Evh 5150 iii 2x12

[Evh5150]

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.

It is exactly like photo 2, on that board there is a Zener diode, the 2 double potentiometers and 2 polyester capacitors is an external board.

The pcbs are of very low quality and you have to be careful only when soldering and desoldering. In fact, I will have to repair some tracks from board to board and because k3 doesn't have them.

[Evh5150]

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

I found something strange when I close the volume potentiometer ch2 the k6 opens and when I turn it to raise it closes it is strange, what causes that I don't know, what happens is a signal that comes from wj62.

[g1]

I found something strange when I close the volume potentiometer ch2 the k6 opens and when I turn it to raise it closes it is strange, what causes that I don't know, what happens is a signal that comes from wj62.

Which half of K6, or both halves? Is it the exact same part number as the original?
The direction of the signal does not 'come from' wj62, it goes from WJ61 > K6 > WJ62 > K2

[Evh5150]

Which half of K6, or both halves? Is it the exact same part number as the original?
The direction of the signal does not 'come from' wj62, it goes from WJ61 > K6 > WJ62 > K2

from the power pins, on both sides it stops doing the function, all the relays are the same, I bought 10 and I had the ones that had the board left, if I don't remember wj62 connects to the pcb where k6 is and then it is connected to the central plate which reaches a Zener diode I'm going to take photos and upload.

Thanks again, I looked for support in your time and fender had it for me for 3 months and they could not solve the problem where I live. Fender's support is of poor quality.

[Evh5150]

from the power pins, on both sides it stops doing the function, all the relays are the same, I bought 10 and I had the ones that had the board left, if I don't remember wj62 connects to the pcb where k6 is and then it is connected to the central plate which reaches a Zener diode I'm going to take photos and upload.

Thanks again, I looked for support in your time and fender had it for me for 3 months and they could not solve the problem where I live. Fender's support is of poor quality.

The weird thing that goes from nc to no when I lower the volume from ch2 to 0.

[Delta362]

I would check the wiring on sheet 4 to the coils of the relays (K3, K5, K6). When you are turning down Channel 2 volume, are all three relays toggling, or just K6? Make sure you don't have a miswire on the WJ pinouts shown below, plus what you showed above from sheet 1. I suspect it's a jumper wire in the wrong spot. See where you are losing the coil control voltage.

[Evh5150]

I would check the wiring on sheet 4 to the coils of the relays (K3, K5, K6). When you are turning down Channel 2 volume, are all three relays toggling, or just K6? Make sure you don't have a miswire on the WJ pinouts shown below, plus what you showed above from sheet 1. I suspect it's a jumper wire in the wrong spot. See where you are losing the coil control voltage.

Can the amp be tested without the tubes on?

I understand that what should always be connected is the speaker.

I checked the voltage of all the relays the other day and they all had 14v.

Here I bought the relays and they are the same ones that the amplifier has. I leave the page where the relay data is.

https://www.digikey.com/en/products/...2503156

[g1]

Can the amp be tested without the tubes on?

I checked the voltage of all the relays the other day and they all had 14v.

I think in standby mode, the relays and switching can still be tested.
Did you measure the 14V between pins 1 and 16 of the relays? For 24V relays, 18V is the minimum reliable switching voltage, so I don't think they would run them on 14V.

[Evh5150]

I think in standby mode, the relays and switching can still be tested.
Did you measure the 14V between pins 1 and 16 of the relays? For 24V relays, 18V is the minimum reliable switching voltage, so I don't think they would run them on 14V.

I found something, I measured k2 when activating ch3 and I have 25v on the relay, I checked the power of the other relays and I have 14v when activating ch2, I started to check the values of the resistors I found that R84 has a value of 1.2k and in the schematic It has 220 ohms, tomorrow I'm going to change it and check the voltages again, check the transistors and everything you told me in a previous answer.

Thanks for the help, I'm not very advanced in electronics, my study brother has been guiding me in conjunction with what you tell me.

because channel 1 does not present the same problem because the relay is in NC in the chain when turning on.

[Evh5150]

I found something, I measured k2 when activating ch3 and I have 25v on the relay, I checked the power of the other relays and I have 14v when activating ch2, I started to check the values of the resistors I found that R84 has a value of 1.2k and in the schematic It has 220 ohms, tomorrow I'm going to change it and check the voltages again, check the transistors and everything you told me in a previous answer.

Thanks for the help, I'm not very advanced in electronics, my study brother has been guiding me in conjunction with what you tell me.

because channel 1 does not present the same problem because the relay is in NC in the chain when turning on.

I changed resistor R84 and the tone worked but since it's late I looked at the mini card there is a loose cable so tomorrow I'll let you know if the volume of channel 2 works but the tone of ch2 already works, also as I take out of a board of one pc source the 220 ohm resistor tomorrow I buy one.

I have a question, I measured k3 and it is giving me 27 volts.

[g1]

I have a question, I measured k3 and it is giving me 27 volts.

K3 is now measuring 27V where it measured 14V before? Then 220R is too low a value for R84. You found R84 was 1K2, is that what it's color code showed as well? (brown, red, red) Maybe try 330R or 470R.
The schematic may not be a perfect match, and it's possible the amp was originally working properly with 1K2 for R84. It's also possible the problem is with Q8 or Q10 and adjusting R84 is not the real solution.

[Evh5150]

K3 is now measuring 27V where it measured 14V before? Then 220R is too low a value for R84. You found R84 was 1K2, is that what it's color code showed as well? (brown, red, red) Maybe try 330R or 470R.
The schematic may not be a perfect match, and it's possible the amp was originally working properly with 1K2 for R84. It's also possible the problem is with Q8 or Q10 and adjusting R84 is not the real solution.

I rewired the panel where k6 is to verify that the resistance change is good and now activate the gain and volume, I'll be checking if it fails inside the cabinet.

but the relays gave 14v before placing 220 ohm in R84 and then 27v but in k6 I got exactly 25v. The multimeter may be giving wrong values.