Reddish 500 EQ

[JMan]

WOW. So we are losing audio signal at or before the input transformer. Well the good news is that this seriously narrows down our search.

First let's double check, were these measurements taken with the unit engaged? I don't mean to sound pedantic, but it's better not to make assumptions.

 

[andia]

are you measuring against audio ground?
is the input transformer mounted correctly?

 

[JMan]

are you measuring against audio ground?
is the input transformer mounted correctly?

If he followed my instructions (which I hope I wrote clearly enough), he should be measuring everything after the input transformer until the primaries of the output transformer against audio ground. Let's see what he says.

The input transformer mounting is a likely culprit if those voltage readings are accurate. In fact, it could only possibly be the input transformer or the relay K1.

 

[inf0]

If he followed my instructions (which I hope I wrote clearly enough), he should be measuring everything after the input transformer until the primaries of the output transformer against audio ground. Let's see what he says.

The input transformer mounting is a likely culprit if those voltage readings are accurate. In fact, it could only possibly be the input transformer or the relay K1.

Sorry for hijacking the troubleshooting but I'm curious to know how the mounting of the input transformer affects it. I'll be assembling mine soon so it's good to know

 

[Forcemusicgroup]

WOW. So we are losing audio signal at or before the input transformer. Well the good news is that this seriously narrows down our search.

First let's double check, were these measurements taken with the unit engaged? I don't mean to sound pedantic, but it's better not to make assumptions.

yes. the unit was engaged.

 

[andia]

Sorry for hijacking the troubleshooting but I'm curious to know how the mounting of the input transformer affects it. I'll be assembling mine soon so it's good to know

if you turn it 180°...

 

[Forcemusicgroup]

are you measuring against audio ground?
is the input transformer mounted correctly?

yes I mounted against ground. I also checked the points between the transformer and its top PCB for for continuity

 

[inf0]

if you turn it 180°...

oooo . I know what you mean now!

 

[JMan]

Sorry for hijacking the troubleshooting but I'm curious to know how the mounting of the input transformer affects it. I'll be assembling mine soon so it's good to know

Well, as far as the mounting itself, you just need to make sure it's not the wrong way around (the side with the transformer pins points toward the top of the pcb). Force Music Group's pictures don't show much of his input transformer, but you can at least see that he has it oriented correctly.

 

[dmp]

Transformer could be upside down. It's symmetrical, i.e. bottom pins to top pins

 

[JMan]

yes I mounted against ground. I also checked the points between the transformer and its top PCB for for continuity

Okay, so we have narrowed it down to only two possible candidates for where the problem is, the input transformer and the K1 relay. I'm going to have you measure several things to try and drill down on this.

With the test tone on and the unit set to BYPASS, measure AC voltage first between In+ and In- on the edge connector, then between Out+ and Out-. Do you see the same signal in both places?

Now with the test tone on and the unit IN, measure between the second and third pins from the right on the right angle header on the upper (pin-side) pcb of the input transformer. Do you have the same signal here as you do on the In+/- pads?

 

[JMan]

Transformer could be upside down. It's symmetrical, i.e. bottom pins to top pins

Good point! @Forcemusicgroup did you pay close attention to matching the pin numbers on the transformer to the pin numbers on the silkscreen of the small mounting board?

 

[andia]

Transformer could be upside down. It's symmetrical, i.e. bottom pins to top pins

would that matter in a 10k:10k?

 

[JMan]

would that matter in a 10k:10k?

In this case yes, because of how the traces route through the J1 right angle header to the main pcb. It would definitely cut off the audio signal, I think. Trying to work this out in my head, but if nothing else, it breaks a ground connection.

 

[andia]

In this case yes, because of how the traces route through the J1 right angle header to the main pcb. It would definitely cut off the audio signal.

I see.

 

[JMan]

Actually, as I sit here screwing my face up trying to work that out, it looks like it would break the pin 6 connection on the transformer and connect pin 11 to ground, but the audio connections would remain intact. Still not ideal.

 

[andia]

could be the transformer itself.

 

[JMan]

Definitely could be.

@Forcemusicgroup let's start with those tests in post #391 and the question in post #392. We're zeroing in on the culprit here.

 

[Forcemusicgroup]

working on it.

 

[Forcemusicgroup]

Okay, so we have narrowed it down to only two possible candidates for where the problem is, the input transformer and the K1 relay. I'm going to have you measure several things to try and drill down on this.

With the test tone on and the unit set to BYPASS, measure AC voltage first between In+ and In- on the edge connector, then between Out+ and Out-. Do you see the same signal in both places?

Now with the test tone on and the unit IN, measure between the second and third pins from the right on the right angle header on the upper (pin-side) pcb of the input transformer. Do you have the same signal here as you do on the In+/- pads?

*in bypass*
Between In- and +In I have .158vac
Between -out and +out I have .158vac

*engaged*
.139vac