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Keatah 8th June 2011 09:32 AM

a little help with fixing an alpine mrp f300 & parts please
I have an Alpine MRP F300 amp.
It was working perfectly last night, and today I power up the system and it makes a spitting/farting noise that dies out.

I tested the head unit, and there seems to be no problem there. I checked for shorts with the speakers, and everything checks out at 4 ohms. There is good clean power going to the amp. And it powers on with the head unit correctly, with the accessory line.

Now, I took apart the amp and found a shorted SK 2SA2151 transistor, and a partly shorted SK 2SC6011 transistor, in-circuit resistance measurements. I compared them to another channels output stage and these are, without a doubt, shorted! The 2151 doesn't get hot, the complimentary 2SC6011 gets blisteringly hot! But no smoke or burned casing.

There are two smaller transistors/mosfets KD600KY and KB631KY nearby which seem to be drivers. The KD600KY gets extremely hot, but not burned or smoking.

I also checked the power supply output rails and everything seems to be in order there.

My question to you folks is where can I get these parts? And should I be looking at anything else?
SK 2SA2151 and SK 2SC6011
KD600KY and KB631KY

Perry Babin 8th June 2011 03:21 PM is an Alpine parts distributor. If you want the original replacement parts, contact them.

For generic replacements, the FJA4313 and FJA4213 should work for the outputs. For the drivers, the KSA1220A and the KSC2690A should be good subs.

Keatah 8th June 2011 09:21 PM


Originally Posted by Perry Babin ( is an Alpine parts distributor. If you want the original replacement parts, contact them.

For generic replacements, the FJA4313 and FJA4213 should work for the outputs. For the drivers, the KSA1220A and the KSC2690A should be good subs.

Excellent! Thanks so much for the subs. Once I get them installed I'll report back. I did find original parts for the drivers the, 600 and 613, from Sanyo.

Perry Babin 9th June 2011 02:32 AM

Although it's probably not important on this amp, the 2sd600 and the 2sb631 with the K suffix are rated for higher voltage and more difficult to find. The subs I listed for the drivers are high voltage drivers capable of replacing the d600 and b631 with the K suffix.

Keatah 9th June 2011 07:09 AM

It might not make much of a difference. I would be guessing that the gain curve could be just a little different. I did see some minor variances in Collector Current. I would need to look at the graphs in more detail to be certain. That in and of itself probably wouldn't make a difference in sound quality in an automotive environment.

I could see this making a difference if you bridge the channels, maybe. Once I get the amp up an running I'll compare the specs and differences between the original parts and subs for a leisure activity.

Keatah 9th June 2011 07:32 AM

BTW: this is about as far as I go for fixing this amp. Anything more and I don't think I'd have the patience to tear deeper into the circuit and work through everything. Not right now.

So the order of the day is to get the 4 transistors swapped and then go from there. I plan on getting this done before Saturday night, but there is a concert rolling into town, so I have only till late Saturday morning, really.

So far, I first took out the PCB and put all the hardware aside and labeled where the screws go and that sort of thing. There is absolutely no visual cue as to the 4 bad parts. All the traces look good and no overheating signs, so on and so forth. Magic smoke still inside!

I could take pictures of what's going on, but someone else has already posted several pix of this amp. I really like how each part's designation is silk-screened!!

Keatah 10th June 2011 12:31 PM


Here are pictures of the amp, and what I have done so far.

I have decided that I want to get this amp fixed, regardless of my time. I used to play quite a bit with electronics and build projects, and part-time troubleshooting a few years ago. I remember as a kid (in the 1970's) building those RadioShack project kits with the spring terminals, like the Solar Lab kit and the VHF aircraft receiver, and the 150-in-one kits. But longafter since then I got into other technical hobbies. But fixing this amp has now become a "fun project".

Recapping: (no pun intended)
Originally this is what happened. I turned on the amp(system) a few nights ago, the speakers sputtered and farted and the amp seemed to draw a lot of current where the main 50A or 75A fuse at the battery threatened to explode. Once I realized there was a problem I disconnected the amp. For testing purposes I only powered it up for a minute or two afterwards, that's when I noted the hot transistors. Speakers still stuttering and farting. Also the heatsink of the amp seemed to be getting ready to run warm with no input signal. I'm sure if I left it on for a long time it would have blown up and exploded!! I rechecked the speakers to be absolutely certain they weren't shorted internally or to chassis ground - ok good.

Now, inside the amp..
Here's what I found: Channel - 1 seemed to be partly shorted out. In anticipation of completing repairing my amp (alpine mrp f300) I got a head start and carefully removed the suspect components. Solder sucker, minimal heat, etc.. I made some out of circuit measurements and this is what I got.

The 2151 output transistor is completely shorted 1.2 ohms across any combo of 3 pins. A diode drop of 0.595V is nowhere to be seen here. This transistor never got hot, apparently.

The complementary 6011 output transistor seems to check out good. 0.595 and 0.596 drops, and if I use the ohm function I get 2.7M and 2.8M ohms. It is also possible to get open circuit conditions if I reverse the leads. Everything says this transistor checks good! It also happened to be the one that was getting smoking hot too!!

I also checked out the kd600k and kb631k driver transistors. They are good also. I get very similar readings of 0.598 to 0.604 diode drops, and right around 3.8M to 4.09M ohms with the resistance scale. These all seem to be in the right combinations and, again I can get open circuit readings if I reverse the leads and try other combinations. So these seem fine according to basic transistor testing techniques. Also, strangely enough, it was the kd600k that was blasting hot!

(So let me get this straight, one of the output transistors pushes the speaker cone up, and the other one pulls it down. They both tie into some monster-sized 0.1 ohm resistor. And both output transistors are biased slightly on. So that's class AB then!)

Anyways, are there any additional measurements I can make now? Prior to replacing these parts and prior to powering it up for the first time? In retrospect, I don't fully trust my "power-supply measurements" I made earlier on, because the amp had shorted components. Also, I'm not 100% sure what the supply is supposed to read!?!
Is it safe to power up the amp with Channel-1's output and drivers out of circuit?
Would the protection circuit kick in?
Would the other channels 2-3-4 work?

For fun, I measured the dual-diode packs FRH20A15 and FCH20A15 and got a 0.2V drop and open-circuit, depending. Seems good to me. I also checked the other KD600K and KB631K bjt's seemingly in the power supply circuit, they check good just like the others.

There seems to be a PWM controller here too. It is a 16-pin pso-smt case, what a fascinating read the datasheet is! And the markings are ((TEXAS INSTRUMENTS)) 87C4CCM TL494ID.

I didn't measure anything related to FET's because I hear that using a basic voltmeter can blow them up but good! I used a FLUKE-79 DMM for all my measurements. I can also replace those tiny SMT parts if needed.

My girlfriend, who is a wizard at finding things on the internet (but knows nothing of electronics!), found me all original parts from the links you guys provided. And it only cost about 15.00 with shipping, they should be here today or tomorrow. I plan on replacing all 4 transistors; 1 is shorted, and 2 others got way too hot. I don't know what conditions the 4th one experienced when the amp blew up.

Dr Zeus 10th June 2011 01:42 PM

Hey Keatah,

I'm working on an MRV-F300S in the other thread. Im not 100% positive but these amps could be similar with the difference being MRV vs MRP. If you need anything let me know because mine works and plays but just has some odd CT voltage offset.

What voltage are you reading referencing amplifier ground to the positive and negative voltage rails? Mine is offset by ~20vDC and will not power up without protection circuits removed. It does play though :)

Dr Zeus 10th June 2011 01:45 PM

You know what... our amps are not even closely similar after I looked at your pictures.

Keatah 11th June 2011 03:52 AM

wow what a difference in design and layout and probably capabilities, with just a different letter in the model number. I'm learning mostly as I progress through this repair. I can't help but think that there will be more than just a shorted transistor in my repair though.

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