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Old 12-16-2016, 05:02 PM   #1
TheDragon
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Default Pioneer HU RCA issue (tried some fixes)

Hi all, as per title, I have the common pioneer car stereo RCA buzzing issue.

I recently acquired a fully functioning HU from ebay, model :KEH-P8400R.
Its rather an older unit that plays cassettes but has CD control and/or AUX input. Perfect for my carPC, plus I wanted the retro look and my favorite old Pioneer logo and font.

Anyway, it was functioning. I had it temporarily connected up, drove with it, partially inserted and sounded great, with all the glorious tape hiss.
Then the next day, I came to fully fitting it. Everything was wired up properly and then the dreaded RCA buzzing (alternator whine) was heard.

I tested with a friends spare HU, the RCA cables to the amp are fine. I checked my amp ground connections, worked fine. No noise with tester HU.

I then set about grounding the pioneers RCA shields (a typical fix for possible blown pico fuse). This shielding repair did not work.
As my system is older, I cannot find an pico fuses and there are no mention in the service manual.

I really want his unit working, it was a hard find on ebay. Can anybody shed any light what could be the issue. Are there some hidden fuses or other component that could be blown and defunct-ed the RCA connections ?

The service manual can be found here:
https://www.manualslib.com/manual/95...eh-P8400r.html

I really do hope someone can help.
Appreciate it
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Old 12-16-2016, 05:13 PM   #2
madan1
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Default Re: Pioneer HU RCA issue (tried some fixes)

After all you have tried, this might sound stupid, but try connecting the head unit's chases to the amp's chases with a wire.
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Old 12-16-2016, 05:30 PM   #3
TheDragon
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Default Re: Pioneer HU RCA issue (tried some fixes)

Quote:
Originally Posted by madan1 View Post
After all you have tried, this might sound stupid, but try connecting the head unit's chases to the amp's chases with a wire.
Hmm interesting idea. The amp is in the back, but there is a wire in the middle of the RCA cables, I could use that. I'll try this tomorrow and report back. thx
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Old 01-09-2017, 05:44 PM   #4
TheDragon
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Default Re: Pioneer HU RCA issue (tried some fixes)

Quote:
Originally Posted by madan1 View Post
After all you have tried, this might sound stupid, but try connecting the head unit's chases to the amp's chases with a wire.
Sorry about delay in replying. Got busy in holiday season and family things.
I did as you suggested. It may have helped somewhat, though I can still hear the alternator whine at low volumes, but once volume is lifted and car is moving, not much can be heard. Its more prevalent with car idling than when in motion.
I guess my only choices are for complete reduction. Get stereo repaired or use RCA isolation devices ?

thx for suggestion
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Old 01-09-2017, 07:01 PM   #5
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Default Re: Pioneer HU RCA issue (tried some fixes)

When you were testing it the first time and you did not hear the alternator whine, were both units metal bodies bolted to the car chassis? You can try RCA isolator as you suggested.
Or something like this?
https://www.amazon.com/PAC-CSS12-Pas.../dp/B000CEDZBA
BTW, how are the audio RCA cables routed? Close to the noise source?
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Old 01-13-2017, 05:04 AM   #6
TheDragon
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Default Re: Pioneer HU RCA issue (tried some fixes)

Quote:
Originally Posted by budm View Post
When you were testing it the first time and you did not hear the alternator whine, were both units metal bodies bolted to the car chassis? You can try RCA isolator as you suggested.
Or something like this?
https://www.amazon.com/PAC-CSS12-Pas.../dp/B000CEDZBA
BTW, how are the audio RCA cables routed? Close to the noise source?
Thanks for the assist.

No, the units were not bolted per se, but both units have good solid grounds connected (Which I did check were still good as a maintenance procedure before connecting the HU and amp).

In all honesty, the HU was just replacing the old dead one. The harness was wired in and soldered with heat shrink. All the return speaker/RCA cables were in the same route functioning fine under previous unit.

Thanks for that optional part link.
I did also find this on youtube:

https://www.youtube.com/watch?v=jbv9PUC0xPk

From which would indicate I need the ferrite core filter.
I have a few salvaged ferrite coils laying around, so simple enough to make and test.
That part you suggested perhaps does the same thing?

On a side note. I see that you have a few topics in your signature.
The inverter one caught my eye. Was wondering what you knew about inverters in relation to electroluminescent displays?

This Pioneer unit has such a display. There is a distinct buzz coming the display and the wired interverter block.
Some say it's part of the units characteristic, but one would doubt that Pioneer would pass such engineering with such obvious buzzing sound.

I had thought about replacing the electroluminescent sheet behind the LCD, as the brightness seems dim.
The inverter itself looks clean and tidy. No bad or loose solder joints.
Not even sure if it also needs replacing too. Do these 'wear' out?

Thanks once again
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