Issue with SA-7800

R

Ryan Walton

Active Member
Hi this is my first thread here at AK. I want to apologize in advance for my lack of electronics knowledge. I'm currently learning which is part of the reason why i'm posting today.

I came across a Pioneer SA - 7800 and TK-7800 at the thrift store the other day.
20180727_000844_1.jpg



Upon getting it home, it worked great with the exception of the power indicator lamps not turning on. Until yesterday, that is. Now, the SA-7800 has gone silent on me. All the displays work, and speakers are connected, but just no sound.

So I started some researching and learned a bit from this thread: http://audiokarma.org/forums/index.php?threads/pioneer-sa-7800-no-sound.470671/ Alot of great info there which was very helpful to me. I believe I might be experiencing the same issue with the protection mode staying on. My first question is... how do I know if protection mode is on or not because there is no indicator or beeping sound regarding it. My second question is, how do I get out of protection mode if the SA-7800 is indeed stuck in it?

I wanted to let you guys know i'm also utilizing a Cen-Tech 7 function digital multi-meter. My third question is, this multi-meter sufficient for checking the voltages on the SA-7800? Also, could someone please explain to me the process for checking the voltages for the for the different capacitors and transistors on the SA-7800? (Again, I apologize for my lack of knowledge but I am trying to learn)
20180729_203758_1.jpg


I've been learning the basics of using a multi-meter from watching this video...
and I've also managed to get ahold of the Service & Manuals & Schematics on the SA 7800. I even picked up a soldering iron and some resin based soldier in case I need to do some refreshing on the soldier joints or recapping. If any of you professionals can guide me in a direction i'm willing to do whatever it takes to restore this great system again.
 
if the power meters are working normally it is out of protection .
you may have knocked the tape monitor switch or something .
 
petehall347 said:
set the top toggle switches to centre . and all lower ones up . select correct speaker setting .
Click to expand...
By top toggle do you still mean the tape switch? That is definitely in the middle or "off" selection. Speakers selection is correct and im currently on aux line.
 
petehall347 said:
and can you confirm the meters moving with the sound ?
Click to expand...
Im not getting any meters bouncing from the sound at all since it went silent on me a couple of days ago. All the settings are correct and ive tried multiple different speakers...but something has decided not to work anymore.
 
you should hear the relay click a few seconds after after powering the amp on .
if no click this amp is not for beginners to learn on as its a NSA amplifier and can be very finicky .
 
petehall347 said:
you should hear the relay click a few seconds after after powering the amp on .
if no click this amp is not for beginners to learn on as its a NSA amplifier and can be very finicky .
Click to expand...
No click....could this be a situation where there is a crack in one of the transistor joints?
 
I understand some of this may be difficult, but ive really fallen in love with the system so i believe i can do this if someone is willing to point me in a direction based on the symptoms ive discussed.

Im 36 and pretty good at following directions and not totally clueless when it comes to electronics. I have built multiple personal computers. Im just unfamiliar with soldering and circuitry. I have a feeling the problem lies in a bad soldier with either a transistor or capacitor...
 
on the main amp are coils L1 and L2 . these are in parallel with 10 ohm resistors . you need to you set meter on DC volts . black probe to shiny chassis red to those resistors legs . doesn't matter which end so long as its a good connection . these should ideally measure zero volts . report back with your results .
p.s tape up the probes so just the tips are showing to reduce the risk of shorting something out .
 
petehall347 said:
on the main amp are coils L1 and L2 . these are in parallel with 10 ohm resistors . you need to you set meter on DC volts . black probe to shiny chassis red to those resistors legs . doesn't matter which end so long as its a good connection . these should ideally measure zero volts . report back with your results .
p.s tape up the probes so just the tips are showing to reduce the risk of shorting something out .
Click to expand...

Sounds good I will start on this later tonight after work. Should i use electrical tape or does it matter?
 
petehall347 said:
on the main amp are coils L1 and L2 . these are in parallel with 10 ohm resistors . you need to you set meter on DC volts . black probe to shiny chassis red to those resistors legs . doesn't matter which end so long as its a good connection . these should ideally measure zero volts . report back with your results .
p.s tape up the probes so just the tips are showing to reduce the risk of shorting something out .
Click to expand...

Also I'm assuming the everythint has to be turned off while testing voltage correct? When you say shiny chassis what do you mean?
 
yes insulation tape will do . i use wire shrink wrap on mine .
no it has to be switched on . be aware of high voltages .
i mean the chassis that isnt painted .. the metal case in other words
 
Okay just a few pics here to make sure were on the same page... here's the schmatic... i think i've found the coils you're talking about on the diagram... is this correct? (see highlights)
L1_L2.jpg


Now is this the area I should be putting the black probe? (See yellow circle, unpainted area)
Inked20180730_202433_LI.jpg


Finally... if that is the correct area you were talking about... where exactly are the coils or resistor legs? Are they in this picture?
20180730_202458.jpg
 
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