Rockford Fosgate T1500-1bd - no output, no protect, no smoke - diyAudio
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Old 29th March 2013, 06:47 PM   #1
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Default Rockford Fosgate T1500-1bd - no output, no protect, no smoke

Hi Folks, checking out a Rockford Fosgate T1500-1bd.
It just stopped playing. No protect light, no smoke, no fuses blown. It appears to turn on normally, just no output.

I checked the outputs (IRFP3415) and the supply fets (75344g), all good.

The rails read +32 and -40 at CR1004 and CR1005.
After you turn it off the pos rail runs up to 77volts or so, while the neg rail quickly drops from the -40 to 0.

The low voltage supply seems kind of funny - at the rectifiers (CR1000-CR1003) the output is plus/minus 26.8 volts, with the LM317 reading +14volts and the LM337 -15volts.

The lm337 heatsink seemed to get really hot really fast, and somethings warm on the subboard next to it (left most board)...

Does anyone know what the rails should be?

I have a schema for a Power 2004 T10001bd. Does anybody know if its close?

I have to run out for a minute, but I'll remove the subboard when I get back I guess as there's no access to it for metering, etc.

Also, this amp has aluminum panels instead of the normal thermal boards....?

So, any ideas on where to start?
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Old 29th March 2013, 07:45 PM   #2
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Confirm that the regulator transistors Q2000, 2001, 2010, 2012 have the correct output voltage (-6, +6, +10, +10 respectively).

Check the solder connections on R2035 and make sure that R9 isn't broken from the board.
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Old 29th March 2013, 08:18 PM   #3
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Also check both 5110 ic's to make sure they are not shorted or leaky.

U2002 and U2000 I believe they are.
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Old 29th March 2013, 10:45 PM   #4
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Hey Perry, you should add a section to your tutorial on these...
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Old 30th March 2013, 10:42 AM   #5
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Due to a lack of demand for the tutorial, it's unlikely that I will be doing many more updates. Email me if you any other questions regarding the tutorial.
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Old 30th March 2013, 12:31 PM   #6
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Default checking trans Q2000, etc

Quote:
Originally Posted by Perry Babin View Post
Confirm that the regulator transistors Q2000, 2001, 2010, 2012 have the correct output voltage (-6, +6, +10, +10 respectively).

Check the solder connections on R2035 and make sure that R9 isn't broken from the board.
Okay, on the four transistors:
Q2000 (-6.7)(-22.5)(-6.1)
Q2001 (6.8)(17.8)(6.2)
Q2010 (11.8)(17.8)(11.2)
Q2012 (11.8)(17.8)(11.2)

B+ is 12.0

R2035 and R9 good.

I went through it after measuring and cleaned up a lot of really bad looking (cooked dry) solder.
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Old 30th March 2013, 03:57 PM   #7
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You have to measure the rail voltage with the two probes on the center legs of the rectifiers (no probe on ground).

This amp uses metal heat spreaders with an insulating coating. There should be one behind all of the output transistors. Do not let the transistors touch the heatsink.

The diagram that you have may be good enough to give you some idea of what the circuit is but it's not close enough for most components.

Don't remove anything yet.

Do you have an oscilloscope?
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Old 30th March 2013, 06:29 PM   #8
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Default How to test 5110 for leakage?

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Originally Posted by seankane View Post
Also check both 5110 ic's to make sure they are not shorted or leaky.

U2002 and U2000 I believe they are.
The 5110s are U2000 and U2002,but I couldn't find a datasheet for them. What are they and how should I test them?
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Old 30th March 2013, 06:48 PM   #9
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Default Rail voltage

Quote:
Originally Posted by Perry Babin View Post
You have to measure the rail voltage with the two probes on the center legs of the rectifiers (no probe on ground).
Ok, the rail measurement is about 20. As I apply/remove Remote it pops up to seventy for just a moment then comes down just as fast.

Quote:
Originally Posted by Perry Babin View Post
This amp uses metal heat spreaders with an insulating coating. There should be one behind all of the output transistors. Do not let the transistors touch the heatsink.

Do you have an oscilloscope?
No scope at the moment. I have an old pc I use as a sound card scope, just can't measure DC.

If I feed it some audio, can I rule out the preamp, x-over etc?

What is the function of the left most card?

Imma head over to bcae and brush up on class D.
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Old 30th March 2013, 09:27 PM   #10
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In general, soundcard scopes are only good for audio. They can't be used for troubleshooting the class D circuits or the power supplies without a LOT of guesswork.

The card near the SMD regulators is the audio PWM generation circuit.

I think the input to the audio PWM card is one of the two pins at the back end of the card.

Did the amp go into protect mode?
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