I am trying to repair a Crest Vs450 power amp but I am stuck.
The amplifier itself works fine but its the protection circuitry thats giving problems. The protection will activate intermittently when just powered on, after a few minutes it will stay on.
I pulled up the amp to inspect the circuit board, and then put it back together. I double and triple checked everything so all connections are fine and there are no shorts.
When I powered the amp for the first time the MOV smoked and the breaker tripped.
I rechecked and turned on again, the fan started and MOV smoked again but the breaker didnt trip but I turned it off quickly.
I have a feeling that the amp is fine and will work but the MOV is toast for sure.
Can I just take out the MOV and run the amp without it, or is that unsafe?
Can someone help me out?
Here is the schematic, check page 14:
http://www.crestaudio.com/media/schematics/vvs_schematic_set1.pdf
Thanks
Lawrence
The amplifier itself works fine but its the protection circuitry thats giving problems. The protection will activate intermittently when just powered on, after a few minutes it will stay on.
I pulled up the amp to inspect the circuit board, and then put it back together. I double and triple checked everything so all connections are fine and there are no shorts.
When I powered the amp for the first time the MOV smoked and the breaker tripped.
I rechecked and turned on again, the fan started and MOV smoked again but the breaker didnt trip but I turned it off quickly.
I have a feeling that the amp is fine and will work but the MOV is toast for sure.
Can I just take out the MOV and run the amp without it, or is that unsafe?
Can someone help me out?
Here is the schematic, check page 14:
http://www.crestaudio.com/media/schematics/vvs_schematic_set1.pdf
Thanks
Lawrence
The VS and CA series of crest amps suffer from a couple of very serious problems related to the power supply capacitors. 1- they used caps rated at rail voltage!! 90+ volt rails with 90Vdc caps! did similar things in other models. 2- the caps fail in everyone of these models. they leak all over the PCB and cause the board to short from top to bottom and POOF amp goes up in flames! (I have 6 on my shelfs now stinking up the place).
With ANY VS or CA series amp. pull the caps off the board and check them for leaks. some don't have vent holes and they will suddenly explode in your face! any bulged caps be wary. some caps were put on the PCB's with the vent holes facing down, the plug hits the PCB and it wont vent then the cap explodes.
Be very cautious.
I would suspect you have a shorted cap causing the issue described. Or a PCB that has been soaked and is shorting from top to bottom. it eats the epoxy on the PCB and soaks in. only way to remove it is cut the board away in that spot.
Be very certain this is or isn't the issue before proceeding.
Zc
With ANY VS or CA series amp. pull the caps off the board and check them for leaks. some don't have vent holes and they will suddenly explode in your face! any bulged caps be wary. some caps were put on the PCB's with the vent holes facing down, the plug hits the PCB and it wont vent then the cap explodes.
Be very cautious.
I would suspect you have a shorted cap causing the issue described. Or a PCB that has been soaked and is shorting from top to bottom. it eats the epoxy on the PCB and soaks in. only way to remove it is cut the board away in that spot.
Be very certain this is or isn't the issue before proceeding.
Zc
crest vs
😎 hi there!
yes it seems that your upply caps are either dry and or leaking. i had a vs 2200 and suddenly started failing to function; once i opened found that two of the ps caps had leaked and shorted everything and also ate the copper on the pcb. ive been trying to revive it but no succes yet . for the moment it is taking a brake.
good luck , hope yours its not so bad.
😎 hi there!
yes it seems that your upply caps are either dry and or leaking. i had a vs 2200 and suddenly started failing to function; once i opened found that two of the ps caps had leaked and shorted everything and also ate the copper on the pcb. ive been trying to revive it but no succes yet . for the moment it is taking a brake.
good luck , hope yours its not so bad.
Stupid question ... how do you get the cover off a Vs450? I'm having a protection fault too. I removed the obvious (round head) screws but the cover doesn't budge.
Ok so Im still having issues...
When the amp powers up it plays fine, but most times when I power it up it stays in protection mode.
I have checked and replaced all elec. capacitors and replaced the big power supply filter caps.
There is no DC on the output, and I get 0.5V on the base of the output transistors.
Transistor Q1 does not have any voltage on the base (just a few mV) so I know there is no clipping signal that may be locking up the amp.
Any ideas on what else I should check?
Thanks all.
When the amp powers up it plays fine, but most times when I power it up it stays in protection mode.
I have checked and replaced all elec. capacitors and replaced the big power supply filter caps.
There is no DC on the output, and I get 0.5V on the base of the output transistors.
Transistor Q1 does not have any voltage on the base (just a few mV) so I know there is no clipping signal that may be locking up the amp.
Any ideas on what else I should check?
Thanks all.
Sometimes, over long use, a transistor can develop internal connection loss. Also I have seen that a diode shows good on a cold test but does not work in circuit.
Gajanan Phadte
Gajanan Phadte
Resurrecting an old thread...
I have a half-dozen or so of these. I've been reading that the caps go bad on the VS series. Are people only referring to the 2 (or 4) huge caps on the mainboard, or to the many smaller electrolytics as well? I replaced the huge caps on four of my amps several years ago and am wondering if I should go back and replace the smaller caps as well. Thanks!
I have a half-dozen or so of these. I've been reading that the caps go bad on the VS series. Are people only referring to the 2 (or 4) huge caps on the mainboard, or to the many smaller electrolytics as well? I replaced the huge caps on four of my amps several years ago and am wondering if I should go back and replace the smaller caps as well. Thanks!
- Status
- Not open for further replies.