Yamaha GA-15 Guitar Amp

Status
Not open for further replies.
Jump to Latest
#2
I don't have the manual, but for a basic practice amp like this, if it is "dead", meaning no sign of life at all, you may get by without one. Pull the plug from the wall outlet, but turn the amp power switch on. Now measure resistance with your meter between the two main prongs of the power plug. You are measuring the power transformer primary through the power cord, fuse and switch this way. If you get an open, then check resistance right at the transformer primary wires. I don't know the resistance, but expect something like 50-200 ohms maybe. Point is we don;t want to see an open. If there is resistance instead of open, it is likely to be correct.

With plug in wall outlet, is there main voltage across that primary? And find the secondary wires, is there AC on them as well? We are checking the health of the power transformer.

If you get secondary voltages - oh I guess 25-40vAC with center tap - then it should be easy to find the main power supply. Those secondary wires will connect on the board right to either a rectifier bridge or to some discrete diodes. And the resulting DC will be filtered by a couple larger filter caps. Got DC on those?
 
#3
The amp is not really dead, but is in a coma. Fuse is OK, LED lights up and you hear a slight hum, but no signal is amplified at the entrance to the exit. Neither the speaker nor the headphones output. The signal is interrupted somewhere or the transistors are faulty. That's why I am looking for circuit diagram. thanks
 
#7
fastfolkert said:
The schematic looks fairly simple: Yustech GT-Guitars and Basses Solution.: Yamaha GA15
Try to follow the signal with a scope (input jack, first opamp, tone stack etc.) Look for bad jacks, switches etc.
Click to expand...

The blog answers
his blog is open to invited readers only
http://yustech.blogspot.com/

It doesn't look like you have been invited to read this blog. If you think this is a mistake, you might want to contact the blog author and request an invitation.
Click to expand...

Since you seem to be able to read it, can't you just download the schematic to your computer and then upload it here?
Thanks a lot 🙂
 
#12
yustech said:
I never mentioned anything about any schematics,never had any.That post only has pictures like the rest of my blog post.Kindly ask Fastfolket about that.

Thanks for visiting.🙂
Click to expand...

Sorry for the mis-communication: I only included that link to show the actual "inside" of the amp and to "show" that the circuit must be fairly simple. I do not have any schematics.
Again, apologies for the confusion.
 
Status
Not open for further replies.
Top Bottom