HIfonics BXi 1606 voltage float sound issue - diyAudio
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Old 27th July 2009, 09:30 PM   #1
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Default HIfonics BXi 1606 voltage float sound issue

I have a BXi 1606 that had a high pitched whine coming from the speakers. Replaced the HIP4080a and got rid of the whine, but there is about a 1.6v float on the output and there is a sound like an am receiver listening to sunspot activity if you listen closely to the speaker.
Some background on the unit: It was previously repaired and has FQP65n06's in power supply (is this original?). the ground ref trace that goes around the HIP4080a is lifted and burnt but not severed.
Here are some pics:

Any ideas?
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Old 27th July 2009, 09:37 PM   #2
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The noise is likely because they don't synchronize the power supply frequency to the output carrier frequency. It's normal. People with amps, new out of the box have had the same complaints.

If you measure the DC voltage from the negative speaker terminal to the positive speaker terminal (after the relay engages) and have more than 0.025v DC offset, adjust VR10 until it's 0.025v or below. Do this with no audio input.
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Old 27th July 2009, 09:50 PM   #3
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Thanks, I did adjust the Bias pot but could only get it to .9v, also seeing quick warmth from tip41 bias? chip.

Sound does seem more excessive than even John Studley would allow. Said with all respect.

Could it be the TC4013BP Flipflop, causing the frequency mismatch and bias voltage? It looks like it was warmed by the trace almost failure.
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Old 27th July 2009, 09:54 PM   #4
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I doubt that the flip flop is causing any problems.

The TIP41 is likely part of a voltage regulator.

What's the voltage across ZD1?
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Old 27th July 2009, 10:00 PM   #5
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-1.46 -> 5.35 Are the dc voltage to ground readings
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Old 27th July 2009, 10:05 PM   #6
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Place the meter probes directly across the zener.
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Old 27th July 2009, 10:10 PM   #7
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Sorry about the rust. It is 6.82v
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Old 27th July 2009, 10:19 PM   #8
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If I'm not mistaken, it's a 6.2v Zener. At 6.8v, it's out of tolerance. I don't remember having any at 6.8v but I know when they get to ~7.5v, they cause problems. I'd replace it and try adjusting the offset again.
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Old 1st August 2009, 01:43 AM   #9
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Tracked down 6.2V zener. Got 6.5v and still float.
Parts order came in and replaced 4080a with new intersil, dc float went away and I could zero.

I have a couple of more questions.

How much warming should I expect out of 4080a in early low power testing?

The AM Noise is really noticeable and I have not heard it this loud out of new amps before, 20yrs experience, former Hifonics rep.
Could it be something with one of the lm393N's, I can physically touch the case of one of them and sound changes character?
Sorry, No scope, it sold with the store.

I still had the noise with the last NJM4558L pulled out of circuit to isolate from preamp. (one of the legs broke and replaced with NJM4558LD, will this be OK?)

BTW Thanks again for the advice.
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Old 1st August 2009, 02:08 AM   #10
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The 4080 will get warm but shouldn't be too hot to hold your finger on.

Earlier, you stated that you had to have your ear near the speaker to hear it. If it's significantly louder, there may be another problem. Is it louder now?

What's the circuit board designation for the op-amp that you pulled?

If your amp has yellow filter capacitors near the B+ terminal, they sometimes fail. I've seen quite a few fail and they looked perfectly fine (no visible evidence of damage). If you parallel another relatively large capacitor across the B+ and ground terminals and the noise changes significantly, those caps may be defective. When the capacitance goes very low, the amp will generally refuse to start. I'm not sure what happens when they are simply below rated capacitance.

I can't find the datasheet on the LD version of the op-amp. I don't think there will be a significant difference.
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