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Old 18th December 2007, 04:43 AM   #11
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It's essentially the same thing. It's best to use a signal source with its ground connected to the same ground as the amplfier. Having an isolated ground can cause you to miss some problems. Also, some amps don't react well to isolated grounds and it can cause you to chase problems that aren't there.
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Old 18th December 2007, 04:55 AM   #12
shagone is offline shagone  United States
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that's exactly what i have noticed. i think i will dig out a decent old car head unit to use as my bench source. is that what you would reccomend or is there something more flexible? i also have a variable frequency sine wave generator that has a ground lug. should that be grounded to the chassis of each amp i test or directly to the power ground input?

Sorry for the thread jack Scanlines but it is along the same lines i think
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Old 18th December 2007, 05:05 AM   #13
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A head unit will certainly work. I use an old home receiver as a signal source. The chassis ground of the signal source needs to be connected to the ground terminal of the power supply you use to power the amplifier. You should fuse the shield ground for the signal source with a 1 amp fuse. This will help protect the signal source from amplifiers with shorted transformers and for the times when you allow the RCA shield contact a power source.
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Old 18th December 2007, 05:14 AM   #14
shagone is offline shagone  United States
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great advice! i have had a couple of amps that sent a very loud feedback into my test speakers when hooked up to my old DJ pre-amp/mixer that was running to a home cd player. i did not have the chassis ground of the signal source connected to the ground terminal of the power supply I use. could it have been a shorted transformer or the ungrounded signal source? i think the amps in question were both older japan made kenwoods for some reason. luckily my setup had some king of protection circuit and once i reset everything it still played on other amps.
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Old 18th December 2007, 06:47 PM   #15
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Perry;

Using the working voltage model that you were so kind to provide, now, has got me scurring to try to find data on KPC127B chip (IC303). I believe it to be an opto isolator (8-pin dip) I just need to know the set up of that IC. The Soundstream schemo is kinda non-descript.

Here's what I found; Most of the voltage readings on my amp
are within .6 volt of the model except 2 ....the comp (pin 9)of IC301 ( PWM) chip and pin 6 of IC303.

The comp pin should be at 2.93v but, mine reads 5.64v the reading I should have for pin 6 of IC303 is 2.386v instead of 5.48v. looking at the schem. one of the collectors of the opto pak (pin 6) is keeping the comp pin up to 5v.

I'm trying to figure out which pins of the KPC127B (IC303D) is the led that's cutting off that transistor. this could lead me directly to the cause of all this misery. Datasheets for the KP.... seem a bit hard to find. Still looking.

BTW, the speaker output neg. is at 218.2 ohms of RCA shields.


Shagone;

Perry is right on the money.
I used to use only an isolated "home" cassette deck for a signal source. It was okay for most purposes but you could easily miss problems like the one I'm having with this 1500D. Or chase problems that really don't exist. That's why I now use mainly a head unit or a variety of sources if there are any questions.

I'm trying to get to the bottom of this on the Soundstream, (with much assistance from Perry). I did have another problem like this once. It was an MA Audio. Did the same thing. Turns out it was a bad drain insulator on one the power supply mosfets. Made the whole amp case +12 volt hot !
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Old 18th December 2007, 07:09 PM   #16
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As far as I know, the dual opto-coupler in this datasheet is the same as the ones in the amp.

http://media.digikey.com/pdf/Data%20...Fs/LTV-8x6.pdf


How can you have more than 5v on pin 9? Isn't it driven from the 5.1v reg of the 3525?

The 2.931v was probably only accurate for the amp I used. The ratio of windings on the transofrmer and the rail voltage would require different voltage on the comp pin.
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Old 20th December 2007, 07:36 PM   #17
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Thanks for the datasheet on the opto.
I think either the config. is different on the KPC127 or it's bad.

The static test shows the diode between pins 3 and 4 might be leakey. It's associated collector goes to the comp. pin of the 2535
which IS clamped to the 5.1v refference, but through R309. I'm not sure why there is and extra .45 volts on the opto side of that resistor. Another reason I'm suspecting it. Next, I'm going to pull the opto and check it out of the circuit.

I'll let you know.
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Old 20th December 2007, 08:52 PM   #18
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Fortunately, you have another identical one you can pull and compare to the suspect one.
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Old 30th December 2007, 12:31 PM   #19
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Perry;
This KPC127 tests okay out of the circuit.

Furthermore, the mysterious ...the .45 above 5.1v reference voltage on the comp pin of the 2535 is still there with the KPC gone.

I began looking at IC307 (labeled IC305 on the pcboard)
I see its a programable zener reference that drives the LED on the KPC. it's cathode is sitting at -28.8v.

I don't know if that is where it should be.
Right now, I've got the suspect portion of the KPC out of the circuit and the amp behaves exactly the same.

I'm begining to get a feeling that my problem is somewhere between the power supply primary and secondary. Something off-set or leakey between 12V DC and +/- 56V and it's ground.

The RCA shields are where they should be, 220 ohms away from ground. I've checked all the RC pairs connecting the different grounds together. They're fine.

The guy who owns the amp says it worked fine in his other car.
He took it out, the amp laid around for several months and he had it installed in his new car it went into protect when RCA's are connected.

I'm going to examine these power supply voltages closely.

What is the purpose of the "VPPD" voltage ??
Thx,
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Old 30th December 2007, 01:36 PM   #20
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The VPPD is the high side driver voltage. It has to be above rail voltage so the drivers can drive the high side N-channel FETs to the rail.

As long as the 431 reference has 2.5 volts between the anode and reference, it's doing its working properly.
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