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Punch 75HD Only One Channel Plays
Punch 75HD Only One Channel Plays
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Old 13th October 2012, 05:12 PM   #1
CuriousAudio is offline CuriousAudio
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Default Punch 75HD Only One Channel Plays

Only the right channel plays. If i connect the left channel (-) to the right channel (-), i also get music.

All voltages are good at the points labeled on the schematic. I do not have a scope. Any Suggestions?

I have replaced all supply/output transistors and the HBPIM
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Old 13th October 2012, 05:48 PM   #2
seankane is offline seankane  United States
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Location: Washington State
Confirm all the source resistors are within tolerance.

Confirm there are no cold solder joints on the speaker plug.

Confirm the rca input jack is not loose internally, sometimes you have to solder the shield to the mounting frame.

If you are using the factory harness bypass the fuses in the speaker plug to confirm there is not a bad connection there.

Confirm there are no issues on the HB-PPM or the HB-POM.

Does the channel bias properly?
Pyramid 52 Amp Power Supply----Fluke 787 Processmeter----Tektronix 465 Scope----Velleman HPS40 Scope----Soldering Iron----Desoldering Iron----Hejet HJ 500-S Heatgun----DM4070 Digital LCR Meter----Propane Torch
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Old 13th October 2012, 05:57 PM   #3
CuriousAudio is offline CuriousAudio
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Ok, I'll do what you suggested

Can you tell me how to bias correctly? I read up that rockford wants 4 to 5 mv across the source resistors, but i get nowhere near that with my red and black leads on both sides of the source resistors and meter set to mv
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Old 14th October 2012, 04:39 AM   #4
Perry Babin is offline Perry Babin  United States
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Join Date: Nov 2003
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If your 12v power supply has an amp meter, you can set it as is shown in the following demo.

Setting it with the voltage across the 0.1 ohm source resistors requires that you monitor the voltage and slowly turn the bias pots clockwise. This is done with no speaker load and no signal input. I feel that 4-5mv is too much and will make the amp run hotter than it needs to. It won't harm anything but it doesn't need to be set that high. 1mv is generally good enough.

If the right channel plays but it doesn't play bridged, there is likely a bad connection between the speaker and the terminal block on the amp. If it has brown/black fuse holders, they have a tendency to become intermittent as the terminal in the holder is pulled too deeply into the holder. I think this is why it was suggested that you bypass the fuse holders.
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Old 18th October 2012, 06:16 PM   #5
CuriousAudio is offline CuriousAudio
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Problem Found: The left board HB3 (HB-POM) has one small transistor missing on the board. That's why I don't get sound from that side. Now i need a new HB-POM...
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