Tweet
Complaint was a bad smell when played at high volume. I ran it on the bench under load at about 1/3 power fo 4 hours. It got warm enough to have a bit of a smell, but nothing was getting too hot. The power supply resistors R155, 156 and 157 were operating at about 150 degrees F + according to my heat gun. I checked the speaker wire and it was not reading a steady resistance when I jiggled it so I replaced it. I called it a day and put it back together. When I tried it out the sound was raggety and distorted. I re-checked the speaker connection I had just made and it checked good. I opened the amp up again and R112, the resistor across the coil L1 was burned. Previously it was fine. What could cause that resistor to burn? And concerning the output circuit, how does the speaker get the output from the power amp? I'm not seeing it. Of course it's not the first time I've missed something, but I'm stymied. Any help greatly appreciated!Stage 100-160 DSP .pdf
-
-
Thats a typical issue with those. It's a very common issue and i suspect a design flaw. Play it loud and that will happen every time.Originally posted by booj View Post -
Check to see that the choke is securely soldered to the board, the resistor should be shunted by the choke and should not burn up. Also check for high frequency oscillation. Make sure that the Zobel filter components are okay, R110, R111 and C61.Originally posted by booj View Post
The speaker is connected to the power supply center tap, just a different design approach. Fender calls this a "Flying Rail" design.Comment
-
What causes the resistor across the coil to burn? The coil not being there to conduct the majority of the current. If the coil has cracked solder at one end, or if the coil has a broken lead at one end, this will happen. The coil is a piece of wire, so it has VERY low resistance. Put your ohm meter across the 10 ohm R112. If it says 10 ohms, then the coil is open or disconnected. Normally that 10 ohm resistor will read as "shorted."Education is what you're left with after you have forgotten what you have learned.Comment
-
It is possible you have an oscillation problem. You mentioned it worked fine with dummy load, but then sounded "raggedy and distorted" and overheated the resistor when the speaker was connected.
Try connecting the scope to the speaker to see if there is an oscillation problem.Originally posted by Enzo
Comment
-
Thankyou Daz, for your reply. Is there a common cure?
52 Bill, will do. After I posted, I immediately thought probably some kind of lying rail design. the symbols they use on the scat are what confused me. They remind me of ground symbols.
Enzo, I thought that too, but the resistance across the coil read basically a short, which of course doesn't mean anything. I'll lift the board and look at / re-flow the solder connections.
g-one, will do.
thanks for your help guys. It gives me a good starting point. Appreciate it.Comment
-
On this amp, you may see connections on circuit board broken, the arcing causes a smell.
Check large capacitors and other large components for broken or cracked solder joints.
Glue down capacitors, after re-soldering them...so they won't break off the board again.
After re-soldering, it's a pretty good sounding amp, actually.Comment
-
Thank you soundguruman, I did just that. The problem turned out to be L1 had let go on one end. Had a big halo around one connection. Cleaned and re-flowed it and replaced R112.Comment
-
Any big parts on the board, like the tall filter capacitors:Originally posted by booj View Post
Glue them down so they won't shake off and break the solder connections.
This is why the amp fails quite often...
For some reason Fender did not glue those parts down to the board...
on other amps, they did.
Anywho, it's pretty good sounding amp for a solid state.
Fender SS amps seem to last just about forever. Who would have guessed?Comment
Comment