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NAD 304 still has problems after replacing faulty resistors and relay
NAD 304 still has problems after replacing faulty resistors and relay
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Old 14th February 2020, 12:58 AM   #11
EstueraIV is offline EstueraIV
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Originally Posted by Junm View Post
I also had repaired this model with the two 47k 1/2 resistor busted (open). after replacing this it turns on red then green. when off it turns red again but its normal. Had you tried playing music with it? when relay activates it means no dc out.

well before I messed it up even more yesterday, it played music, but the left channel had very little bass, I think the right channel sounded normal, I forgot how it normally sounds but it seemed fine. It's gone completely in protection mode now that I shorted something while trying to measure the DC offset
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Old 14th February 2020, 08:00 AM   #12
Junm is offline Junm  Philippines
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ohhh thats bad...when you fix the problem try playing music without the preamp, remove the jumper for pre out at main amp in. if still unbalanced the problem is on the amp. check the balance pot and input caps.

Check your output trannies if they still alive..
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Old 15th February 2020, 05:17 AM   #13
Ian Finch is offline Ian Finch  Australia
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At this point, it would be wise to get professional help. Yes, anything can be fixed provided we know how the circuit should work, how to assess what is needed, including test instruments and genuine spec. parts, in order to replace any damaged ones and have good spares.
As mentioned earlier, this isn't an average amplifier. It operates with dual pairs of power rails where the higher rails are only switched in according to power demand. To understand and address its common problems requires a bit more than poking about, as in the simple designs we are familiar with here and in most older commercial products where there are no tricky power circuits that need an engineer to analyse.

If you are causing more damage as you test a circuit (yes, I've done that!) it's time to stop and consider what your knowledge and experience so far has taught you. We need to study more than just a schematic before diving in with probes, unaware of the dangers of slipping and shorting circuits and voltages that can destroy even the largest semis in a flash. Still, there are several aids to testing with meter probes that should be in use as appropriate. You may also need three hands and two pairs of eyes to use a meter whilst making adjustments if you are trying to hold standard probes in place at the same time. No wonder we have problems
1. Sharp, hard probe tips to penetrate and "grip" in solder joints.
2. Clip leads (alligator or crocodile clips on either end of insulated wire, about 30cm. (not great but cheap)
3. Hook probes - the normal probe leads are replaced by leads with a spring loaded hook at the tip, chosen to be small enough to reach into closely spaced wiring and make reliable contact whilst your attention is on the meter. (variable quality and sizes, many too big, expensive etc. and some very cheap but too flimsy to last long)
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Last edited by Ian Finch; 15th February 2020 at 05:21 AM.
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