5
Score
Ben Eisenman
53.5k
Asked
Why won't my Amp power up?
I have an A500 Behringer power amp that will not power up. I replaced the power cord and fuse with known working ones, with no result. Next, I took the fuse I tested in it and plugged it back into a working amp of the same model, which ran fine (so I know the amp isn't just killing fuses).
Any ideas?
UPDATE:
(I would have put this as a comment, but needed more words. I would have edited my original post, but couldn't upload pics on an edit.) Every once in a long while, the lights on the front of the power amp will light briefly and then die, but 98 percent of the time, nothing. I have opened it up, and here is the power path:
There is the plug/fuse combo:
As you can see, there is a green/yellow ground. There is a black wire that goes straight into the heart (massive heavy cylinder of wires) of the amp. There is another black wire with a capacitor (I think?) directly after the plug. This wire goes to the switch in the front, which is a simple push button. There is a blue wire coming out of the switch back into the heart of the amp, completing the circuit.
The rest of the components (led board, input boards, output boards, volume knobs) seem irrelevant because it's not getting power at tall (but I could be wrong). Here's a pic of the entire setup:
Any ideas? I am not an electrician, so please use small words :)
6
Score
cody
203
Answered
Accepted Answer
I happen to live in your area. Is there a way we could meet up and I could take a look at the amp for you. You could bring it by my church either this coming new years or this saturday night. Let me know so I can come early :-)
-----UPDATE-----
I fixed it! Here is what I did:
1. Pray that God would be glorified through anything I do
2. Plug it in to make sure it doesnt just turn on, it didn't so unplug it
3. Removed and checked the front ON switch for power continuity (with power turned unplugged, just use a multimeter on continuity check.
4. Removed and checked the two fuses on each of the amplifier circuit boards
5. Removed and checked continuity of the power connector through that fuse
6. Used a multimeter to check every easily accessible diode
7. Checked to see if any of the electrolytic capacitors had "popped tops" (if they had blown)
8. Now the scary part: unplug the power cables (yellow and orange) going from the huge inductor/transf
9. Use a multimeter to check the voltages coming out of those two power cables, they should be somewhere around 70Vrms.
10. Everything checked out ok, so I turned power off. Plugged everything back in where is was supposed to be, and turned the power back on. And it worked!! There was probably a loose connection or an oxidized lead.
11. Praised the Lord for His love. :-)
0
Score
Chris Green
14.9k
Answered
try and checking the amplification circuit board, look for any anomalies in the circuit paths, or circuitry, also check any other boards in the amp as well. Is it a tube amp? if so, check the tubes for damage, or replace them (remember, change them all at once). check for any damage to the boards and see what you find, have you tried another outlet by any chance?
Good Luck,
Chris
0
Score
Answered
This amp has no tubes...
This is a grounded collector Amp. The two large caps form a center tap for the power supply which is connected to the speaker terminal. So This is cap coupled amp. Therefore if you drive high currents of low frequencies the large caps will fail...it is a very graceful failure. The signal will just fade away. The lower the impedance of your load (speakers) the faster this will happen. Replacing these caps should put you back in service...
Cap coupled amps sound bouncy...Pulses are accelerated and then fall off...So the choice of replacement cap will effect the tonal quality of the amp. The best choice would be splitting the required value over several small caps connected in parallel.
Note replacing the caps requires removing the amp circuit boards...which means disconnecting the heat sinks...lots of little bits, and heat sink paste. I would recommend replacing all the screws you remove because they will disintegrate on contact.
Replacing the twisted output wires with OFC similar temp rated wire or even untwisting the OEM wire can't hurt either.
This amp has huge potential, by design, but crippled by implementation.
I suggest taking good (clear) pictures of everything before you pull it apart. Do one side at a time. Have a container for all the bits. Avoid bending the power transistors leads once you remove the screws holding the circuit board from the heat sink.
Or just buy another one for $250