Hello, I've been collecting vintage audio for around 15 years. I've recently begun the quest to try and repair some of my receivers myself.
In my search of knowledge and non-fake parts I found this site. I am hoping to be able to PM some members (RM) in the swap meet forums to buy some NOS transistors (NOS 2SA968 - 2SC2238). Thanks
In my search of knowledge and non-fake parts I found this site. I am hoping to be able to PM some members (RM) in the swap meet forums to buy some NOS transistors (NOS 2SA968 - 2SC2238). Thanks
Be sure to determine the actual cause of the problem before replacing parts.
This can often be done with a DVM while the parts remain in the unpowered circuit.
The pcbs can easily be damaged by unneeded part replacements.
Of course, you should always use deOxit D5 to clean the pots and switches before starting.
This alone can clear up more problems than you might think.
This can often be done with a DVM while the parts remain in the unpowered circuit.
The pcbs can easily be damaged by unneeded part replacements.
Of course, you should always use deOxit D5 to clean the pots and switches before starting.
This alone can clear up more problems than you might think.
Thanks for the reply! I've got a Sansui g9700 with blown output transistors on one channel. I'm going through the driver boards and one of the transistors is out of spec. So I'm going to replace all 4 in the driver boards, some out of spec resistors, and deoxit and sweep the pots. I'm trying to be extra careful with this and cover all bases due to how sensitive this circuit is in this receiver. I am still pretty much a newb with this, but I'm learning.
Hi dr_glove,
What do you mean by "out of spec"? How are you testing it?
As Ray mentioned, you can easily cause more damage by replacing parts needlessly, or not getting all the bad ones and causing even more damage. I get stuff in all the time that was attempted. A G-9700 is too nice to wreck.
Also, use current parts bought from an authorized distributor. There are too many fakes and pulls out there. Most people don't test parts for leakage, not with sensitive enough instruments (the cheap digital transistor checkers are not sensitive enough). At higher voltages (bigger receivers) it doesn't take much to wipe a lot of stuff out.
Anyway, a nice set. Don't reach beyond your grasp.
What do you mean by "out of spec"? How are you testing it?
As Ray mentioned, you can easily cause more damage by replacing parts needlessly, or not getting all the bad ones and causing even more damage. I get stuff in all the time that was attempted. A G-9700 is too nice to wreck.
Also, use current parts bought from an authorized distributor. There are too many fakes and pulls out there. Most people don't test parts for leakage, not with sensitive enough instruments (the cheap digital transistor checkers are not sensitive enough). At higher voltages (bigger receivers) it doesn't take much to wipe a lot of stuff out.
Anyway, a nice set. Don't reach beyond your grasp.
I'm checking the transistors voltage drop using the diode test on a DVM.
I would like to take this to someone who knows what they are doing, but the guy I used to take my stuff to had to retire due to eyesight issues. He couldn't recommend anyone else in South East Wisconsin so I'm trying this myself. I was a mechanic for 25 years so I have an idea how to troubleshoot problems, but this is new to me.
I got this Sansui not working from the original owner. He said it quit a few years ago and has been not used since.
It has an open 3.9 ohm resistor in the soft start board and blown output transistors in one channel. I have found out that this usually is caused by a problem with the bias voltage due to issues with the driver boards. So I'm testing every component in those.
I've found one 560 ohm resistor that's at 300 ohms and a 2SA968 transistor that has a high voltage drop from base to emitter.
Thanks for taking the time to respond.
I would like to take this to someone who knows what they are doing, but the guy I used to take my stuff to had to retire due to eyesight issues. He couldn't recommend anyone else in South East Wisconsin so I'm trying this myself. I was a mechanic for 25 years so I have an idea how to troubleshoot problems, but this is new to me.
I got this Sansui not working from the original owner. He said it quit a few years ago and has been not used since.
It has an open 3.9 ohm resistor in the soft start board and blown output transistors in one channel. I have found out that this usually is caused by a problem with the bias voltage due to issues with the driver boards. So I'm testing every component in those.
I've found one 560 ohm resistor that's at 300 ohms and a 2SA968 transistor that has a high voltage drop from base to emitter.
Thanks for taking the time to respond.
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Hi dr_glove,
The soft-start got taken out by the output short.
When you have shorted outputs, you always change them all on that channel, plus driver transistors. That's minimum! New mica insulators and fresh thermal compound (not for computers). Check the bias transistors and any pre-drivers.
You need a proper transistor tester! Not the one built into cheap meters. The old Heathkit IT-18 is probably the best for bench use. Other Heathkit models are just as good (better maybe) but take longer to use. I collect them. You need a good DVM, you are measuring in the mV, so 100 mV full scale is not good enough. Plus many cheap meters aren't even in tolerance for their loose specs out of the box, never mind holding the accuracy over time.
Unpopular as it might seem, you need decent test equipment and some experience. It wouldn't bother me to see someone learn on an NAD, but not a nice Sansui upper end receiver! Those can be very nice. A good tech will have the right equipment and can confirm the equipment perform at least to spec. No, you can't hear distortion on a test, but you can tell the difference when it is working right from before. I get stuff in from other shops where (it's working to spec, I can tell by ear) that measures well over 1% THD. Once fixed properly, the customers say they can't believe they thought it was okay.
Use only new, known parts. One fake or bad part can cost you everything else - plus maybe even the PCB. Wishful thinking doesn't pay.
While you're at it, get a variac. Dim bulb testers make it hard to troubleshoot and do not always prevent damage. I've tried them, took mine apart. I've always used a variac as I was trained - for good reason. You absolutely do need an oscilloscope. A THD meter is more than helpful, audio analyzers being extremely expensive (but better still).
-Chris
The soft-start got taken out by the output short.
When you have shorted outputs, you always change them all on that channel, plus driver transistors. That's minimum! New mica insulators and fresh thermal compound (not for computers). Check the bias transistors and any pre-drivers.
You need a proper transistor tester! Not the one built into cheap meters. The old Heathkit IT-18 is probably the best for bench use. Other Heathkit models are just as good (better maybe) but take longer to use. I collect them. You need a good DVM, you are measuring in the mV, so 100 mV full scale is not good enough. Plus many cheap meters aren't even in tolerance for their loose specs out of the box, never mind holding the accuracy over time.
Unpopular as it might seem, you need decent test equipment and some experience. It wouldn't bother me to see someone learn on an NAD, but not a nice Sansui upper end receiver! Those can be very nice. A good tech will have the right equipment and can confirm the equipment perform at least to spec. No, you can't hear distortion on a test, but you can tell the difference when it is working right from before. I get stuff in from other shops where (it's working to spec, I can tell by ear) that measures well over 1% THD. Once fixed properly, the customers say they can't believe they thought it was okay.
Use only new, known parts. One fake or bad part can cost you everything else - plus maybe even the PCB. Wishful thinking doesn't pay.
While you're at it, get a variac. Dim bulb testers make it hard to troubleshoot and do not always prevent damage. I've tried them, took mine apart. I've always used a variac as I was trained - for good reason. You absolutely do need an oscilloscope. A THD meter is more than helpful, audio analyzers being extremely expensive (but better still).
-Chris