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Old 6th June 2011, 02:36 PM   #1
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Default Stumped on RF Punch 100 DSM amp - help

New to the board, but lurking for while trying to find solution to my problem. I have a RF Punch 100 DSM amp. Great little amp. Unfortunately, it powers up but i get no sound. I ordered new all mosfet chips and replaced the BUZZ11's and IRF540's. now i get a very faint audio sound out of of the speakers. in order to hear it i have to put the speaker to my ear. I also ordered the power mosfet chips (L7815CV, VC7915CT, IRF540, and U1610) but have not replaced them as the amp does power up. Wondering if anyone can lend some advice.

Thanks in advance.
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Old 6th June 2011, 06:06 PM   #2
kds9591 is offline kds9591  United States
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If the amp didn't draw excessive current your output and driver transistors are most likely ok. If you have a signal generator and ocilloscope you should trace the input signal forward from the RCA inputs. The amp probably has a defective op amp or may be missing one or more of the supply voltages because of a open trace or bad solder joint.

If one channel works or at least works better use that channel to compare waveforms and voltages to the defective channel. You can pinpoint problems rather quickly with this technique.

Good luck, keep us posted on your progress.

Last edited by kds9591; 6th June 2011 at 06:13 PM.
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Old 6th June 2011, 06:17 PM   #3
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Thanks for the advice/response kds9591.

Unfortunately, the only measuring device I have is a FLUTE MM. No signal generator or ocilloscope. Is here a way to achieve similar testing results with a MM? I have to admit that this is my first attempt at troubleshooting/reapiring an amp. I've installed many remote starters, stereo systems and even replaced IC hips in projection TV's. I'm familiar with soldering/desoldering, etc. I'm not afraid to get in and do the work, just need a bit of guidance.
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Old 6th June 2011, 06:32 PM   #4
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Is there any black corrosion between the capacitors on the preamp board behind the RCA jacks?
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Old 6th June 2011, 06:53 PM   #5
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I don't believe so. I'll check when I get home in a few hours - had to step out. I previoulsy checked all Capacitors. None swollen nor burst and contacts seemed clean both top side of board and bottom side.
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Old 6th June 2011, 10:22 PM   #6
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Just checked, no black corrosion. trying to figure out how to load a picture....
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Old 6th June 2011, 10:25 PM   #7
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testing pic loading...

Click the image to open in full size.

Last edited by m109ner; 6th June 2011 at 10:50 PM.
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Old 6th June 2011, 10:57 PM   #8
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I've never seen that board with large SMD capacitors in place of the standard, leaded film capacitors. I don't see any corrosion.

Start with the basics...

Do you have both positive and negative rail voltage on the output transistors?

Do you have both positive and negative regulated voltage on the power supply pins of the audio op-amps?

Does operating any of the switches or potentiometers through their entire range make a difference?
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Old 6th June 2011, 11:29 PM   #9
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Please bare with me a bit I am some what of a noob with the the terminology. I did check the voltage on the power supply pins (middle pins) all two read 12+ V, one read -12V, the fourth read 0. How do I check the rail voltage on the output transistors? With or without the amp connected?
Very faint sound coming out of the left channel speaker. I have to put it up to my ear and listen closely. adjusting the left gain potentiometer does increase it slightly (still need to put it to my ear to hear it) reducing it decreases the sound. No audio whatsoever from the right channel.

thanks
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Old 7th June 2011, 06:21 PM   #10
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anyone else that can help a brother out.

thanks in advance.
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