JBL scs175 subwoofer amp fried need help to fix it!

[marlongtt]

Hi there fellows,
nice way to start a post in this community after a while i've been reading you.

Today i put my hands on a brand new USED HT kit from jbl.
I got it by a guy not near my door, so i make a shipment.

When i got it from the courrier, i find out, two satellite's cone with the frame slightly broken (it is in palstic!!!).
This is a mechanical issue, and i can explain that, a bad box has been made for that shipment.

What what sounds strange, is the subwoofer, that came with few scuff, simply did not work.

i take the amp apart, and i find that some tracks on the pcb was overheated.
That was related to a unknown C20 capacitor blown up.
I then fixed the tracks with some wire as you can see.

**broken link removed**
**broken link removed**
**broken link removed**

Then i bought a capacitor with the same size of on near him , the C19 (on the right in the picture) which is written 221 on it.

The resistor that you see blown up, was still not blowed.
I measured it, and it was 0.56 on the 2k scale on my tester.

I measured it while it was on board (i did not take it apart)
I wasn't able to understand the color, they really seems green-blue-black, but i cant really say what is the last color.

Back to the shop, i installed the new capacitor.
Closed up everything, and it was running fine.

Listen to the sub for a while , then it stop playing music, and it began with a continuous buzz, even at low to mute volume. A bad smell came out from the sub.

Itake it apart and realized that the resistor i was telling before, was now blewn up.

The capacitor was still there in good shape.


now, i need some help.

I am not able to find the service manual for this sub.

I find the link on this site of this, wich has pretty the same specs, but it is different (still 100w HT sub dunno if 4 or 8 ohm mine is 4)

**broken link removed**

then i find the manual to be paid here

JBL - SCS 175 Sub Service Manual on Windows Drivers Downloads

but it cost around 10 usd.


Do you think i am gonna find the right manual there?

Or do you amp gurus are able to help me someway to find an alternative resistance and confirm that it may be the right capacitor the one i put it in.

The main problem may be the wattage of that resistance.
it is soo big compared to the 2w....


the day after i bought the SM

i pay the money down, and then i got the schematics.

Now i changed the huge (in dimensions) 56ohm 1 watt that was fried, and replaced with a normal size same specs one.

when i plug the power back and switched on (witout no input neither speaker connected) it immediatly fried out again.

What now?

here is the schamatic:
scs175_preliminary_sm.pdf - File Shared from Box.net - Free Online File Storage

the restitor i am talking about is R44, the capacitor i have replaced (now i know it is correct value the one i put into)
is C20.

i really suspect, that since this component are really near the transistor Q11 whch is a C3421 it may be damaged itself and causing the resistance to burn out.

TR datasheet is here

**broken link removed**

Now a buzz sound come out from the speker at every volume ,and without no input connected.

please help me.

 

[rfs100]

Ok

Simply replacing burned out components seldom repairs a circuit. Without testing skills all you are doing is simply recreating the fault, and probibly doing even more damage. I doubt that the manual that you are considering purchasing will be of any help in troubleshooting or repair, whatsoever, so save your money, and take it to a repair shop, or return it to then chap you bought it from , as obviously this problem existed prior to being shipped, and has nothing to do with shipping damage.

 

[marlongtt]

lease see this post for the definitive results:

Q10 2sc3421 npn:
B-C: 1.119 kohm
B-E: 1.127
E-B=C-B=OPEN CIRCUIT
C-E=E-C=OPEN CIRCUIT

Q11 2sc3421 npn:
B-C: 1.094 kohm
B-E: 1.100
E-B=C-B=OPEN CIRCUIT
C-E=E-C=OPEN CIRCUIT

Q12 2sA1358 pnp:
B-C: 1.068 kohm
B-E: 1.075
E-B=C-B=OPEN CIRCUIT
C-E=E-C=OPEN CIRCUIT

Q13 2sd718 npn:
B-C: 0.011 kohm
B-E: 0.011 kohm
E-B=C-B=0.011 kohm
C-E=E-C=shortCIRCUIT

Q14 2sb688 pnp:
B-C: short
B-E: open
E-B=open
C-B=short
C-E=E-C=open


now what??

 

[rfs100]

Good work man...hell you could replace all these semis for under 10.00

 

[krytenrobot]

This is a class b push-pull amplifier, i would replace the transistors Q13 and Q14 as they have blown,i would replace the resistors as well (r44 56ohm 1w, r45 r46 both 0.22 ohms 3w) the voltage at the speaker terminal should be half of the supply of +vcc/-vcc, if its not its due to r39 and Q11.

 

[marlongtt]

I tested the protection circuit ONBOARD:

R51=R52=spec value (5,6kohm)
R50=5,55 (spec value 5,6) out of tolerance 5%
R53= 9,8kohm (spec value 10k) in tolerance 5%

Q02 (2sa1015 pnp) in board seems ok,
Q03 (2sa1015) seems ok too.

diodes, ok.
There are differences between diagram and real world:

components R 48, 49, 54 and ZD03 are missing on the pcb.




I tried to test the main +- rail too ( i hope i did it right):
I checked and find that:
from B(q13) to B'(q14) there is the r44 value (as per diagram)
from E to E' there is R45+R46.

From C to C' tester showed an increasing value that after few millisecon goes up to open circuit. Is this due to capacitors?

I am not sure i am doing the +- checkup properly, here is a new picture

**broken link removed**


After this checkup I received the componets q13 and q14, and put them on the pcb,, check short and else and installed.

Plug the power and the signal, set the volume low, and switch on.
Raised up the volume, and, everything was running.

i play some music, try different cutoff frequency and volume.

The heatsink took some minutes to warm up,

THEN..... after about 10 min playing, the same happened.

Continuous buzz and component fried smell. PLUS the MAIN fuse on the 220v power burnt.

Take everything apart and the two main trannies were gone again.

But how it is possible this is a time dependant issue?
Can a trannie do such a thing if not properly cooled?
I'm asking this because it is really strange, this time dependency and also , the fact the heatsink is so slow to warm up, when the trannie itself took a second to go hot.

I bought an extra kit of this two components, but now i have only one left, i would like to fix this issue but i am loosing fatih...

please guys help!

 

[audioguru]

When JBL was American they produced excellent products.
But now the Japanese own them and many other good American audio companies and the products are made very cheaply.

 

[marlongtt]

Here is a video documenting the test with dim bulb tester.
please comment

 

[ben7]

Hi there fellows,
nice way to start a post in this community after a while i've been reading you.

Today i put my hands on a brand new USED HT kit from jbl.
I got it by a guy not near my door, so i make a shipment.

When i got it from the courrier, i find out, two satellite's cone with the frame slightly broken (it is in palstic!!!).
This is a mechanical issue, and i can explain that, a bad box has been made for that shipment.

What what sounds strange, is the subwoofer, that came with few scuff, simply did not work.

i take the amp apart, and i find that some tracks on the pcb was overheated.
That was related to a unknown C20 capacitor blown up.
I then fixed the tracks with some wire as you can see.

**broken link removed**
**broken link removed**
**broken link removed**

Then i bought a capacitor with the same size of on near him , the C19 (on the right in the picture) which is written 221 on it.

The resistor that you see blown up, was still not blowed.
I measured it, and it was 0.56 on the 2k scale on my tester.

I measured it while it was on board (i did not take it apart)
I wasn't able to understand the color, they really seems green-blue-black, but i cant really say what is the last color.

Back to the shop, i installed the new capacitor.
Closed up everything, and it was running fine.

Listen to the sub for a while , then it stop playing music, and it began with a continuous buzz, even at low to mute volume. A bad smell came out from the sub.

Itake it apart and realized that the resistor i was telling before, was now blewn up.

The capacitor was still there in good shape.


now, i need some help.

I am not able to find the service manual for this sub.

I find the link on this site of this, wich has pretty the same specs, but it is different (still 100w HT sub dunno if 4 or 8 ohm mine is 4)

**broken link removed**

then i find the manual to be paid here

JBL - SCS 175 Sub Service Manual on Windows Drivers Downloads

but it cost around 10 usd.


Do you think i am gonna find the right manual there?

Or do you amp gurus are able to help me someway to find an alternative resistance and confirm that it may be the right capacitor the one i put it in.

The main problem may be the wattage of that resistance.
it is soo big compared to the 2w....


the day after i bought the SM

i pay the money down, and then i got the schematics.

Now i changed the huge (in dimensions) 56ohm 1 watt that was fried, and replaced with a normal size same specs one.

when i plug the power back and switched on (witout no input neither speaker connected) it immediatly fried out again.

What now?

here is the schamatic:
scs175_preliminary_sm.pdf - File Shared from Box.net - Free Online File Storage

the restitor i am talking about is R44, the capacitor i have replaced (now i know it is correct value the one i put into)
is C20.

i really suspect, that since this component are really near the transistor Q11 whch is a C3421 it may be damaged itself and causing the resistance to burn out.

TR datasheet is here

**broken link removed**

Now a buzz sound come out from the speker at every volume ,and without no input connected.

please help me.

Hmm, the burnt area is around where the high power resistor was ,ceramic cap, and near a diode too.
Perhaps this is a zener diode that has burned out, giving part of the amp too much voltage, then frying it!

Also, is the resistor that you took out properly put back in it's place?

 

[Chippie]

the voltage at the speaker terminal should be half of the supply of +vcc/-vcc, if its not its due to r39 and Q11.

Sorry you are wrong...There should be no dc voltage at the mod point wrt to Ov...