# Understanding the Pico fuse and RCA connections...



## xtremevette (Apr 14, 2011)

Ok so first to familiarize those who don't know what a Pico fuse is, it is a very small fuse that Pioneer uses on most of its head units as well as DSP units that is unserviceable and soldered onto the circuit board.

What happens is when the unit is powered on and someone disconnects the RCA's the fuse blows. This causes grounding issues on the RCA's/circuit board and produces a realm of noise problems ranging from buzzing to high pitch squealing noises. The problem is usually resolved by simply wrapping wire around the RCA metal grounds/output jackets coming out of the source unit and then having those tie to a good chassis ground close by. _(from my understanding of this)_

So with that...my only question is _WHY OH WHY WOULD ANYBODY UNPLUG THEIR RCAS FROM A SOURCE UNIT WHILE IT IS ON??????_

Is it just me or doesn't this just seem like common sense of duh....what NOT to do?


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## minbari (Mar 3, 2011)

considering that most RCA outputs have low output impedance and short circuit protection, my question is:

WHY OH WHY WOULD PIONEER PUT AN SERVICEABLE FUSE THAT BLOWS IF YOU LOOK AT IT CROSSEYED ON THIER PRODUCTS?

When troubleshooting sometimes taking an RCA off is necessary. you shouldnt have to power the whole thing down to do it. its just bad engineering.


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## xtremevette (Apr 14, 2011)

minbari said:


> considering that most RCA outputs have low output impedance and short circuit protection, my question is:
> 
> WHY OH WHY WOULD PIONEER PUT AN SERVICEABLE FUSE THAT BLOWS IF YOU LOOK AT IT CROSSEYED ON THIER PRODUCTS?
> 
> When troubleshooting sometimes taking an RCA off is necessary. you shouldnt have to power the whole thing down to do it. its just bad engineering.


Iam all for troubleshooting but I can't think of one single instance that would dictate that you HAVE to have the power on while you disconnect the RCA's. More convenient YES. But not a necessity. Sure it's a pain to keep walking back to the receiver to power it down but that's a lot safer to do in the first place whether we are talking about RCA's or just components in general. You start plugging stuff in and out while anything has power to it...we'll your playing with fire. Iam almost thinking that maybe it should of been called something else...when people hear FUSE, they figure it should be serviceable. I think it is on the board only as a safeguard so that you don't fry the rest of the circuit board. But hey what do I know...that's just my .02.


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## minbari (Mar 3, 2011)

you are not playing with fire with an RCA cable. the micro-amps that are capable of being produced by the pre-amplifier are not going to start any fires.

my point is if you forget to turn it off and pull a cable, it shouldnt fry your $900 HU. its stupid.


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## xtremevette (Apr 14, 2011)

minbari said:


> you are not playing with fire with an RCA cable. the micro-amps that are capable of being produced by the pre-amplifier are not going to start any fires.
> 
> my point is if you forget to turn it off and pull a cable, it shouldnt fry your $900 HU. its stupid.


Ok maybe saying playing with fire you took too literally. What Iam pointing towards is that with electricity running through anything, you start unplugging stuff....you take a chance...plain and simple. I get what your saying...but would it be any different if you forgot to not short the speaker wires to chassis? or forget that the power wire goes to the + side and the negative wire goes to -? Not trying to be a smartazz just saying...you make it sound pretty simple about ooops I forgot to unplug them and that shoudn't fry my $900 unit, but at the same time there are plenty of other oop's that would fry it as well or fry any $1000-$10,000 amplifier too.

If anything Pioneer should at least have it clearly written in their manual "DO NOT DISCONNECT RCA's while the unit is on. Failure to do so could result in malfunction or damage. It could be a flaw but I just don't see it, it's been on most Pioneer units now for almost 2 decades.


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## minbari (Mar 3, 2011)

ya, but there is no way to put RCA cables on backwards, lol. no other company I know of in home audio or car audio will be damaged if you pull an RCA cable and mov e while the unit is turned on.

if its a safety feature its a bad one. no one else seems to be having the problem they are attempting to avoid, so it must not exsist.


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## xtremevette (Apr 14, 2011)

minbari said:


> ya, but there is no way to put RCA cables on backwards, lol. no other company I know of in home audio or car audio will be damaged if you pull an RCA cable and mov e while the unit is turned on.
> 
> if its a safety feature its a bad one. no one else seems to be having the problem they are attempting to avoid, so it must not exsist.


Well I will agree with you that to us, the consumer, their safety feature is a bad one. For us it does suck when the thing dies because of this reason. For them...hmm who knows could be a good cash flow item that forces one to send their "broken unit" in for replacement or repair. I dunno. I think I read one guy on here was successful in bypassing the thing on his head unit. He just ran a new trace around it. I wouldn't do it with my head unit but it's cool knowing it could be done.


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## jp88 (Jun 25, 2007)

The purpose of the pico fuse is to protect the head unit in the case of a bad ground conection on the connected power amp which will cause some amps to draw current through the rca cables through the head unit.

Incendentally the other way to cause a pico fuse to blow is by having a poor ground connection to your amp.

ps Im not saying that this protection was well implemented, just pointing out its purpose.


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## ceri23 (Aug 10, 2012)

Mine blew on my 880 and I never once unplugged an RCA while the unit was on. I see no reason for it. Besides, since the fix is to ground the shielding on the RCAs to the head unit chassis, all that tells me is that it's a ground transmission line. Why would you fuse a ground instead of just making it permanently grounded to the chassis internally? Are they so concerned that consumers will open up their head unit's internals (thereby voiding the warranty anyway) and rerouting transmission lines to a line carrying voltage? I've never heard a good explanation for why it exists in the first place. RCA's aren't carrying enough voltage to spark anything.


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## xtremevette (Apr 14, 2011)

This would be a great one for a Pioneer rep to jump in on!


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## thomasluke (Jun 10, 2011)

xtremevette said:


> This would be a great one for a Pioneer rep to jump in on!


But they don't exist on here....DAMN!


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## RoyalBlue08 (Mar 28, 2012)

I blew my headunit out 3 times already from this ********, now I know what the problem is. I just sent my avh 8400 out for repair again today,


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## mfarlow (Nov 27, 2009)

I've had this happen 3 time now, and not once was it due to swapping live RCA inputs.

First time was due to a bad terminal connection on my Alternator. Nothing I could have detected on my own, but had to send the HU back for service because of it. First time repair was covered under warranty.

Second time, I have no idea. It just blew, maybe a loose RCA connection to the rear of the HU, not entirely certain, but once again it's out for service. Ths time it cost $150.

Third time, it popped after replacing a fuel pump. No idea how this could have had any impact at all on the HU, but it did. Out again for service, another $150. This time Pioneer service claimed a bad ground at the HU and did not service the PICO fuse. When I received it still had the same alt whine, so back it went for a 4th time. Again they didn't even check the PICO fuse and claimed to have repaired a bad chassis ground. It still has the alt whine. 

All together I spend almost $400 getting this thing repaired. That's more than I paid for the HU.

I'm not about to send it back to them again. Maybe if I find someone who can actually fix the PICO fuse issue for me I'll start using the HU again, but at this point I'm pretty much done with Pioneer specifically because of their decision to use PICO fuses.

I should comment that I have tried 3 other HU's from other manufactures in this vehicle with the same components and wiring, and not one has ever experienced any sort of alternator whine like this unit.


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## WTF1978 (Apr 12, 2012)

is there any way to tell if the pico fuse is shot without hooking up the head unit? I'm going to look at a p880prs and want to make sure it works like it should before i buy it


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## minbari (Mar 3, 2011)

if the pico is blown, then the RCA shield would not be grounded. use a DMM and measure. (this is why grounding the RCA shield solves the problem in most cases)


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## WTF1978 (Apr 12, 2012)

minbari said:


> if the pico is blown, then the RCA shield would not be grounded. use a DMM and measure. (this is why grounding the RCA shield solves the problem in most cases)


Thanks. I don't have a lot of experience with a DMM so can you explain exactly how to check?


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## minbari (Mar 3, 2011)

set your DMM to "ohms"

put the black lead on ground
Put the red lead on the RCA shield(ground)

should read less than 1 ohm.


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## WestCo (Aug 19, 2012)

minbari said:


> considering that most RCA outputs have low output impedance and short circuit protection, my question is:
> 
> WHY OH WHY WOULD PIONEER PUT AN SERVICEABLE FUSE THAT BLOWS IF YOU LOOK AT IT CROSSEYED ON THIER PRODUCTS?
> 
> When troubleshooting sometimes taking an RCA off is necessary. you shouldnt have to power the whole thing down to do it. its just bad engineering.


Pioneer wants you to buy a new deck every 2-3 years.
To answer that question


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## ImK'ed (Aug 12, 2013)

Its plain bad design rcas can and do accidentley get unplugged sometimes


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## Jepalan (Jun 27, 2013)

IMO - The PICO fuse concept is a good idea, but poorly implemented by Pioneer - period. I tend to side with Minibar on everything posted here. I think the main theoretical (electronic design) reason for the ground fuse is to prevent large ground currents from destroying the head unit if a downstream power amp is poorly grounded. This is a real-world possibility worth protecting against.

If properly implemented, the ground fuse should *not* blow just from plugging/unplugging a 'live' RCA cable. Other manufacturers don't seem to have a problem with this. I don't think that is because they aren't protecting against large ground currents, I think it is because they have implemented a better solution.


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## HardCoreDore (Apr 30, 2014)

I know this is an old thread, but is it possible to damage a Non-Pioneer deck, or even an amplifier by "hot-swapping" RCA's? I've always done this over the years over many different systems, and I've not had any issues.


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## Victor_inox (Apr 27, 2012)

****ty design, maybe for reason. why not to use self resetting fuses instead, they probably a penny more expensive but can be tiny.


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## minbari (Mar 3, 2011)

Victor_inox said:


> ****ty design, maybe for reason. why not to use self resetting fuses instead, they probably a penny more expensive but can be tiny.


Or just buffer the output to tolerate shorting the rcas. We are not talking about alot of current here. I have never blown rca outputs in 20 years and I hot swap all the time


Victor_inox said:


> ****ty design, maybe for reason. why not to use self resetting fuses instead, they probably a penny more expensive but can be tiny.


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## HardCoreDore (Apr 30, 2014)

Ok, I just wanted some others with experience to validate what I already knew. I haven't owned a Pioneer since 1995, and I hated that deck. I guess that's why I never went back. Nowadays, though it seems like they are the only major manufacturer that makes quality audiophile head units. I guess some of the higher end Alpine is ok...

I may have to build a car-puter, next time.


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## DrFred (Jan 19, 2013)

Hope this is on topic enough - does anyone have any experience with using a ground loop isolater like this Parts Express piece - Axxess AX-AGL 610 2 channel GLI to cure a Pioneer Pico issue ? Thanks , Kelly


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## HardCoreDore (Apr 30, 2014)

DrFred said:


> Hope this is on topic enough - does anyone have any experience with using a ground loop isolater like this Parts Express piece - Axxess AX-AGL 610 2 channel GLI to cure a Pioneer Pico issue ? Thanks , Kelly


Not I, but imho ground loop isolators are a waste of money. It's much better to just eliminate the ground issue. 

If you have a blown Pico fuse there are several threads on here showing how to fix it.


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## minbari (Mar 3, 2011)

Ground loop isolators have thier uses, certainly not a watse if you are isolating grounds. Look inside pro-audio gear , they are littered with isolation transformers.

They will not fix a bad ground though. The blown pico-fuse disconnects the ground from the RCA. It will not fix the noise problem. If it is blown, you can fix the issue by replacing the fuse (or jumpering it) or by grounding the RCAs.


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## DrFred (Jan 19, 2013)

Thanks for the info - will try one of the other approaches and save some money by skipping the GLI - Kelly


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