1.com
Yes. I meant D302.

Since the amp works perfectly with the protection circuit defeated, the output transistors aren't likely to be the problem. At this point, however, I wouldn't rule anything out with this amp.

Have you been cleaning the board thoroughly after each time you solder the components or is it covered with flux right now?

If it's not clean, clean it thoroughly with a toothbrush and acetone to see if that makes a difference. Sometimes overheated flux can become conductive and cause problems. You'll have to reinstall parts (including Q316 and R345) to see if it's working properly.

Is this you amp? If so, is it your only amp?

If it's yours and it's your only amp, the best option may be to leave R345 out (the rest of the parts in) and use it like that. It will defeat the DC offset protection, so you should take that into consideration if you decide to do this.
 
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Witwe

Member
Joined 2010
normally I clean it after every soldering, but at the moment there is some flux arround Q315, 316 and 317.
I will clean it and test it out...
would it help to change every smd resistor in this channel?
or can it also be a dried out cap?
or maybe d302 itself?

this is the amp of my brother, but I would like to let the protection circuit disabled to be my last option.
 
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Witwe

Member
Joined 2010
another question that confuses me....
the problem channel is the rear right one.
but in the schematic it is printed as the rear left?
why is there RR- and RR+ printed on the right-middle site of the schematic on page 5?
And what is "LR-" between R345 and R358?
is that really connected to the negative rear left output connector?
can the problem be on that site?

(when the amp was in use before, it ran in bridged mode)
 
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Witwe

Member
Joined 2010
Hey Perry,

this amp makes me go crazy.
I have cleaned the amp and soldered everything back in place.
I have renewed R366 and R349, R345 and R358.
Also I have changed Q305 and Q306 because I have lost the originial installed ones.
And I have interchanged D301 - D309 with the 4series channel.

Now the sinewave lookes good at the scope with and without load connected
(I don't know why because all the old resistors are measured to be good)
An externally hosted image should be here but it was not working when we last tested it.

Also the bias pot increase the current draw.
BUT:
when I increase the volume it lookes like this at the 3 and 4series channel!
(the scope was not centered)
An externally hosted image should be here but it was not working when we last tested it.


But on the 1 and 2series channel, I can increase the volume to max without loosing a clean signal.

Is this a powersupply issue from the 3/4series channel? (because it also makes some hissing noise from this direction when increasing the volume)
 
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Witwe

Member
Joined 2010
I have found it!
after soldering everything back in place I had accidentally set the HP crossover.
At Fullrange and LowPass, everything is working great,
but with HighPass it lookes like above.
and with the volume a litte higher like this:
An externally hosted image should be here but it was not working when we last tested it.


Because both, the 3 and 4 series channel are affected, it would be a global problem, wouldn't it?
it looks bad even if I change the crossover frequency.
 
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Perry Babin

Member
Joined 2003
bcae1.com
Do the other channels remain clean with the crossover set the same way?

It could be global or it could be that the same defective or wrong parts were installed in both channels if both channels had the same work done to them.

Does the signal look clean coming out of the last op-amp in the circuit for channels 3 and 4?
 
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