Rockford Fosgate Punch 600a4

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objext

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Joined 2005
LM833s are

U300
U301
U400

U100
U101
U200

I went ahead and got voltage off all the remaining TL072s and they were all basically the same (except the one I have pin 4 & pin 8 lifted).

R50: 0.60v
R51: 0.60v
R43: 0.54v
R44: 0.53v

But this is with U402 pin 4 & 8 lifted. Should I resolder those and check again?
 
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objext

Member
Joined 2005
Reconnected U402 pin 4 & pin 8:

R50: 0.60v
R51: 0.60v
R43: 0.62v
R44: 0.61v

Another thing I just discovered is that testing from B- to the RCA connections I get 0.58v on everything except the left rear outside (negative/sleeve).

edit: okay, that's just a broken rca lead
 
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O

objext

Member
Joined 2005
Before doing that I took readings off the LM833s just in case. They seem pretty consistent except for Pin 1 & Pin 7 on U101 & U301 reading a bit lower than the rest.

U200
Pin 1: 0.60
Pin 2: 0.60
Pin 3: 0.59
Pin 4: -12.11
Pin 5: 0.59
Pin 6: 0.60
Pin 7: 0.62
Pin 8: 13.76

U400
Pin 1: 0.58
Pin 2: 0.59
Pin 3: 0.58
Pin 4: -12.12
Pin 5: 0.58
Pin 6: 0.59
Pin 7: 0.60
Pin 8: 13.72

U101
Pin 1: 0.50
Pin 2: 0.61
Pin 3: 0.61
Pin 4: -12.13
Pin 5: 0.61
Pin 6: 0.61
Pin 7: 0.50
Pin 8: 13.74

U301
Pin 1: 0.49
Pin 2: 0.59
Pin 3: 0.60
Pin 4: -12.12
Pin 5: 0.60
Pin 6: 0.60
Pin 7: 0.49
Pin 8: 13.72

U100
Pin 1: 0.58
Pin 2: 0.58
Pin 3: 0.58
Pin 4: -12.13
Pin 5: 0.58
Pin 6: 0.59
Pin 7: 0.60
Pin 8: 13.74

U300
Pin 1: 0.58
Pin 2: 0.58
Pin 3: 0.58
Pin 4: -12.13
Pin 5: 0.58
Pin 6: 0.59
Pin 7: 0.59
Pin 8: 13.72
 
O

objext

Member
Joined 2005
I don't have any, but I do need to make an order soon for some other parts, so I could get some.

Before then, would it be a good idea to lift, for instance, R50 & C11 (and maybe R51 & C12), to isolate that entire set of opamps? I guess I'm not sure what we're looking for by only lifting the power supply to any given opamp, or replacing one we've already lifted the power pins to.
 

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objext

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Joined 2005
My main concern is the extreme heat of the regulators, being, or having been, hot enough to do damage to the board around them.

Is it normal for all the MPSA06 and MPSA56 to get hot at idle as well? Not 200° hot, but as much as 120° give or take.

I don't think the caps are heating, I just thought it might be necessary if lifting the resistors to try to isolate one section that might be causing an excessive load.
 
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Perry Babin

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Joined 2003
bcae1.com
Are you referring to the transistors connected to the bias transistors?

The bias setting would likely make a difference with that. I don't think that if the various supply voltages are near what they should be that you would have 4 channels defective in the same way.

The two groups of op-amps are drawing approximately the same current. Look at the drop across the 20 ohm resistors. There may not be a problem but I don't remember the op-amps getting hot.

I looked at the photos on the ampperformance.de site and the regulators were showing signs of heating the board (bottom photo). I don't know how much use the amp had compared to yours. In Germany, they likely had cooler temperatures than we do.
Rockford Fosgate Punch 600a4 - AMP Performance
 
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objext

Member
Joined 2005
Yes, such as Q108 & Q109. Maybe I'm just being paranoid, but even considering the mehsa pads on other models it doesn't seem like the regulators get nearly as hot at idle.

Ah, yes, same voltage drop, I see what you mean.

I guess I am concerned that this is too hot, considering it gets over 200° even with low 70° ambient temperature. Here's a close-up of mine - looks like the PCB has even cracked a little.
 

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objext

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Joined 2005
Yes, this is my amp, but I just recently got it so I haven't used it in a car environment yet. I own most of the other models from this era and have never seen this kind of specific heating from other models like the 400a4, 800a4, 800a2, 500a2, etc. Eventually I will sell some off, but I'd feel uncomfortable selling this one as good working condition considering how hot it's getting. I've tried to ask some of the other guys in various Fosgate or old school car audio groups, and most people I've talked to seem to also think it's too hot.
 
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objext

Member
Joined 2005
Yes, the thought crossed my mind to increase the heatsink area, but I still thought they were heating more than other models and would like to know why.

I will try that tomorrow. I hope you don't mind my intermittent responses - I really do appreciate your help.
 
O

objext

Member
Joined 2005
Reconnected Pin 4 & Pin 8 on the U303 TL072C. Removed R50, R51, R43, R44.

At 13v input, LM317 getting up to about 182°, LM337 up to about 158°, with the following readings:

LM317
In: 28.6V
Out: 14.3V
Adj: 13V

LM337
Out: -12.7V
In: -28.6V
Adj: -11.3V


I also checked voltage drop across the following since they are in series with the regulator output also:

R170: 0.38v
R171: 0.38v

R270: 0.38v
R271: 0.38v

R370: 0.38v
R371: 0.38v

R470: 0.39v
R471: 0.38v


Increased the supply voltage to 14.4v and start to hear coil whine/hiss or whatever it is - not sure. I noticed it's actually audible even after starting up. Loud at first, then quiet once the amp starts.

Regulator temperatures actually go down to about 169° each, but readings remain the same. At this voltage Q6 & Q8 power supply fets also start to heat compared to Q5 & Q7 (about 115° compared to 100°).

Q108/Q109, Q208/Q209, Q308/Q309, Q408/Q409 heat to the 120-130° range.
 
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