Home |
Search |
Today's Posts |
|
Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
|
|||
|
|||
QSC model 1700 amplifier
Just took in a QSC 1700 stereo power amplifier with a dead channel. This is
a typical large (500W/chan) power amp and some quick checks reveal a bunch of shorted output transistors. Are there any tricks or quirks to this particular amp? Also does anyone know the procedure for adjusting the bias? |
#2
|
|||
|
|||
No real tricks just be sure to change the transistors in pairs. You will
need to remove them to test them. I would also check the driver transistors Q1&2. If you do not have a distortion analyzer you set the bias by monitoring the driver transistor bias current. With the amp at room temp. and no input signal measure the dc voltage across R12 and R13. Adjust TR1 to obtain about 81mv across one of these resistors. These were really good amplifiers, and could take a lot of abuse. Good luck, Bill Christian Technology "James Sweet" wrote in message news:v42Ed.3287$ig7.1062@trnddc04... Just took in a QSC 1700 stereo power amplifier with a dead channel. This is a typical large (500W/chan) power amp and some quick checks reveal a bunch of shorted output transistors. Are there any tricks or quirks to this particular amp? Also does anyone know the procedure for adjusting the bias? |
#3
|
|||
|
|||
"Bill Renfro" wrote in message ... No real tricks just be sure to change the transistors in pairs. You will need to remove them to test them. I would also check the driver transistors Q1&2. If you do not have a distortion analyzer you set the bias by monitoring the driver transistor bias current. With the amp at room temp. and no input signal measure the dc voltage across R12 and R13. Adjust TR1 to obtain about 81mv across one of these resistors. These were really good amplifiers, and could take a lot of abuse. Thanks, turns out the driver transistors are fine, I checked them out of circuit. Q1 and Q2 appear to be the only problem, not sure why they popped but I did notice they had no heatsink compound on them. I'll replace them and check the bias and see how it does. Seems like a well made amp, build like a tank and very easy to work on, more power than I'd ever need though. |
#4
|
|||
|
|||
Bill Renfro wrote: No real tricks just be sure to change the transistors in pairs. How do you change transistors in "Pairs" on a large pro amplifier? Answer is you don't. when you have 6,8,10,12 output transistors per channel they are not really are not paired up. But they all share current and equalize through the low value emitter resistors. When you have multiple finals shorted, you should replace them all. If you don't, chances are the other were damaged and will cause the amp to fail shortly in the future. Sure, you can change out only the shorted devices, but do you feel lucky? You should pay close attention to ANY low value resistors in the output stages for value. I would use your DMM and check them all for value to be safe. Bob You will need to remove them to test them. I would also check the driver transistors Q1&2. If you do not have a distortion analyzer you set the bias by monitoring the driver transistor bias current. With the amp at room temp. and no input signal measure the dc voltage across R12 and R13. Adjust TR1 to obtain about 81mv across one of these resistors. These were really good amplifiers, and could take a lot of abuse. Good luck, Bill Christian Technology "James Sweet" wrote in message news:v42Ed.3287$ig7.1062@trnddc04... Just took in a QSC 1700 stereo power amplifier with a dead channel. This is a typical large (500W/chan) power amp and some quick checks reveal a bunch of shorted output transistors. Are there any tricks or quirks to this particular amp? Also does anyone know the procedure for adjusting the bias? ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
looking for alpine MRV-100M or similar model amplifier schematic | Electronics Repair | |||
WARNING. DeWALT And Black and Decker Tools causing serious Injury and Death. | Woodworking | |||
WARNING. DeWALT And Black and Decker Tools causing serious Injury and Death. | Electronics Repair | |||
WARNING. DeWALT And Black and Decker Tools causing serious Injury and Death. | Home Repair | |||
Dewalt Recalls? | Metalworking |