JBL Crown BPX1100.1 problems

[shagone]

I'm working on a JBL Crown BPX1100.1 amp that looks like it had reverse voltage applied to it. the input terminal has marks on it from arcing. all of the irf3205 power supply fets were fried along with all of the outputs from one side of the amp. i replaced all of the p/s fets and bad outputs and i checked the drive transistors and they seem to check ok for the p/s and outputs. now when i hook up power and ground only i get no high current but when i apply remote voltage the blue protect light flashes and the ammeter on my bench supply spikes on and off and it even causes my test head unit to cut on and of. the user maunal for the amp sais that a flashing protect light means that there is a short circuit in ther speaker wires. i had no signal going into the amp and no speakers hooked up during this initial test.

i guess i'll look closer at the output side of the board for shorts but i was hoping someone here might be able to give some suggestions or lead me in the right direction.

Also, does anyone have a service manual handy for this amp?

[Perry Babin]

Email me for the manual.

It didn't fail from reverse polarity. Reverse polarity would not have damaged the outputs.

It probably has defective driver transistors. If you tell me which outputs failed, I can tell you which components to check.

[jol50]

Sometime that is from the terminal not being tight, or getting dirt/corrosion/moisture in it, etc. I've seen a few amps that way.

[shagone]

Originally posted by jol50
Sometime that is from the terminal not being tight, or getting dirt/corrosion/moisture in it, etc. I've seen a few amps that way.

was that on JBL amps? is the protection circuit that sensetive?

i think i found some bad drivers but i'll work on it more tommorow.

[Perry Babin]

Look for 1 ohm resistors connected to the driver transistors (may be on the bottom of the board). Check each one after removing the defective driver transistors. Many times they open.

Also look for defective 12v Zener diodes. If you don't find any that appear to be defective, measure the DC voltage after the amp is powered up to make sure each one has ~12v across it. Sometimes they leak and the voltage is significantly lower than normal. This can cause the outputs to run hot and fail.

[jol50]

Originally posted by shagone



was that on JBL amps? is the protection circuit that sensetive?

i think i found some bad drivers but i'll work on it more tomorrow.

Don't think I have seen a JBL. All brands mid and cheaper, just see them...care could be a factor. Some the plastic under the terminal was melted a little, some had some moisture or something spilled on them, others just had a bad connection and got hot/burnt a little. Have seen it inside the lug type also, and the plastic cover on lugs melted like in Perry's site or CD shows.

[shagone]

Originally posted by Perry Babin
Look for 1 ohm resistors connected to the driver transistors (may be on the bottom of the board). Check each one after removing the defective driver transistors. Many times they open.

Also look for defective 12v Zener diodes. If you don't find any that appear to be defective, measure the DC voltage after the amp is powered up to make sure each one has ~12v across it. Sometimes they leak and the voltage is significantly lower than normal. This can cause the outputs to run hot and fail.

ok, i'll check the 1 ohm resistors.

how do i identify the 12v zeners? are they the small orange and yellow striped ones or do they have markings? what area should they be in?

Thanks in advance Perry. i really want to get this one fixed.

[Perry Babin]

D201, D202, D401, D402 are all 12v Zeners. The part number in the manual is 1N5242 so it should be a standard 1/2w Zener (probably orange). They are very near the drivers.

[shagone]

none of the diodes seem to be open or shorted and all of the 1 ohm resistors seem to check fine. the drivers seem ok too but could be leaky i guess?

when i power the amp up through my 2ohm current limiting resistor the blue light is steady and the ammeter on my supply stays around 5 amps. after less that a minute if i remove power there is one power supply fet that is very hot and everything else is still cold. could this be the problem? it does not read shorted in the board but i guess it could be leaking. should i change it out? i do have a few irf3205's left.

[Perry Babin]

Is the gate resistor for the hot transistor within tolerance?

If you measure the resistance between the gate leg of the hot transistor to the gate leg of a parallel transistor, do you read 2x the gate resistor value?

If the answer is yes to both of those questions, you can try changing out the transistor. The most likely reason it's getting hotter is that it's turning on a little more quickly than the others.