# Fix for Pioneer P99RS with blown "pico" fuse



## Jamse (Feb 14, 2013)

Hi everybody

A few weeks ago my P99RS started making some seriously loud and ugly noises. I already knew all about Pioneers usual error, the blown pico fuse. However, I'd read that the P99RS doesn't have one, so I was a bit surprised, since the noise I heard was exactly as the blown pico fuse noise was described: combined alternator and random analogue noise, together with pops and bangs on turn on/off and source switching. 

It turns out it really doesn't have a pico fuse. But it has something similar, called a poly fuse (wiki: resettable fuse). It's name is miniSMDC075F/24 - google will get you a datasheet, if you're interested, but here's the basics: It's a component with a very low resistance (in this specific case 0.09 ohm), which increases in resistance when it becomes hot from high currents, to a maximum of 0.29 ohm, thus descreasing the current. The idea is that the decrease 'saves' the component from frying, making it a 'resettable fuse'. This of course is a step up from the pico fuse, but it will still fry if the current is high enough. 

This defect can easily be diagnosed with an ohm-meter. The resistance between the ground-pins (lower row) of the RCA-connector plug and the casing should be very close to 0 ohm. First measure the error of your ohm-meter by touching the two probes, and get a reading. Mine was 0.3 ohm (cheap thing from China). Then measure from the ground-pins to the casing - mine should have read 0.3-0.4 ohm, but it read 1.5 ohm. This means that any noise induced in the shielding now has a (1.5-0.3) 1.2 ohm resistance before it reaches ground, and not a direct link, as it should have. The 1.2 ohm is the result of several different paths through the entire main board, some of which are probably through some very noise sensitive circuitry, which is why the noise becomes so excessive. 

So I took it out of the car for further examining. I am no professional, but I do have some experience in electronics and general find-out-how-this-thing-works-by-taking-it-apart. Here's the basic disassemble procedure. I have attached some pictures to help you along.

1: Remove the top lid. It lifts off the back of the unit and is pulled away from the front. No screws.
2: Remove the CD-unit - it's held in place by 3 screws, two of which are hidden 'inside' the CD-unit, in the front end. There are two cables that must be disconnected: one normal, one flat. The flat cable is removed by pulling the two side tabs towards the cable, in a direction parallel with the board, releasing the lock-in, and then gently prying it out.
3: To remove the main board, do the following:
a) disconnect the plug for the front motorized mechanism.
b) remove the two screws, one in the corner near the antenna plug, and the other on the side from the outside, near the usb plug.
c) remove the bracket on the usb-plug side, covering the 4 mosfets(?) sticking out of the board. Not really sure if this is necessary, but it's easy, so...
d) un-twist the 3 twist locks.
e) unplug the flat cable that connects the front to the board, again by pushing the tabs towards the cable.
f) the black back of the unit is mounted on the main board, and comes of together with it. Once the above is done, the back of the unit can be lifted from the copper frame and pulled backwards out of it. Be gentle, it should come easily - if not, you've forgotten something.

On my unit, only copper plated screws needed to be removed. 

4: Turn the main board over and look for P551 written with white letters, close to the RCA-connector plug. This is the culprit. 

5: Un-solder it from the board. Strictly not necessary if it is completely burnt, but it may still be able to carry a current, so if it stays in place it could cause problems.

Measuring on the un-soldered component yielded various results, depending on where I put the probes. The component looks like it consists of 4-5 layers of some metal. Pressing the probes against the end sides, touching all the layers, gave close to 0 ohm. But when I pressed the probes against the buttom of the component, touching only where the soldering did, it showed the 1.2 ohms that I measured in the beginning. 

Solutions to this problem are open for discussion. I didn't want to test my SMD soldering abilities, so I down graded to Pioneer's cheaper solution: the pico fuse (which I had already bought a bunch of, before knowing of the existance of poly fuses). Since the placement on the board requires complete disassembly, I soldered two wires to the board with a female-plug on the end, where the pico fuse fits. This way I can change the it from the outside, should it ever fry again. 

I re-installed the radio, and ba-da-bing, noise gone


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## SkizeR (Apr 19, 2011)

good write up.


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## aztec45 (Jul 23, 2007)

Nice... Epic.... Didn't know p99rs had this problem too...


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## SkizeR (Apr 19, 2011)

im just wondering what caused it to go bad


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## Jamse (Feb 14, 2013)

SkizeR said:


> im just wondering what caused it to go bad


Excessive live swapping RCA's...before I knew anything about it.:blush:


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## TrickyRicky (Apr 5, 2009)

Jamse said:


> Excessive live swapping RCA's...before I knew anything about it.:blush:


:laugh:Lesson learn I assume. Always cut off your heat unit (or signal source) before swapping RCA's or leaving them unconnected without a protective sleeve on the ends.


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## subwoofery (Nov 9, 2008)

TrickyRicky said:


> :laugh:Lesson learn I assume. Always cut off your heat unit (or signal source) before swapping RCA's or leaving them unconnected without a protective sleeve on the ends.


Hot swap many times on my Eclipses and the 3 units I have never had any problem... Pioneer really needs to find a solution for that - especially for the price of that HU. 
Just imagine if they had that same problem on their $5k ODR units - I would be mad

Kelvin


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## captainobvious (Mar 11, 2006)

Thanks for the informative thread on the P99RS fuse fix issue. I'm having noise with mine as well and am going to check mine out. Can you tell me the size pico fuse you used for the replacement of the SMD poly fuse? Is it a simple resistor? (looks like it in the pics).

Thanks !!

-Steve


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## DBlevel (Oct 6, 2006)

I was about to comment in your thread Steve. I was having the same issue (alt whine) with my p99. Matt said he could fix the issue even tho it wasn't the normal or old style pico. I'm assuming he'll be doing the same or similiar to mine as above while he has it lol.


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## Kevin K (Feb 11, 2013)

Thanks for sharing.


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## DBlevel (Oct 6, 2006)

Well I was going to post a link to this thread but when I searched for it I seen he had already found it.


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## captainobvious (Mar 11, 2006)

DBlevel said:


> I was about to comment in your thread Steve. I was having the same issue (alt whine) with my p99. Matt said he could fix the issue even tho it wasn't the normal or old style pico. I'm assuming he'll be doing the same or similiar to mine as above while he has it lol.



I found a couple of oddities with mine. The first one I talked about in my thread (link below) was a loose ground connection to the P99RS wiring harness which I don't see a way to fix. The second is that my rca output bundle appears to have a slice into a couple of the jackets of the wires. Don't know where the hell that came from. Doesn't appear to go all the way to copper but it still isn't reassuring. I ordered both a new rca bundle harness and the regular power wire harness from Pioneer to replace these two items. We'll see if it makes any difference. Once I hear back from the OP about the fuse, I may swap out with his method as well.

http://www.diymobileaudio.com/forum...162874-loose-ground-wiring-harness-noise.html




.


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## DBlevel (Oct 6, 2006)

Might could see about replacing the RCA harness. I haven't looked close enough yet or tried but I've been told the harness can be removed I'm guessing similar to like the 880 RCA harness. 

As far as the loose ground in the harness you could always try to repin it in hopes of it getting a better connection.


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## captainobvious (Mar 11, 2006)

DBlevel said:


> Might could see about replacing the RCA harness. I haven't looked close enough yet or tried but I've been told the harness can be removed I'm guessing similar to like the 880 RCA harness.
> 
> As far as the loose ground in the harness you could always try to repin it in hopes of it getting a better connection.



Im not sure which tool to use for this type. I've done ones for DB type connectors, but this is smaller and I didnt see an easy way to get it out. I was wondering about connecting a ground wire to the chassis instead. There's that chassis screw on the back left corner that I could use. May try that and remove the ground connection from the harness...


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## captainobvious (Mar 11, 2006)

FYI-

This looks like the actual part for the P99RS:

MINISMDC075F/24-2 | MINISMDC075F Series 24 V 0.75 A 1812 Surface Mount Polyswitch Resettable Fuse | RAYCHEM - Future Electronics

MINISMDC075F Series 24 V 0.75 A 1812 Surface Mount Polyswitch Resettable Fuse

24V 0.75A 1812 surface mount polyswitch resettable fuse (minismd)
hold current 0.75A 
trip current 1.5A
MINISMDC075F Series 24 V 0.75 A 1812 Surface Mount Polyswitch Resettable Fuse - See more at: MINISMDC075F/24-2 | MINISMDC075F Series 24 V 0.75 A 1812 Surface Mount Polyswitch Resettable Fuse | RAYCHEM - Future Electronics
MINISMDC075F Series 24 V 0.75 A 1812 Surface Mount Polyswitch Resettable Fuse - See more at: MINISMDC075F/24-2 | MINISMDC075F Series 24 V 0.75 A 1812 Surface Mount Polyswitch Resettable Fuse | RAYCHEM - Future Electronics


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## captainobvious (Mar 11, 2006)

Well...I installed a DC-DC converter between the battery and the P99RS so that it gets its power and ground direct from the units isolated power supply. (I have it set for 13.5vdc output which it measured close to when I connected it).
The noise was still there. I took apart the P99RS and tested with the DMM on both sides of the _*soldered*_ poly fuse (P551 on the back of the board) as shown and I'm seeing between 0.1 and 0.2 ohms resistance. Could this still be the issue or does that indicate that the problem lies somewhere else? Does it need to be measured unsoldered?

To be clear, I've already tested the rest of the signal chain by disconnecting the rcas from the head unit. (The noises all went away, dead quiet)

Any ideas?


Thanks again, I appreciate your assistance.


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## Jamse (Feb 14, 2013)

captainobvious said:


> Well...I installed a DC-DC converter between the battery and the P99RS so that it gets its power and ground direct from the units isolated power supply. (I have it set for 13.5vdc output which it measured close to when I connected it).
> The noise was still there. I took apart the P99RS and tested with the DMM on both sides of the _*soldered*_ poly fuse (P551 on the back of the board) as shown and I'm seeing between 0.1 and 0.2 ohms resistance. Could this still be the issue or does that indicate that the problem lies somewhere else? Does it need to be measured unsoldered?
> 
> To be clear, I've already tested the rest of the signal chain by disconnecting the rcas from the head unit. (The noises all went away, dead quiet)
> ...


0.1-0.2 is still more than what the poly fuse should be, which is 0.029 if I remember correctly. It's practically too small to measure without specialized equipment.

I tried to measure on the board when the poly fuse was unsoldered, and there was no connection at all. So your poly fuse is not as bad ad mine was, but it may not be in perfect shape. 

There may be a problem with using a DC-DC converter. I don't know much about it, but if the amplifiers do not share ground with the HU, I think the noise could somehow find its way into the signal. And the DC-DC converter may de-couple the two grounds.

I don't like the poly fuse. As mentioned in the main thread, I measured mine to something less than infinity, implying that it might still work. But it was broken, no doubt about it. So it's a difficult component to deem defective. If you are sure the DC-DC converter does not pose a problem, I would try unsoldering the poly fuse and either solder on a new one, or make a plug for a replaceable pico fuse.


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## captainobvious (Mar 11, 2006)

Jamse said:


> 0.1-0.2 is still more than what the poly fuse should be, which is 0.029 if I remember correctly. It's practically too small to measure without specialized equipment.
> 
> I tried to measure on the board when the poly fuse was unsoldered, and there was no connection at all. So your poly fuse is not as bad ad mine was, but it may not be in perfect shape.
> 
> ...




I installed the DC-DC converter after the fact but it didn't really make much of a difference. I desoldered the poly fuse and put a piece of small wire in place to test. Same noise.
I put an inline ground loop filter on a pair of RCA outs from the P99RS and the noise was 99% gone on those outputs. There's definitely something going on with the P99RS/ground. (I also tried moving my ground location to the engine bay opposite where the stock ground was made and that didn't make any difference either.

Next I'll try grounding the RCA shields to see if that does anything. It may in fact just be something else going on inside the P99RS that needs fixing.


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## lynchknot (Sep 27, 2014)

I had a similar issue with alternator whine with another brand. Grounding the shield of the RCA line level outputs to the chassis of the radio worked.


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## zero9 (Sep 24, 2014)

NEVER ground it directly without fuse.


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## captainobvious (Mar 11, 2006)

captainobvious said:


> I installed the DC-DC converter after the fact but it didn't really make much of a difference. I desoldered the poly fuse and put a piece of small wire in place to test. Same noise.
> I put an inline ground loop filter on a pair of RCA outs from the P99RS and the noise was 99% gone on those outputs. There's definitely something going on with the P99RS/ground. (I also tried moving my ground location to the engine bay opposite where the stock ground was made and that didn't make any difference either.
> 
> Next I'll try grounding the RCA shields to see if that does anything. It may in fact just be something else going on inside the P99RS that needs fixing.



Didn't realize that I never came back to update this post. The problem I was having was due to two things. First- the RCA output harness had some of the wires scored, looked like a razor blade or sharp piece of metal came in contact with them. 
The second issue was that I had a loose ground wire in the P99RS wiring harness.

I ordered new replacements for both of these harnesses direct from Pioneer and that solved the problem I was having. No issue with the deck itself


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## lynchknot (Sep 27, 2014)

zero9 said:


> NEVER ground it directly without fuse.


I don't understand. This is what many car audio shops and websites suggest.


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## captainobvious (Mar 11, 2006)

lynchknot said:


> I don't understand. This is what many car audio shops and websites suggest.



There is nothing wrong with it. Consider that the chassis of a head unit is grounded to the cars chassis and the RCA shields are grounded to the head unit chassis (or should be).


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## lynchknot (Sep 27, 2014)

captainobvious said:


> There is nothing wrong with it. Consider that the chassis of a head unit is grounded to the cars chassis and the RCA shields are grounded to the head unit chassis (or should be).


The way it's worded sounds like (to me) he's saying there should be a fuse between the chassis and the RCA shield preout jack.


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