M&K Subwoofer Amp Fault, Help Anyone?

[GES1407]

Hi Guys,

I have bought a M&K subwoofer as faulty in the hope of repairing it, i cant find the model number because it has been removed, but the amp board inside is identical to a picture of an MX-100 board from M&K, the sub was working & suddenly stop outputting & only made popping & rumbling noises, the amp was powered & led lit, also no sound is heard now when you connect an rca lead, but was before, i opened it to inspect the board & someone had already carried out a repair(badly!) the board had heat patches, tracks lifted, capacitors of wrong value leaking, & a few capacitors with only 1 leg connected! how it worked i dont know! anyway i cant find schematics for this to try to repair any further or have a new board made up, so any help would be appreciated! i have attatched a pic of the board, i have had to remote a few components as the tracks underneath wouldnt take the solder properly, & kept unsoldering other bits around it, so looks a mess, Oh & the 12" dual voice coil driver thats installed (2x6ohms) still works fine, personally i think its an input prob, but just incase have a new STK4050v on order. Thanks.

[h3ad]

hmm well by the looks of the pic it was repaired by a 10 yr old, but if u cant find scematics i would trace the main input of the power amp, and just use your own active crossover network, like find the point where the crossover/preamp inside the unit joins to the main amp and join an input to that, or it might be easier just to install a new amplifier.
another problem is that because the preamp might b dead (as an assumption) and it is a DVC woofer it uses 2 amps, so you might need to find 2 inputs, but if it is the main amplifier you might just have to replace the output transistors, and MAYBE a few resistors.

what is the ratings of the amplifier and subwoofer?? and i have never heared of a dual 6R woofer before, what brand is it?

haydn

[h3ad]

ahh i just realised after posting that message that the power amp is a power IC, here is a sight that u can purchase a new chip if needed http://www.ampslab.com/trans_stk4050v.htm

haydn

[GES1407]

Hi, thanks for your help, i have found 2 zener diodes burnt out on the board, so replaced them with like for like & still no joy, just a voltage sound when i power up the amplifier, i have ordered a new stk4050v & it arrived this morning, so im hoping that the bad solder job had shorted out & blown the amp, so if i replace this it should work, also found 2 tracts that were broken so have repaired them, so it all relies on whether installing this new amp chip cures it, otherwise i think i've exhausted every option & will just bin it.

[GES1407]

oh and its branded M&K, its 200w per coil from what i can find out, at 6 ohms per coil, bit of an odd impeadance but most of the time if its labelled 8 ohms it drops under certain loads or frequencies, so i base the driver on a 4 ohm load while under load, hope i can get this fixed, the bass was awesome & so deep before when it worked, its just a shame to not have it working properly.

[GES1407]

Just finished with the amp, fitted new stk chip & new lm348 op-amps, repaired all broken track hiden under where the stk chip was & thoroughly checked everything on the board and...............Still nothing, so i gave up now & the board is in a million pieces lol. removed the 110 transformer & output capacitors from the sub box, they work fine so will keep them like all the other junk i got, just gonna buy a new plate amp, found prices around $100 so about £50 in my money, so not too expensive. Thanks for your help guys, shame the board was beyond repair but you have to give up sometime!

P.S got a stk4050v chip if anyone needs one! lol (can have for what i paid) & 2 10,000 mf at 63volt so gimme a shout if anyone needs them.

[h3ad]

ill take the old board off your hands if thats ok, with he chip and so on, the caps & transformer i probly have, so yeah how much??
also do you still have the old amp chip?? and the op amps? becaus eif u do chuck them in if thats ok

thanx haydn

[GES1407]

Originally posted by h3ad
ill take the old board off your hands if thats ok, with he chip and so on, the caps & transformer i probly have, so yeah how much??
also do you still have the old amp chip?? and the op amps? becaus eif u do chuck them in if thats ok

thanx haydn

the boards in bits mate, i had enough of it, i still have the new stk chip, the old one had some pins not connected & didnt meter out properly so binned it too, so all i have is the stk chip, cappys, transformer & the new lm348 op amps, the old op amps were fine so gonna hang on to them, would be looking for £10 plus postage to get my money back (paid £12 for the amp alone) let me know if u interested. The STK chip has been soldered onto the board & removed again so might need the pins cleaning up.

[h3ad]

i am interested and to be fair i will give u 15pounds for it + postage. if u r thinkin of sending the transformer, because i am unsure if u are, dont worry about it, keep it as Australia uses 240v and it will just make sum pretty smoke over here. i would assume postage would be aroun the 5pound mark?? so call it $50- $55 AUD??

thanx haydn

[h3ad]

also if possible could u inclide the board? even if it is stripped it doesnt matter, i am a diy-aholic i can help myselp but fiddle n fix things, or build things lol

thanx haydn