JBL scs175 subwoofer amp fried need help to fix it!

marcogt

Member
2007-11-06 6:59 pm
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.

PICTURES IF YOU CLIC 1 time and then in the corner bottom left, they became big enough to see every details
[IMGDEAD]http://img819.imageshack.us/img819/1696/001fy.jpg[/IMGDEAD]
[IMGDEAD]http://img838.imageshack.us/img838/4801/002jl.jpg[/IMGDEAD]

Uploaded with ImageShack.us
[IMGDEAD]http://img202.imageshack.us/img202/663/003eh.jpg[/IMGDEAD]

Uploaded with ImageShack.us

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)

http://manuals.harman.com/JBL/HOM/Service Manual/TLXPS10 sm.pdf

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....


please help!!!
 
Last edited:

marcogt

Member
2007-11-06 6:59 pm
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.

Now a buzz sound come out from the speker at every volume ,and without no input connected.
 
You really need to check all the transistors Q10, 11, 12, 13 & 14 to make sure they have not blown. If I was servicing this amp I would automatically replace all of them as they may be damaged.
I suspect the amp may have been overloaded at some stage. The subwoofer also needs checking as it could have gone short and caused the damage. Its unlikely the capacitor C20 was the case only part of the symptoms.
 

marcogt

Member
2007-11-06 6:59 pm
bone said:
You really need to check all the transistors Q10, 11, 12, 13 & 14 to make sure they have not blown. If I was servicing this amp I would automatically replace all of them as they may be damaged.
I suspect the amp may have been overloaded at some stage. The subwoofer also needs checking as it could have gone short and caused the damage. Its unlikely the capacitor C20 was the case only part of the symptoms.

hi bone thanks for you help.

The real story of this sub is this.

It was shipped as hardly used, like new.
It was supposed to be more than functional.
When i got it i found it with the feets support broken, and with the heatsink bended due to a bad stroke, made during the shipment. In fact also 2 satellites were damaged.

I tested it on the arrival, and no sound was going out the speaker only a small fuzz and when i switched off, there was like a parasite current that come back in the speaker like it was possesed, afeter few second after the switch was in OFF position.

I then open the amp, and i find out that the PCB was seriously bended, due to the stroke of before.

Then i remove the electronic and straighten the metal frame where the pcb is hooked to.

Then i checked the tracks, and see they was fried a bit, and replaced it.

Then changed the the cap, and it was running.

I took everything togherter again and runninf fine for like 4 minutes. then the continuous buzz at every volume and the fried smell.

R44 was gone, and i changed it but it immediatly blown again.

how can i check if this transitro are messed up???
 

marcogt

Member
2007-11-06 6:59 pm
ok here i am with the first report:

i have tested some transitor, and they seems fine exept from the two main ones.

Q13 and Q14 in, (which are stated to be D1047 and B817 in schematics) are in fact a D718 and a B688.

one is PNP and the other NPN, i have datasheets for both that helped me to find the right pin for base collector and emitter.

Here is what i read with multimeter in DIODE position (2k range):

D718 PNP :has collector and emitter shorted in one way plus base-emitter = base to collector in both way, rated at a value .038 (in 2k range, reallly near short value)

D688 NPN : base to emitter .027 in 2k range,base - collector OPEN CIRCUIT;
THE SAME VALUES in the other way too (no good)


what do you think?
 

marcogt

Member
2007-11-06 6:59 pm
ok here i am with the first report:

i have tested some transitor, and they seems fine exept from the two main ones.

Q13 and Q14 in, (which are stated to be D1047 and B817 in schematics) are in fact a D718 and a B688.

one is PNP and the other NPN, i have datasheets for both that helped me to find the right pin for base collector and emitter.

Here is what i read with multimeter in DIODE position (2k range):

D718 PNP :has collector and emitter shorted in one way plus base-emitter = base to collector in both way, rated at a value .038 (in 2k range, reallly near short value)

D688 NPN : base to emitter .027 in 2k range,base - collector OPEN CIRCUIT;
THE SAME VALUES in the other way too (no good)


what do you think?

please 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??
 
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: This one Defective
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: This one defective
B-C: short
B-E: open
E-B=open
C-B=short
C-E=E-C=open
 

marcogt

Member
2007-11-06 6:59 pm
coolet said:
Q13 2sd718 npn: This one Defective
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: This one defective
B-C: short
B-E: open
E-B=open
C-B=short
C-E=E-C=open

thanks!

should i change the same the whole group of q10-q14 or only defective ones?
do i need to test hFE onn the transistor that are currently working?
if yes i don't know how to do it :eek:

do u want me to test also Q01->Q9?

do i need to test caps?

i found the spare transistors on the -bay i want to order and i want to make a global order.

thnks again.
 
one question... did you test the trannies out of the circuit?

the reason why the resistor burnt is because the power +/-rail goes direct to that resistor due to short in base collector of Q13 & Q14. Now since you are already making a check-up why not check all associated transistor, resistor values. check for short circuit on the PCB track. I see you make some jumpers.
 

marcogt

Member
2007-11-06 6:59 pm
i don't think i get all what you said, sorry for my poor skilled english :eek:

step by step

one question... did you test the trannies out of the circuit

the values i posted about transistors q10- q14 are measured after i removed them from the pcb, is it this what you meant?

check for short circuit on the PCB track. I see you make some jumpers.

what you mean for jumpers? the wire i put where the tracks were burnt?
in that area i carefully check shorts (which i may caused) but everything was ok.
do you want me to check other areas?

the reason why the resistor burnt is because the power +/-rail goes direct to that resistor due to short in base collector of Q13 & Q14

can you explain this like for dummies? :trapper: :p

Now since you are already making a check-up why not check all associated transistor, resistor values.

i can do it, but do you mean checking EVERY single component out of the pcb? this is a huge work....,or i am i misunderstanding what you said?

again thanks.
 
THIS IS RIGHT :D
the values i posted about transistors q10- q14 are measured after i removed them from the pcb, is it this what you meant?



YES THE WIRES. MIGHT BE TOUCHING SOMEWHERE WHEN THE SUBSWOOFER IS IN ACTION DUE TO VIBRATION.
what you mean for jumpers? the wire i put where the tracks were burnt?
in that area i carefully check shorts (which i may caused) but everything was ok.
do you want me to check other areas? JUST DOUBLE CHECK IT.


SEE ATTACH
can you explain this like for dummies? :trapper: :p


LOL!! TROUBLE SHOOTING IS REALLY A HEADACHE ;)
i can do it, but do you mean checking EVERY single component out of the pcb? this is a huge work....,or i am i misunderstanding what you said?


YOU MIGHT CONSIDER TO CHECK THE PROTECTION ENCIRCLED WITH BLUE
 

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marcogt

Member
2007-11-06 6:59 pm
i'm having hard times in my homeworks.....

1. in SECURITY circuit you posted, there are differences between diagram and real world:

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

should i go on to take out the PROTECTION components and test em one by one?
I don't know how test the C22 cap and i don't have a capacimeter.

2. I can't figure out how to check the +- rails. I am not able to identify them on the pcb.
where should i put the tester ends to measure resistance?


below it is 2 new pictures with some detailed added, please download them to zoom in more.

3.The other trans already tested which seems working, should i replace em, should i hfe test em (dont know how) or i don't have to mind bout em?


thanks

[IMGDEAD]http://img52.imageshack.us/img52/2108/p10003881c.jpg[/IMGDEAD]

[IMGDEAD]http://img839.imageshack.us/img839/4773/p1000387f.jpg[/IMGDEAD]
 

marcogt

Member
2007-11-06 6:59 pm
I have a small update:
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.


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?

It should then be ok.

I hope to see coolet around reall soon :p
 

marcogt

Member
2007-11-06 6:59 pm
hi everyboby, today sad day.

I received the componets, 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!
 
the fact the heatsink is so slow to warm up, when the trannie itself took a second to go hot.

Did you use thermal grease to couple the transistors thermally to the heatsink?
Did you use insulating washers to isolate the transistors electrically from the heatsink?

Look up what a Dim Bulb Tester or a Light Bulb Tester is and use it the next time you check the amplifier. Have you measured the impedance of the subwoofer? And the insulation between coil and basket?
 

marcogt

Member
2007-11-06 6:59 pm
hi pacificblue, nice to se you here!

Did you use thermal grease to couple the transistors thermally to the heatsink?

Did you use insulating washers to isolate the transistors electrically from the heatsink?

There is a mica insulator, for the 3 trannies hooked to the heatsink, but NO i do not use grease.
The first time i open everything up, there was a sligtly amount of white stuff (i suppose it is NON conductive grease)

I imagine i cannot use thermal paste for cpu cooling, as it's metal based isn't it?

Screw and washers are the stock one.

Look up what a Dim Bulb Tester or a Light Bulb Tester is and use it the next time you check the amplifier.

Good point! I never heard about it (and you knew that :hohoho:) i will do it , immediatly, can you explain me how to use it??

Have you measured the impedance of the subwoofer? And the insulation between coil and basket?

3,5ohm in the coil, and no i did not check the basket insulation, i will do it today.


today i am receiving also a new multimeter for testing some components. This have CAPACIMETER, would you like me to test some cap?

thanks everybody.