Issue with SA-7800
- Thread starter Ryan Walton
- Start date
Ryan Walton
Active Member
Alright well I'll look for it more tonight there's not a picture of these coils anywhere is there?
petehall347
the brandy coffee man
they are next to the relay .
Ryan Walton
Active Member
Okay this step is complete! Both resistors did in FACT measure zero volts!
petehall347
the brandy coffee man
that is good then . just turning in for the night so will catch up tomorrow
loweran
Super Member
Take a pic of your amp board and post it. Get close ups of both sides. There is a pattern that I discovered on these where the outputs short and take out specific resistors. As others have said, this one is not a beginner unit. It takes some patience and a lot of holding your mouth just right to get it back into working order.
Ryan Walton
Active Member
Ryan Walton
Active Member
Ryan Walton
Active Member
Ryan Walton
Active Member
If you need anything else specific please let me know
Ryan Walton
Active Member
Other another thing I noticed when it was still working and I would turn it on it would not turn on right away like it would be slower and slower to get the actual tuner going.... like I said all the indicators work but there is no sound on it and the sound meters do not go up at all regardless of turning up the volume it remain silent
loweran
Super Member
Good! I don't see the burnt resistors like mine.
Do you have a dim bulb tester? If not, do a search on them and build one. It will save you from smoking the amp when you work on it. You will need to get some voltage measurements to move forward. In the mean time, you can inspect the boards for cold / cracked solder joints and reflow them. There were two transistors on my phono amp that had removed themselves.
Here is a link to my restore thread: http://audiokarma.org/forums/index.php?threads/sa-7800-restore.797285/
Look at post 13 for some good reading. This is how I discovered that this issue common.
If you are tempted to try and set the DC idle current, DONT! You need to install new trimpots. DONT move the existing ones. I think that is the cause of the smoked resistors and outputs. Tarior has a good write up on that here: http://audiokarma.org/forums/index.php?threads/sa-7800-how-to-not-make-one-into-a-doorstop.752089/
You can hook up your MM and see where the voltages are now. It may be why you are in protection. Download the service manual and look at page 11 to see how to take those measurements. Just do not attempt to adjust them by turning the VRs mentioned on the page, just get the current readings.
Do you have a dim bulb tester? If not, do a search on them and build one. It will save you from smoking the amp when you work on it. You will need to get some voltage measurements to move forward. In the mean time, you can inspect the boards for cold / cracked solder joints and reflow them. There were two transistors on my phono amp that had removed themselves.
Here is a link to my restore thread: http://audiokarma.org/forums/index.php?threads/sa-7800-restore.797285/
Look at post 13 for some good reading. This is how I discovered that this issue common.
If you are tempted to try and set the DC idle current, DONT! You need to install new trimpots. DONT move the existing ones. I think that is the cause of the smoked resistors and outputs. Tarior has a good write up on that here: http://audiokarma.org/forums/index.php?threads/sa-7800-how-to-not-make-one-into-a-doorstop.752089/
You can hook up your MM and see where the voltages are now. It may be why you are in protection. Download the service manual and look at page 11 to see how to take those measurements. Just do not attempt to adjust them by turning the VRs mentioned on the page, just get the current readings.
petehall347
the brandy coffee man
offsets are ok . problem is power supply or protect circuit . possibly a cracked solder joint .
petehall347
the brandy coffee man
yes there is over-current protection .. q27 q28
Ryan Walton
Active Member
So just to clarify....am i in protection mode? If so, how do i get out of it? And are there any particular joints i should definitely reflow or do all?
Ryan Walton
Active Member
And again, please forgive my lack of knowledge here but ive never had to actually reflow a solder joint...would i basically dissolder the entire component and reflow or can i simply flow the new solder over the existing to try and make a better connection?
Are there any good video tutorials out there on how to do this? I do have my solder iron and resin based solder ready to go...
Are there any good video tutorials out there on how to do this? I do have my solder iron and resin based solder ready to go...
petehall347
the brandy coffee man
slow down a little .
on the power supply there are transistors that fasten to small heat sinks . check the soldering on those first to look for cracks in the solder .
if any are cracked its best to remove the old solder then solder again with 60/40 cored solder .
on the power supply there are transistors that fasten to small heat sinks . check the soldering on those first to look for cracks in the solder .
if any are cracked its best to remove the old solder then solder again with 60/40 cored solder .
petehall347
the brandy coffee man
if no joy there its best to start looking at the supply voltages .
Ryan Walton
Active Member
Okay thanks pete i will take a look at this tonight....and when you say "power supply" on this amp...what component(s) are you specifically referring to? The big black box in upper right or?
Also, is it confirmed im in protection mode? If so, how did i get into it?
Also, is it confirmed im in protection mode? If so, how did i get into it?