I've got this amp that had burned supply fets. I've replaced them but if I power up the amp it immediately draws >20Amps. So I disconnected the output of the transformer from the amp board, and the current draw dropped to less than an amp and I get 120VAC across the output of the transformer.
So, with power connected, if I attach either output from the transformer to the PCB current draw jumps again.
I've checked the output transistors, and they all seem Ok. No shorts, and diode check passes on them. I've checked the rectifiers and they are Ok. I don't have anything hooked up to the rca inputs or to the speaker outputs. What should I check next?
Thanks!
KyferEz
So, with power connected, if I attach either output from the transformer to the PCB current draw jumps again.
I've checked the output transistors, and they all seem Ok. No shorts, and diode check passes on them. I've checked the rectifiers and they are Ok. I don't have anything hooked up to the rca inputs or to the speaker outputs. What should I check next?
Thanks!
KyferEz
Clamp the transistors to the sink to prevent damaging them while troubleshooting.
Have you checked all of the gate resistors for the power supply FETs?
Have you tried turning the bias control down to see if the current draw dropped to normal?
If that doesn't work, measure the voltage across each of the emitter resistors while the amp is powered up. With the bias set low, there should be essentially no voltage across any of the emitter resistors. If you find one or a group that have more than ~0.001v (with the bias set to the minimum position), it will help you determine where the fault is. If you have a large 2 ohm resistor, insert it in the B+ line to help prevent damage to the amp while troubleshooting.
Most of the ZR1000s I've seen had no fuse in the RCA shield circuit but a few were modified. To confirm that the shield ground is intact, measure the resistance from the input RCA shield to the transformer's secondary center tap. It should be ~0 ohms.
Have you checked all of the gate resistors for the power supply FETs?
Have you tried turning the bias control down to see if the current draw dropped to normal?
If that doesn't work, measure the voltage across each of the emitter resistors while the amp is powered up. With the bias set low, there should be essentially no voltage across any of the emitter resistors. If you find one or a group that have more than ~0.001v (with the bias set to the minimum position), it will help you determine where the fault is. If you have a large 2 ohm resistor, insert it in the B+ line to help prevent damage to the amp while troubleshooting.
Most of the ZR1000s I've seen had no fuse in the RCA shield circuit but a few were modified. To confirm that the shield ground is intact, measure the resistance from the input RCA shield to the transformer's secondary center tap. It should be ~0 ohms.
Gate resistors for the FETs are fine.
I'm not sure what you mean by setting the bias low. I do see some pots in the amp circuitry, but don't know which way to turn them to set the bias low? How do I figure this out?
In any event, I tested all of the emitter resistors with the amp powered up and the transformer secondary reconnected. None of them had any voltage across them.
This ZR1000 does have the fuse. Connection from shield to center tap is good.
Thanks!
KyferEz
I'm not sure what you mean by setting the bias low. I do see some pots in the amp circuitry, but don't know which way to turn them to set the bias low? How do I figure this out?
In any event, I tested all of the emitter resistors with the amp powered up and the transformer secondary reconnected. None of them had any voltage across them.
This ZR1000 does have the fuse. Connection from shield to center tap is good.
Thanks!
KyferEz
sorry to threadjack a bit....
Perry,
I bought a broken ZX1000.1 amp and it has all PS fets burned, output fets seem OK, all drivers don't seem to be burned. what started it seemed to be the output inductor which is black and really toast. I was wondering what is the inductance value of this as I intend to replace it with an MPP core of the same size as I think the heat could have permanently changed the core characteristics and have some MPP cores coming my way. also, will this amp be safe to test run without a sink?
Perry,
I bought a broken ZX1000.1 amp and it has all PS fets burned, output fets seem OK, all drivers don't seem to be burned. what started it seemed to be the output inductor which is black and really toast. I was wondering what is the inductance value of this as I intend to replace it with an MPP core of the same size as I think the heat could have permanently changed the core characteristics and have some MPP cores coming my way. also, will this amp be safe to test run without a sink?
I've got good news and bad news.
The bad news is that while I was testing the amp, something in the audio section went pfffzzit and I smelled the magic smoke. The high current pull dropped down to less than an amp, and then started ramping up. Now the protect light comes on and the outputs get hot over the course of a minute or two.
The good news is that the supply now outputs a good +55V after the rectifiers! So whatever was causing the short seems like what fried.
So I've got no idea what burnt. I do know the general area of the part that burnt... What now? Test all of the smaller transistors?
The bad news is that while I was testing the amp, something in the audio section went pfffzzit and I smelled the magic smoke. The high current pull dropped down to less than an amp, and then started ramping up. Now the protect light comes on and the outputs get hot over the course of a minute or two.
The good news is that the supply now outputs a good +55V after the rectifiers! So whatever was causing the short seems like what fried.
So I've got no idea what burnt. I do know the general area of the part that burnt... What now? Test all of the smaller transistors?
I've looked and looked. I can't find anything visibly damaged except for a 36k smt resistor that looks like it has gotten hot, but it's fine.
Edit: could the original problem have been caused by one of the supply's filter caps??? I just noticed one is swelled on the top and I don't think it was before.
Edit: could the original problem have been caused by one of the supply's filter caps??? I just noticed one is swelled on the top and I don't think it was before.
So I don't forget... After you find all of the problems and have replaced all of the defective parts, you should push, pull, twist the winding on both the power transformer and the inductor while monitoring the current draw to make sure that none of the windings are intermmitently shorted. I've see this problem often in the ZR series amps.
Are the outputs in 'both' channels heating up?
If so set the bias pots for minimum idle current from the power supply.
If only one channel is getting hot and the bias pots are set to the minimum, begin your search for defective parts in the channel that's getting hot. Shorted or leaking drivers are the most likely cause for excesive current draw (if the output transistors are not shorted or leaking).
It's possible that the capacitor was shorted and was causing the excessive current draw.
Are the outputs in 'both' channels heating up?
If so set the bias pots for minimum idle current from the power supply.
If only one channel is getting hot and the bias pots are set to the minimum, begin your search for defective parts in the channel that's getting hot. Shorted or leaking drivers are the most likely cause for excesive current draw (if the output transistors are not shorted or leaking).
It's possible that the capacitor was shorted and was causing the excessive current draw.
Only one side is gets hot - the side that didn't have smoke come from it...
I wiggled and pushed and pulled as much as possible on the transformer and inductor (they're gluded down pretty tight) and nothing changed.
The side that had smoke come from it stays cool.
I found schematics for the amp here: http://www.schematicsforfree.com/ar...oducts/audio/Kicker_ZR1000_Service_Manual.pdf
I wiggled and pushed and pulled as much as possible on the transformer and inductor (they're gluded down pretty tight) and nothing changed.
The side that had smoke come from it stays cool.
I found schematics for the amp here: http://www.schematicsforfree.com/ar...oducts/audio/Kicker_ZR1000_Service_Manual.pdf
Q211 looks to be leaking; it fails diode tests. It's on the same side that gets hot. It's a CENW42. The ones on the board have little metal heatsinks on the top of them (TO237). The replacements I found don't, they are standard T092 packages. I guess that would increase thermal impedance to air, but I can't find any datasheets for the old parts that list thermal impedance to know if it will matter. What would you use?
U104, a programmable voltage reference, is missing on the side that doesn't get hot. I noticed that last night but forgot to mention it.
U104, a programmable voltage reference, is missing on the side that doesn't get hot. I noticed that last night but forgot to mention it.
What was the original part number (refer to other side if you don't know)?
These are the transistors I've seen in all of the ZR1000s I've worked on.
http://bcae1.com/temp/P7230015b.gif
If you need a 1 watt transistor, use an MPSW42.
I would avoid Central Semiconductor parts. In EVERY blown amp that I've worked on that used Central parts, at least one of the Central parts was defective.
The voltage reference is part of the constant current source. It will have to be replaced before you can do any troubleshooting in the other channel.
These are the transistors I've seen in all of the ZR1000s I've worked on.
http://bcae1.com/temp/P7230015b.gif
If you need a 1 watt transistor, use an MPSW42.
I would avoid Central Semiconductor parts. In EVERY blown amp that I've worked on that used Central parts, at least one of the Central parts was defective.
The voltage reference is part of the constant current source. It will have to be replaced before you can do any troubleshooting in the other channel.
Good to know about the Central parts. I'll order a bunch of MPSW42 and MPSW92 and remove all of the Central parts.
The original PN for U104 is TL431C from Texas Instruments. Do they go bad very often? How can you tell if it is bad? I ask because to try and get this thing working quickly I may snag one from another broken amp I've got laying here.
Thanks Perry!
The original PN for U104 is TL431C from Texas Instruments. Do they go bad very often? How can you tell if it is bad? I ask because to try and get this thing working quickly I may snag one from another broken amp I've got laying here.
Thanks Perry!
The TL431s rarely fail. The IC works to produce a 2.5v difference in voltage between the anode and the reference pins. If you find 2.50v between those two points, the IC is likely OK.
The CENW42s are rated for 2.5w. If the MPSW42s run hot (too hot to touch for more than a few seconds), use a clip-on heatsink to help keep them cool.
Mouser heatsinks (check for vertical clearance if you order the taller one):
532-322400B00
532-575200B00
Also order a few #6-32 NYLON screws if the secondary center-tap pad on the circuit board is not isolated from the board mounting screw. If you use a metal screw and there is no isolation, you will get engine noise if the case/heatsink of the amp contacts chassis ground in the vehicle. Also be sure to replace the plastic support tube under the board so the mounting boss can't contact the board.
The CENW42s are rated for 2.5w. If the MPSW42s run hot (too hot to touch for more than a few seconds), use a clip-on heatsink to help keep them cool.
Mouser heatsinks (check for vertical clearance if you order the taller one):
532-322400B00
532-575200B00
Also order a few #6-32 NYLON screws if the secondary center-tap pad on the circuit board is not isolated from the board mounting screw. If you use a metal screw and there is no isolation, you will get engine noise if the case/heatsink of the amp contacts chassis ground in the vehicle. Also be sure to replace the plastic support tube under the board so the mounting boss can't contact the board.
Thought I was making headway... Nope. I added the TL431 and that side of the amp very quickly blew the output transistor (I only had 1 output transistor on each side of the amp). So... I really don't know what to look at. All of the transistors I check appear Ok, at least using the diode check. Some were suspect and I removed them and they test Ok. Some have that shiny area on the bottom around the legs like sometimes when the fry, but the one I pulled didn't have any shorts and passed diode test. The one I didn't pull has no shorts. These are the MJE15030 and 15031s
I'm stuck.
I'm stuck.
You need to use a current limiter. The most common limiter is a 2 ohm resistor (50 watts or larger). Some people use a headlamp (H6054, both filaments in parallel). These go in the B+ line.
If you don't have a resistor or headlamp, use a relatively small fuse (~10 amps) in the B+ line.
Having the power transistors tightly clamped to the sink will help prevent blowing them.
The first thing you need to do is to determine the minimum bias position. It's most likely fully counter-clockwise but in some amps, fully clockwise is the minimum position. One amp had one of each. That was a bit confusing. To determine the minimum positon, monitor the voltage with the voltmeter across the emitter resistor (at a location where a transistor is installed). With the bias set to the minimum, the transistors won't run hot unless there is a defect.
With the bias set to the minimum position, do the outputs in either channel run hot?
Is there DC on either channel? Measure the voltage on the emitter resistors if the relays are not engaging.
You should work on one channel until you get it working, then move to the other channel.
If you don't have a resistor or headlamp, use a relatively small fuse (~10 amps) in the B+ line.
Having the power transistors tightly clamped to the sink will help prevent blowing them.
The first thing you need to do is to determine the minimum bias position. It's most likely fully counter-clockwise but in some amps, fully clockwise is the minimum position. One amp had one of each. That was a bit confusing. To determine the minimum positon, monitor the voltage with the voltmeter across the emitter resistor (at a location where a transistor is installed). With the bias set to the minimum, the transistors won't run hot unless there is a defect.
With the bias set to the minimum position, do the outputs in either channel run hot?
Is there DC on either channel? Measure the voltage on the emitter resistors if the relays are not engaging.
You should work on one channel until you get it working, then move to the other channel.
I just didn't expect the current surge simply from installing the TL431... I'll use my load box at the +b input from now on. I like to leave the amp out of the case because it allows me to tell what components are getting hot much easier. Yes I risk higher chances of frying them. It's a chance I'm willing to take.Perry Babin said:
Found it. Transistors still were getting hot and there was DC over a volt DC on one channel. The other channel has no outputs on it yet. While checking voltage across the resistors, one of the MJE15031s blew for no discernible reason. It's turned out to be a good thing! I replaced it with the one I had removed (to test) from the other channel and now this channel no longer gets hot! I think this channel is fixed!
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