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