Help: Boss CE-3800D "Static and whining noise" - Page 3 - diyAudio
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Old 2nd March 2014, 01:19 AM   #21
Itsme is offline Itsme  United States
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Quote:
Originally Posted by laplace View Post
Well, you have a serious power supply problem, there's about 10V of crap coming through at ~100kHz. Given the asymmetry of the the waveform, I'm going to guess that the fault is with the latter part of the PSU switcher, i.e. after the switching transformer. I could be totally wrong here, but have a look for shorts (due to gunk from the exploded caps) and bad/open/shorted components (diodes, capacitors) in the rectifier+filter stages of the PSU.
Ok, I didnt notice this till just a bit ago, but the ground wire I hooked to the grounds on the probes has a voltage reading and is not the same as the B- terminal. Which I dont understand because it is a ground wire to the amplifier case. But now when I try and hook up the probes grounded to the B- terminal the voltage goes to high on probe 1 and off the scale on the oscilloscope. I can only go up to 10 volts on the oscilloscope. Not sure what to do to get measurement? Also I get -22.50 volts From B- to positive speaker wire, But just millivolts when its hooked up to neg speaker and positive speaker. Where should I connect the oscilloscope probe grounds? Is B- correct? And how can I adjust oscilloscope to measure over 10 volts? Autoset isn't doing it.
Thanks
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Old 2nd March 2014, 02:53 AM   #22
laplace is offline laplace  Australia
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Ignore B+ and B-, they're quite possibly floating depending on the amp's supply design, or at least not centred on "zero". The amplifier's case is probably a good bet, or maybe if you can find a track labelled "GND" on the circuit board. It's likely your amp has a 55V supply, which would put the speaker terminals at 22.5V each (wrt B-) with no signal, and they will probably swing symmetrically around that centre-point.

If you want to measure higher voltages, you can use a 10x probe.
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Old 2nd March 2014, 03:30 AM   #23
Itsme is offline Itsme  United States
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This is the ground wire I had connected to. It has GD marked on the board beside it. So where should I go from here? If I flex the board a little it does make a little difference in the static. So im thinking a loose connection maybe? Is there anythying else I can do to narrow it down a little?
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Old 2nd March 2014, 03:49 AM   #24
laplace is offline laplace  Australia
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You'd need schematics to do much more than guesswork.
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Old 2nd March 2014, 04:17 AM   #25
Itsme is offline Itsme  United States
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Im not going to find schematics on this, there has to be another way. I reconnected that ground wire and switched probe 1 to 10x and probe 1 is on the middle leg of outputs and probe 2 on pos speaker and this is what I got.
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Old 2nd March 2014, 11:54 PM   #26
Itsme is offline Itsme  United States
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I have gone through the board testing all diodes and resistors and they are all to spec's. Is there any way to bypass the inductor coil or replace with a similar inductor just to test for a few seconds to see if it is my problem?
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Old 3rd March 2014, 12:36 AM   #27
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Hello! Can you please take the waveform of the +- rail voltages? You can use the black wire hanging around on your amp as your reference.

Last edited by nonprof; 3rd March 2014 at 12:48 AM.
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Old 3rd March 2014, 01:05 AM   #28
Itsme is offline Itsme  United States
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Hello! Can you please take the waveform of the +- rail voltages? You can use the black wire hanging around on your amp as your reference.
Ok, Just to make sure Im hooked to the right places I took a picture of connections. Also do the settings look ok on the oscilloscope?
Thanks
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Old 3rd March 2014, 02:00 AM   #29
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Originally Posted by Itsme View Post
Ok, Just to make sure Im hooked to the right places I took a picture of connections. Also do the settings look ok on the oscilloscope?
Thanks
probe 1 is in the gate? and probe #2 is in the rail? either you may have problem.
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Old 3rd March 2014, 02:20 AM   #30
Itsme is offline Itsme  United States
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Originally Posted by nonprof View Post
probe 1 is in the gate? and probe #2 is in the rail? either you may have problem.
Probe 1 was connected to the drain or collecter of the irfb31n20dpbf and probe 2 was connected to the gate. I'm not really sure where to find rail + and -, everywhere I test I get AC voltage of around 60 volts.
Also probably a dumb question but should all the output transistors be the same kind or should they be half pnp and half npn types?
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