Soundstream PCA1500D Qwerky - diyAudio
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Old 13th December 2007, 07:19 PM   #1
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Default Soundstream PCA1500D Qwerky

Hello; This one is a bit strange. Let me know if anyone has seen this before...

When this Soundstream PCA1500D is powered up, it will instantly go into protect mode as soon as you connect the RCA's.
When I got it on the bench, I measured a 5volt offset voltage between the RCA shields and 12volt DC ground. ....huh?

Voltage rails were normal. No excessive current draw. Resistors, caps and op amps looked OK in the input section, so I called Soundstream and they told me to disregard the 5 volt offset and look for leakey mosfets(output or power supply)

I removed all the audio output mosfets. It still when into protect. I removed all the power supply mosfets, and installed 2 new ones
(one on each bank) just to run the amp. ....No go.

Then, I replaced all 4 rectifiers, ESR'd caps in the power supply and output rails. No change.

I'm getting ready to swap out the plus and minus 15V regulators next although, there is a clean +15 and -15 volts present.
I will forge ahead.
TIA for any advice scan
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Old 13th December 2007, 09:16 PM   #2
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Is there a 220 ohm resistor near the RCA jacks?

If so, is it within tolerance?
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Old 14th December 2007, 11:30 AM   #3
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Yes,
there is a 220 ohm right next to the rca pack, R101 and it is within tol. (219.5 ohms)
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Old 14th December 2007, 05:39 PM   #4
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Is the signal source grounded to the ground terminal of your power supply?

If you plug the RCAs in 'before' you power it up, does it go into protect?

If you unplug the RCAs from the amp, what's the resistance between the secondary ground and the chassis ground?
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Old 15th December 2007, 03:03 PM   #5
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The signal source is NOT grounded to the ground terminal of the power supply.

When I plug the RCAs in 'before' I power it up, IT DOES go into protect Mode.

When I unplug the RCAs from the amp, the resistance between the amp's RCA shields and the chassis ground is 258.2K

Between the test deck's RCA shields and chassis ground is .888meg

(Both of these resistance readings took some "settle time"
I assume due to the capacitance in the circuits)

I really appreciate yout time. ....BTW, The amp didn't go into protect when I use a "home" cassette deck for a signal source.
DC issues or what ???
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Old 15th December 2007, 09:54 PM   #6
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What happens if you ground the RCA shields of the amplifier to chassis ground?

What are you using for a signal source (other than the home cassette deck)?

If it's a head unit, how does it operate without being grounded to the ground terminal of the 12v power supply?
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Old 17th December 2007, 05:37 PM   #7
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>>What happens if you ground the RCA shields of the amplifier to chassis ground?<<

If I ground the amp's RCA shields to the 12Volt supply negative, it immeadiately goes into protection. When I un-ground the shields. from the the supply negative, it comes out of protect and the green "happy" led lights up again

>>What are you using for a signal source (other than the home cassette deck)?<<

I am using a set of older Pioneer head units: either the DEH-205 or a DEH-10.

>>If it's a head unit, how does it operate without being grounded to the ground terminal of the 12v power supply?<<

I switched the DEH-205 to another (isolated) DC supply and the amp did not go into protect
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Old 17th December 2007, 06:43 PM   #8
shagone is offline shagone  United States
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So Perry and Scanlines what do you think was going on here? What can we learn from this? Do different amps behave differently with home equipment and car head units. i have used anything from home tuners to dj preamps to playstation one's and even car head units and tone generators for testing amps with varying results. some had more noise than others and some amps didn't seem to like my home preamp. what is the best signal source to use at home on my bench that will be compatible with most car amps out there? my guess would be a car head unit but what else works well and what should be grounded to what?

i must say my original sony ps one with removable rca's has a very powerfull and clean signal but it is very loud on most amps even with the gain all the way down and my wife doesn't go for that past 10pm.
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Old 18th December 2007, 03:37 AM   #9
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scanlines:
The following voltages are from a working amp (not a PPI). Check the voltages with and without the shield grounded to the ground terminal of the amp to see what changes.

http://www.bcot1.com/images/type2cla...rmation02a.jpg

You may want to confirm that the negative speaker terminal is within ~220 ohms of the RCA shield.


shagone:
I'm not sure what's going on here. The problem with the amp could be any number of things at this point.

The isolated signal sources are probably not causing it to go into protect because they're not dragging the shield ground to 0v (where it should be). When he plugs the signal source into the amp, the entire source unit's ground and power supply voltage are probably being shifted up 5v (with reference to the ground terminal of the amp).
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Old 18th December 2007, 04:38 AM   #10
shagone is offline shagone  United States
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kind of like using an ipod as a signal source where the ground is isolated because it is battery operated?
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