Repair a KRK 10s Subwoofer - parts id

[GromTag]

OK. a moment to allow me to get my itinerary together and plot the board, that image helps a great deal. and as for the damaged tracks, yes sometimes they do lift, however, as long as they are up to the connection point solder patching is simple. Just requires a light scratching of the coating near the track point and then solder the new point with good part. I am going to provide images on this by using a junk board that I have parted out. If that would be ok? (on the how to repair those tracks)

 

[chinjazz]

OK. a moment to allow me to get my itinerary together and plot the board, that image helps a great deal. and as for the damaged tracks, yes sometimes they do lift, however, as long as they are up to the connection point solder patching is simple. Just requires a light scratching of the coating near the track point and then solder the new point with good part. I am going to provide images on this by using a junk board that I have parted out. If that would be ok? (on the how to repair those tracks)

Sure, I'd appreciate that. Conceptually all we're doing is laying down solder for continuity basically right?

I looked on the other side to follow where E goes, and it appears to go straight to the nearest blue resistor, then that connects to the other resistor, and then travels down the outside line, and straight to your "Or Like this" location...

 

[GromTag]

Bingo, this is an easy part, the E tracks do not go directly to signal processing other than the bad 3206 C. The collector goes to switch Q438. this is a signal switching transistor and the Panasonic is a very close switch replacement. the over all config does look to be an on statement switch to power part of the signal switching array for the power processing parts. As now I can see that the bad 3206 Emitter does not go anywhere other than the blue 68 Ohm resistor. Overall as long as Q444 is ok, the replacement should reactivate the amp and board.

Extra notes:

The replacement parts thus far are the Panasonic transistor 2SC1473A (Digikey)
the resistors at close as well are the two:
68 Ohm Mouser part 279-LR1F68R TE Connectivity brand
1K Mouser part 279-LR1F1K0 TE Connectivity brand.

the resistor leads can be carefully bent to get them to fit if they have more length than the originals by a margin oversized. The new transistors leads may be straight and require slight bending below the safe range limit at the bottom of the transistor itself. I can provide info on how to if needed.

And also for the thermal management. The NON conductive thermal grease that isolates the large switching BJT transistors from that aluminum block heat sink. I can provide assistance with that if needed as well.
The exposed metal backs are tied to usually the center pin on the transistor itself, therefor they need to be isolated from conducting to that heat sink.

As those two wires are not quite GND use but do provide a prevention from the switching parts from ringing back to the board via electric fields of varying ranges when switching on and off and producing a bad noisy board as a result (buzzing through the speaker at all times when powered on even if all parts are working correctly). A heat sink is needed for the speaker drivers, but not the noise overall, thus, just connect a common lead to it the companies say... It's a design thing.

to get an idea (if you don't know) of a transistors speed, the tone of a speaker requires a 2 way motion to produce a tone, fast operation. so the music is the speed of them operating push and pull for the drivers as example, just think drum soloist beating the drum fast enough to produce a solid tone, not a realistic ability, but the metaphor stands.

 

[GromTag]

getting a junk board out now and heating up the 15W iron as this would not require much heat.

 

[chinjazz]

Bingo, this is an easy part, the E tracks do not go directly to signal processing other than the bad 3206 C. The collector goes to switch Q438. this is a signal switching transistor and the Panasonic is a very close switch replacement. the over all config does look to be an on statement switch to power part of the signal switching array for the power processing parts. As now I can see that the bad 3206 Emitter does not go anywhere other than the blue 68 Ohm resistor. Overall as long as Q444 is ok, the replacement should reactivate the amp and board.

Extra notes:

The replacement parts thus far are the Panasonic transistor 2SC1473A (Digikey)
the resistors at close as well are the two:
68 Ohm Mouser part 279-LR1F68R TE Connectivity brand
1K Mouser part 279-LR1F1K0 TE Connectivity brand.

the resistor leads can be carefully bent to get them to fit if they have more length than the originals by a margin oversized. The new transistors leads may be straight and require slight bending below the safe range limit at the bottom of the transistor itself. I can provide info on how to if needed.

And also for the thermal management. The NON conductive thermal grease that isolates the large switching BJT transistors from that aluminum block heat sink. I can provide assistance with that if needed as well.
The exposed metal backs are tied to usually the center pin on the transistor itself, therefor they need to be isolated from conducting to that heat sink.

As those two wires are not quite GND use but do provide a prevention from the switching parts from ringing back to the board via electric fields of varying ranges when switching on and off and producing a bad noisy board as a result (buzzing through the speaker at all times when powered on even if all parts are working correctly). A heat sink is needed for the speaker drivers, but not the noise overall, thus, just connect a common lead to it the companies say... It's a design thing.

to get an idea (if you don't know) of a transistors speed, the tone of a speaker requires a 2 way motion to produce a tone, fast operation. so the music is the speed of them operating push and pull for the drivers as example, just think drum soloist beating the drum fast enough to produce a solid tone, not a realistic ability, but the metaphor stands.

Awesome!!!!

I wondered about the thermal mgmt. On the soldered side of the board there are those 4 metal bases basically connected to the large white resistors.
Under the metal bases was this white greasy stuff, and some thin plastic sheets between them and the heat sync. Obviously you're in the know about
that.. I supposed I'd need to get some of that material as well, yes?

If this gets operational, it'll be the one gift I get for Christmas (since I have no job yet).. Been out of work since Sept 21 (yikes)!
I'm all about paying it forward however. I wonder what I could do to re-pay you for all your help?

Thanks!

 

[GromTag]

The white grease and plates are important, the plates can be lightly greased with a small dab on the plate, then stuck to the transistor with the hole aligned, then the grease lightly applied to either the sink area where the transistor seats. or on the back side of the plate, (mica, Very soft substance with highest heat transfer commonly found in many amps, Capton, harder thicker and slightly less heat transfer, alto once cheap in comparison to Mica, the once abundant use of Capton has resulted in hard to find surprisingly due to its demand for a period years ago, now its not so easy to find, at least in good quality of material. Mica is no exception to quality issues either. Both are termed Heat insulation. Rather they allow heat energy to transfer but not electricity to the point of a short. those plates, if they are not torn or have any holes in them other than where the screw goes and still can cover the exposed metal on the back of the metal on the transistors can be reused.

Photos, all be it a bit shaky. I'm still developing that third hand from my head holding the phone all ways pulling pranks on me tho...hmm

 

[GromTag]

If you have to, solder a lead from one of those corroded resistors, using a clean lead from one resistor from the parts side to the solder side. to help hold the track down to clean off the coating.
Then the light scraping will have less effect on possibly lifting any more track.

 

[chinjazz]

If you have to, solder a lead from one of those corroded resistors, using a clean lead from one resistor from the parts side to the solder side. to help hold the track down to clean off the coating.
Then the light scraping will have less effect on possibly lifting any more track.

Yes, this is what I was thinking on an as needed basis.

 

[chinjazz]

Think these are still good? One is broken, but the pressure under the screw could keep it together...

 

[chinjazz]

One other question before I place orders...
Connector wire that was fabbed for the non GND loopy thing was made with Radio Shack connector wire (copper). This adequate or some other wire is better? My first go at it seemed that it didn't hold really snug. I pre-tinned them but I wasn't completely happy with it.

 

[GromTag]

Those are plastic, or a very thin Mica plate, the stress marks indicate thin mica. and no, I would not advise the reuse of them. because those stress points can brake during snugging of the screw on assembly and allow potential a short even with non conductive grease, as the transistors heat up, that grease becomes malleable (soft like a fluid gel -pliable) and can ooze away allowing a metal to metal contact short. And the broken one, did it come off like that? or was it stressed then broke rather easily after removal?

As for the wire used, that will be ok, as it only enables the field produced by the board in operation to be absorbed so to speak to a close by return point. That large block of aluminum would act as an overgrown antenna, holding a low charge, especially from being any where near that speakers magnet, and the pcb being so close, this field would play havoc on near by components that were sensitive to it. Transistors primarily in general have an amazingly low static transfer rate, until energized or connected in a shielded manner. The manufacturers method is just to use a gnd plane for return. As long as the leads reach, and able to be installed, and are not too long, as this could bunch up between the board and sink, it will work fine. As for tinning the ring leads, would help to increase the transfer, tho not really needed. As for tinning to help then hold together better, that would help, however I have not seen if those leads (Oring) would be kept away from the other contacts on the power pcb when everything is assembled together.

 

[chinjazz]

Those are plastic, or a very thin Mica plate, the stress marks indicate thin mica. and no, I would not advise the reuse of them. because those stress points can brake during snugging of the screw on assembly and allow potential a short even with non conductive grease, as the transistors heat up, that grease becomes malleable (soft like a fluid gel -pliable) and can ooze away allowing a metal to metal contact short. And the broken one, did it come off like that? or was it stressed then broke rather easily after removal?

Actually I was having difficulty after removing the screw getting it to lift off the aluminum heat sync, and I broke it on lift.
I'll look for replacement Mica plate material..

As for the wire used, that will be ok, as it only enables the field produced by the board in operation to be absorbed so to speak to a close by return point. That large block of aluminum would act as an overgrown antenna, holding a low charge, especially from being any where near that speakers magnet, and the pcb being so close, this field would play havoc on near by components that were sensitive to it. Transistors primarily in general have an amazingly low static transfer rate, until energized or connected in a shielded manner. The manufacturers method is just to use a gnd plane for return. As long as the leads reach, and able to be installed, and are not too long, as this could bunch up between the board and sink, it will work fine. As for tinning the ring leads, would help to increase the transfer, tho not really needed. As for tinning to help then hold together better, that would help, however I have not seen if those leads (Oring) would be kept away from the other contacts on the power pcb when everything is assembled together.

This deal was something I made, a replacement to something that was the same two leads connected to one O-ring (brass), but it was un-usable because
aside from the wires being connected, there was an extremely hard substance - perhaps epoxy or the like that coated on top of that.
So I made two and they screw together on top of each other to the aluminum sync. They don't touch anything else basically.

I think it's ok based on what it was before.

 

[chinjazz]

I guess Mica heat insulation won't be too hard to find: https://www.walmart.com/ip/200-Pcs-...8760&wl11=online&wl12=151329551&wl13=&veh=sem

 

[GromTag]

Mica, possible pieces, as for their thickness, those from that amp are thin, good heat transfer, the ones here https://www.digikey.com/product-detail/en/4672/36-4672-ND/27401?WT
These may be thicker, less heat transfer, the datasheet spec states the small holes at lower are for the transistors pins, in your case those can be left as is, if they are large enough to be correct, or trim those 3 small ports off. High temp tho by said datasheet. 1100 deg F. An .003 to .001 thickness. means they vary in thickness. this is not a realistic problem really, as I doubt you'll try to run them in a Class D 1000Watt and above heat range resulting in thermal off Bias..

 

[GromTag]

that wallmart appears to be (all tho I can not for some reason see the images on that site) for Microwave ovens, the Magnetrons antenna cover plate, allows the frequency through, but helps to reduce some temperature (minor) and signal latching back to the Magnetron resulting in a quite impressive boom (major). note some 900W microwaves can be close to 20,000 Volts and higher (not so much current tho) only be referring to the capacitor for the transformers phase usually at the do not exceed 22,000 V. :EDIT: just a fun factor add in about things that could be unexpectedly dangerous in the household:

 

[GromTag]

And yes that is a poor made cheap capacitor, just stating that for any that may chime in about its country of origin.

 

[chinjazz]

Mica, possible pieces, as for their thickness, those from that amp are thin, good heat transfer, the ones here https://www.digikey.com/product-detail/en/4672/36-4672-ND/27401?WT
These may be thicker, less heat transfer, the datasheet spec states the small holes at lower are for the transistors pins, in your case those can be left as is, if they are large enough to be correct, or trim those 3 small ports off. High temp tho by said datasheet. 1100 deg F. An .003 to .001 thickness. means they vary in thickness. this is not a realistic problem really, as I doubt you'll try to run them in a Class D 1000Watt and above heat range resulting in thermal off Bias..

Perfect! And since I'm already ordering from digikey.

 

[chinjazz]

that wallmart appears to be (all tho I can not for some reason see the images on that site) for Microwave ovens, the Magnetrons antenna cover plate, allows the frequency through, but helps to reduce some temperature (minor) and signal latching back to the Magnetron resulting in a quite impressive boom (major). note some 900W microwaves can be close to 20,000 Volts and higher (not so much current tho) only be referring to the capacitor for the transformers phase usually at the do not exceed 22,000 V.

Glad your helping me not get the wrong stuff!

Thanks much!

 

[GromTag]

those Keystone do fit a variety of transistors, however, no data yet exist that I have oh those 4 Transistors on the sides of the power pcb. here is the spec for the size of the plates themselves in measurement term. Measurements are usually in millimeter, but the datasheet seems to state p inch thickness terms, over viewing this datasheet.

these have indicated for 220 case, that would be those smaller transistors in between the needed larger transistors.

 

[GromTag]

the section containing thermal pads from Digi, And am looking at the photo for a closer case style on those larger transistors also. they look TIP size ranged
https://www.digikey.com/product-search/en/fans-thermal-management/thermal-pads-sheets/1179751