I just picked up a carver mxr130. I play a 1khz test tone through it and I can measure the same signal on the speaker terminals and show ac voltage around 60v with the volume all the way up. But, when I plug in speakers, I have no sound at all. Any ideas?
Have you tried both 'A' and 'B' speakers? First place I'd check would be the speaker relays. You have two of them one to switch between speaker set 'A and 'B' and the other to disconnect the speakers in case of a protection fault.
My interpretation of your symptoms is that you are seeing the output when looking with a high impedance measuring device, but lose the output when the load draws current. This is indicative of a high resistance in the output path. Primary suspects would be the relays.
When you are trying to drive speakers and are getting no output, measure the AC voltage across the speaker terminals and then measure the AC voltage at the junction of R543 & R545 (or R544 & R546). If you have good signal at the amplifier outputs (R543/R545 or R544/R546) but not at the speaker, then follow the signal path through from the amplifier output to the speakers and see where it is lost.
Note this has an output relay configuration that selects 'A' speakers, 'B' speakers, or 'A & B' speakers. In the 'A & B' position, the speakers are in series and both A and B must be connected for there to be any output. Due to this configuration, you will need to confirm that the speaker output black (-) terminal is at chassis ground when that particular speaker is selected.
When you are trying to drive speakers and are getting no output, measure the AC voltage across the speaker terminals and then measure the AC voltage at the junction of R543 & R545 (or R544 & R546). If you have good signal at the amplifier outputs (R543/R545 or R544/R546) but not at the speaker, then follow the signal path through from the amplifier output to the speakers and see where it is lost.
Note this has an output relay configuration that selects 'A' speakers, 'B' speakers, or 'A & B' speakers. In the 'A & B' position, the speakers are in series and both A and B must be connected for there to be any output. Due to this configuration, you will need to confirm that the speaker output black (-) terminal is at chassis ground when that particular speaker is selected.
Thanks for that! Good insides are welcomed!
I added an 8ohm dummy load to it this morning and the relays went crazy. So, I ordered a pair of them. I can trace the output signal all the way to the relays with the dummy loads installed. I'm going to replace them and see what happens. I'll let you know.
I added an 8ohm dummy load to it this morning and the relays went crazy. So, I ordered a pair of them. I can trace the output signal all the way to the relays with the dummy loads installed. I'm going to replace them and see what happens. I'll let you know.
Relays going nuts indicates the the protection circuitry is likely to be the problem, I doubt its the relays themselves, they just do what they are told.
Connecting an 8 ohm dummy load makes the relays go crazy, but connecting an 8 ohm speaker does not? That's strange.
Could also be a power supply that is sagging under load.
Could also be a power supply that is sagging under load.
Measure for DC before the relays. If there is DC that indicates a supply fault or presumably blown output drivers.
Went back to this, this morning. Checked the power supply. 61.1 volts. Bias is 5mV both channels. Again, I plugged in my dummy loads and fed it a 1khz signal. This time the relays stayed on and again, I could measure 1khz coming out. So, I plugged the speakers back in and got very low, very distorted sound. I'm leaning hard on bad relay contacts.
Hi rodner,
The original speaker relays are known to be problematic (they were crap). So replacing them requires good new ones, not Ebay sourced ones.
The MXR-130 doesn't run the speakers in series to the best of my knowledge. I've never had occasion to check this out, but I can since I have one in the shop right now. That's once it's number comes up.
The power supply in this unit is special compared to other brands of amplifiers. I think there is one stage of commutation, and that means you will measure a lower voltage on the output collectors. Once your audio signal gets igh enough they will switch to the higher rail. Beware, it does deliver every watt it claims to deliver. Another thing to be really aware of is that the regulator maintains the DC rails at the same voltage as the load increases. That means that a high impedance AC mains supply will cause it to draw excessive current and probably lead to damage in the primary regulator circuit.
DO NOT, EVER, SHORT THE TRIAC OUT !!!!!!!
The triac is used as the AC power regulator. Shorting it will cause extremely high current to flow, and probably cause excessive damage to the receiver. This is because the power supplies would run up to extremely high voltages far beyond what the circuitry was designed to handle.
Protection circuit. It monitors the output conditions, like output current. It also measures all the power supply rails for the amplifier and also for unbalance. There is a "protect" light that will come on if it does go into protection, so there won't be any doubt. Another characteristic of protect mode is that it will cycle powering on and off continuously. Once the fault has cleared it would power up as before.
-Chris
The original speaker relays are known to be problematic (they were crap). So replacing them requires good new ones, not Ebay sourced ones.
The MXR-130 doesn't run the speakers in series to the best of my knowledge. I've never had occasion to check this out, but I can since I have one in the shop right now. That's once it's number comes up.
The power supply in this unit is special compared to other brands of amplifiers. I think there is one stage of commutation, and that means you will measure a lower voltage on the output collectors. Once your audio signal gets igh enough they will switch to the higher rail. Beware, it does deliver every watt it claims to deliver. Another thing to be really aware of is that the regulator maintains the DC rails at the same voltage as the load increases. That means that a high impedance AC mains supply will cause it to draw excessive current and probably lead to damage in the primary regulator circuit.
DO NOT, EVER, SHORT THE TRIAC OUT !!!!!!!
The triac is used as the AC power regulator. Shorting it will cause extremely high current to flow, and probably cause excessive damage to the receiver. This is because the power supplies would run up to extremely high voltages far beyond what the circuitry was designed to handle.
Protection circuit. It monitors the output conditions, like output current. It also measures all the power supply rails for the amplifier and also for unbalance. There is a "protect" light that will come on if it does go into protection, so there won't be any doubt. Another characteristic of protect mode is that it will cycle powering on and off continuously. Once the fault has cleared it would power up as before.
-Chris
Hi rodner,
I think that Digikey has them on hand (not unless they dropped those too). Let me look to see if I can find it. You need both.
-Chris
I think that Digikey has them on hand (not unless they dropped those too). Let me look to see if I can find it. You need both.
-Chris
Its a common enough failure mode by all accounts, old dried-out caps in protection circuit/module itself cause erroneous protection triggering.
Hi rodner,
Don't go changing stuff en mass until you have the problem sorted out. Mark is correct about some of those capacitors by now though. The rule of thumb would be to replace only what you have to to get it working. Once that is done and you have the receiver running you can change capacitors a section at a time and confirm you haven't caused any problems.
Rule #1 for changing capacitors. If the capacitor doesn't fit where the old one did, you can not use it. The same holds true for leads large enough to not fit in the holes.
-Chris
Don't go changing stuff en mass until you have the problem sorted out. Mark is correct about some of those capacitors by now though. The rule of thumb would be to replace only what you have to to get it working. Once that is done and you have the receiver running you can change capacitors a section at a time and confirm you haven't caused any problems.
Rule #1 for changing capacitors. If the capacitor doesn't fit where the old one did, you can not use it. The same holds true for leads large enough to not fit in the holes.
-Chris