Evh 5150 iii 2x12

[Evh5150]

Hello, I want to ask for help, I bought an EVH 5150 III and the blue channel is failing, I changed all the relays and the volume of channel 2 does not work for a strange reason, it works with the volume of channel 1, I sent an email to evh, they did not send me the Exact schematic but they assure that it is the one used by my amplifier, I am going to add it.

I'd appreciate your help.

[g1]

Blue is 2. The schematic just goes by number so please use the numbers, not the colours.

1 and 2 are shared controls. I think you are saying 1 works, but when you select 2 there is no sound?

[The Dude]

Ha! I'm working on one of those at this very moment, but different problem. The OT bolts/screws came loose during shipping. The transformer was rolling around in the cabinet, screws rolling around in the chassis, and wires are broken. What a pain this is. You have to remove the entire main board to access chassis holes and reinstall the transformer.

[Evh5150]

Hello, I want to ask for help, I bought an EVH 5150 III and the blue channel is failing, I changed all the relays and the volume of channel 2 does not work for a strange reason, it works with the volume of channel 1, I sent an email to evh, they did not send me the Exact schematic but they assure that it is the one used by my amplifier, I am going to add it.

I'd appreciate your help.

I checked the k3 relay and it has cold soldering and the tracks also came out I have to rebuild, but the amplifier shows that the volume of channel 2 does not work, it works with the volume that corresponds to channel 1 it is strange and when I tap the k3 relay This activates the gain of channel 2 accordingly, before changing the relays. After about 10 minutes playing on channel 3, it returned to 2 and this channel was left without gain.

The original number of the amp is P/N 7713071000 REV A, I couldn't find the schematic and I sent an email to evh and they sent me the attached one, I don't know if the schematic exists with that number.

I stay tuned, regards.

[Evh5150]

Blue is 2. The schematic just goes by number so please use the numbers, not the colours.

1 and 2 are shared controls. I think you are saying 1 works, but when you select 2 there is no sound?

When the amp hits k3, it activates the gain but the volume of ch2 cannot work, it is using the volume of ch1, it is strange, I understand that a chain activation is generated, but some relay is not fulfilling its function, change all the relays, they are new.

Thanks for your answer.

[Evh5150]

Ha! I'm working on one of those at this very moment, but different problem. The OT bolts/screws came loose during shipping. The transformer was rolling around in the cabinet, screws rolling around in the chassis, and wires are broken. What a pain this is. You have to remove the entire main board to access chassis holes and reinstall the transformer.

You must be very careful with these amplifiers, the one I have has low-cost materials to be worth 2000 usd, the board is of poor quality, be very careful with the temperature of the soldering iron because the tracks rise easily, I have to rebuild the area where I think There is the problem using even rivets to join one face with another.

[The Dude]

My "project" is already done and back together. I recommend, if you already have the main board out of the unit, checking the output transformer screws. The unit I have on my bench had screws just long enough to reach the transformer plate's threaded holes. The screws were also tapered at the ends, so I'm betting maybe only a couple of threads were catching. Not a good situation. If you already have yours apart, I'd recommend installing longer screws and a dab of Loctite or similar to hold in the OT. It will save you from having to tear the thing apart again in the future.

[g1]

When the amp hits k3, it activates the gain but the volume of ch2 cannot work, it is using the volume of ch1

I'm not sure I understand.
The volume is a dual pot. How do you know it is using the volume of ch.1 ? Relay K6 selects which section of the volume pot is in use.

[Evh5150]

I'm not sure I understand.
The volume is a dual pot. How do you know it is using the volume of ch.1 ? Relay K6 selects which section of the volume pot is in use.

It is a dual potentiometer, and the volume that is working is that of channel 1 and it works for the 2 channels for a reason that I do not understand, I decided to check k3 well and I found that it had 2 less tracks that serve as a relay latch so to try I will wire those pins, supposedly the signal reaches the k6 from the yellow wj62 cable, it's time to check if k2 does its job before going to k6.

I found that the 2x1 cables that go to ground are soldered and cut without offering any function but somehow I connected them and there was no sound. The amplifier had to be cut 1 by 1 and it gave sound so I removed them now.

Thank you for answering any ideas of which sector I should review.

Greetings.

[g1]

K2 only selects between 3 or 1/2. It can't be the problem.

[g1]

It is a dual potentiometer, and the volume that is working is that of channel 1 and it works for the 2 channels for a reason that I do not understand

I'm still not sure what you mean. The 'volume' for ch.1 or 2 uses the same knob, it is a dual pot. Do you hear sound when you select ch.2 ?
If the same control is working for both channels, that is normal. Why do you say ch.2 is 'using' ch.1 volume, are you looking with a scope?

[Delta362]

The volume pot for channel 1 and 2 is a concentric pot. Did you trace your input signal thru both halves of V1 to make sure it gets to both sections of the concentric pot? Looking at the schematic, K3 would toggle between the two gain sections of the pot. Check for the soldering around it. See if K3 coil voltage is good and stable.

[g1]

The volume pot for channel 1 and 2 is a concentric pot.

That's interesting. So it has an inner and outer knob? I guess I wasn't looking at the pictures close enough. Maybe they are just stuck together in this unit?

[Delta362]

That's interesting. So it has an inner and outer knob? I guess I wasn't looking at the pictures close enough. Maybe they are just stuck together in this unit?

The original release of these amps did not have concentric pots. There was a mod available only to Fender Authorized techs for installation to change the gain and volume pots for Ch1/2 to be concentric style. They have since incorporated that into the amps as standard now.

I've uploaded an older style (5150 III combo photo) and a newer style. It's very obvious on the head with the black knobs contrasting the white ones. On some other versions of it, both the concentric knob and main knob are the same color.

[Evh5150]

The volume pot for channel 1 and 2 is a concentric pot. Did you trace your input signal thru both halves of V1 to make sure it gets to both sections of the concentric pot? Looking at the schematic, K3 would toggle between the two gain sections of the pot. Check for the soldering around it. See if K3 coil voltage is good and stable.

I will review what it tells me, it happens that I am rebuilding the back of k3, I bought the relays recently, thanks for the answer.