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
|
|||
|
|||
Amplifier
Hi!
I got an old SONY amplifier where the right channel seems to be defective. When I turn the balance to the right speaker, the volume gets lower and low frequencies are missing completely. I am really not sure, where I should start searching for the error. First I tried another pair of speakers, but this was not the cause. Can anyone tell me where I should start searching for the error? Can anyone tell me what the integrated preamp (I found this on the schematics) is good for? Thank you, arvid puschnig |
#2
|
|||
|
|||
Amplifier
"Tweetldee" wrote: Posting a copy of the schematic would definitely help. It eliminates a lot of guesswork. Ok, I'll put it up the next 2 days. First thing you should do is to check voltages around the output stage of the defective channel. If the schematic shows voltage readings, use them as a guide for troubleshooting. As a backup, since the other channel is working, you have a good source of voltages/resistances built right into the unit. Use the other channel as a comparison when you get into an area where the voltages are way out of whack. Start at the output stage and work your way back to the input of the power amp. You should find a stage where the voltages are very wrong. Concentrate there. Do I have to check voltages with an input signal or with load (speakers connected)? When you have found that stage, turn it off and check all semiconductors in that area. If the amp stages are DC coupled, remember that the incorrect voltages may cascade down the chain, so keep that in mind while you're working. I am not sure if the stages are DC coupled, but since I could not find a capacitor in the signal way I would say they are. Perhaps you can have a look at the schematics then. There's a label at the front of the amp "All power stages direct coupled"... Use the diode check function of the ohmmeter in the DMM to check semiconductor junctions. In some circuits, you may have to remove the semiconductors to get meaningful readings, especially if the stages are DC coupled or if there are very low-value resistors in the neighborhood. Ok. Why don't you post a decent scan of the schematic and then take some voltage measurements around the bad channel, and post those here in the group. Then we can get to work. I'll put it up tomorrow and at the weekend I'll take voltages. Thanks for your help! arvid |
#3
|
|||
|
|||
Amplifier
First thing you need to do is try and determine if the problem is in the
pre-amp stage or power amp stage. Looks like you have a good break point at R500/R550 for one channel and the equivalent point for the other channel. Manually swap the pre-amp stage to power amp signal between the left and right channel at those resistors and see if the symptom stays with the right channel (power amp problem) or moves to the left channel (pre-amp or earlier problem). Note I am not talking about what Sony calls the pre-amp transistors in the power amp stage as shown on the schematic, but the actual pre-amp before the power amp board. I would also suspect any electrolytic capacitors in the signal path, like c500/550 for one due to the extreme age of the unit. C505/555 would also be suspect due to its location in the feedback path. Due to the age I would probably start with the capacitor ESR meter as capacitors commonly go bad with age. There are not that many to check and it owuld rule out one common failure source. David Arvid Puschnig wrote in message y.telekom.at... "Arvid Puschnig" wrote: Ok, I'll put it up the next 2 days. Ok, here it is: http://www.sbox.tugraz.at/home/a/arvid/TA-AV501R/ It's the schematics of the Speaker Board and of the Power Board. Please tell me if file sizes and quality are ok... arvid |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
transistors in amplifier ear | Electronics | |||
good books on amplifier construction | Electronics | |||
Simple Amplifier Needed | Electronics | |||
Battery powered amplifier from car speakers and booster amp? | UK diy | |||
Technics SA-TC30 amplifier | Electronics Repair |