Reddish 500 EQ

[JMan]

Okay, now that my head is a bit more clear (albeit still a little foggy), I'm guessing the impedance measurements are drifting because ultimately you are measuring a path that runs through a capacitor - the electrolytic on the output amp. The inductors may also be affecting it, I am not sure. At any rate, if you leave the probes in place, does the reading eventually stabilize? All we're trying to do is hunt for a short somewhere in the circuit.

 

[Forcemusicgroup]

does not stabilize. Just drifts.

 

[capacitorless]

I don't want to get in the way of JMan's generous assistance, but does it make any sense to remove that cap temporarily to take the measurements? Not sure how difficult that would be.

 

[JMan]

does not stabilize. Just drifts.

Can you be more specific? I mean, are we talking about a slow steady creep of a few ohms, or are we talking about quickly jumping around in large leaps from hundreds of ohms to thousands and back again? (Or something different?) And how long are you watching the meter drift before you remove the probe? It sounds to me like a capacitor is charging from the small current that your multimeter is providing but "drift" is not precise enough to be sure we're understanding the same thing.

Did you redo the continuity tests with the module removed from power?

I don't want to get in the way of JMan's generous assistance, but does it make any sense to remove that cap temporarily to take the measurements? Not sure how difficult that would be.

Please feel free to get in the way! I think Forcemusicgroup is a relative beginner (no judgement, we all start as beginners) and isn't sure how to go looking for problem spots on his own, so any thoughts on what might be going on are welcome as we try to find the issue.

That said, I want to be mindful that we don't get too distracted by things in the amp circuit when our main issue seems to be at the input transformer. These measurements that I'm asking him to do throughout the circuit are not so much to determine exact impedances but rather suss out any shorts to ground that might be hiding in there.

____

As I said earlier, based on what we've tested already over the last couple pages, I can only see one reason that there would be no signal on R0, and that is if there is a short to ground in the audio path somewhere. Otherwise, even if there are cold solder joints or burned out components or even cut traces elsewhere in the circuit, I can't come up with a reason why you wouldn't have signal on the right leg of R0. I know we have already verified the connections around the input transformer to death, but can you - in addition to answering the questions above - power the unit up, send your test tone again, and measure AC signal between [pins 2 & 5] and [pins 7 & 10] directly on the transformer (not on the J1 connector but the transformer pins themselves)?

 

[capacitorless]

I would say that this effort is helping me with my own troubleshooting (I mean in general), and very likely other people reading through it as well. Very cool to see the level of support you're providing to everyone.

I don't have one up and running yet, but I'm pretty stoked to find out how good it sounds.

 

[Forcemusicgroup]

Can you be more specific? I mean, are we talking about a slow steady creep of a few ohms, or are we talking about quickly jumping around in large leaps from hundreds of ohms to thousands and back again? (Or something different?) And how long are you watching the meter drift before you remove the probe? It sounds to me like a capacitor is charging from the small current that your multimeter is providing but "drift" is not precise enough to be sure we're understanding the same thing.

Did you redo the continuity tests with the module removed from power?


Please feel free to get in the way! I think Forcemusicgroup is a relative beginner (no judgement, we all start as beginners) and isn't sure how to go looking for problem spots on his own, so any thoughts on what might be going on are welcome as we try to find the issue.

That said, I want to be mindful that we don't get too distracted by things in the amp circuit when our main issue seems to be at the input transformer. These measurements that I'm asking him to do throughout the circuit are not so much to determine exact impedances but rather suss out any shorts to ground that might be hiding in there.

____

As I said earlier, based on what we've tested already over the last couple pages, I can only see one reason that there would be no signal on R0, and that is if there is a short to ground in the audio path somewhere. Otherwise, even if there are cold solder joints or burned out components or even cut traces elsewhere in the circuit, I can't come up with a reason why you wouldn't have signal on the right leg of R0. I know we have already verified the connections around the input transformer to death, but can you - in addition to answering the questions above - power the unit up, send your test tone again, and measure AC signal between [pins 2 & 5] and [pins 7 & 10] directly on the transformer (not on the J1 connector but the transformer pins themselves)?

Okay, let's start broad and narrow it down from there. I am going to ask you to report back in as much detail as you can, please.

Send a 1k test tone to the unit.

With your multimeter in AC mode, confirm that you have a healthy signal between IN+ (red probe) and IN- (black probe) on the edge connector. Actually it does not matter which probe goes to which pin, but you should measure AC voltage here. I would suggest adjusting the level of the test tone until you read something like ~1.228VAC across those pins, or 0VU. The level will drop considerably as we work our way through the passive circuit, then should increase back up to unity gain as we go through the amplifier section. But it should never disappear completely.

Set your front panel controls to twelve o'clock (no gain). With your meter still set to measure AC voltage, place your black probe on the Aud GND pin of the edge connector, then use your red probe to measure the following points relative to Aud GND:

-Both sides of R0
-the bottom leg of R11
-the top leg of R25
-Both sides of R27
-Both sides of R28
-the right leg of R29

Then measure the AC voltage between Out+ and Out- on the edge connector.

Since your unit is not passing signal, you should see it drop out somewhere in that sequence.

Again, please report back with specifics.

- large leaps from hundreds of ohms to thousands and back again, I can hold my meter there forever and it will drift from about 50ohms up to 568k ohms back down again.. then reset. Continuing cycle

Im just checking for continuity here, without power

-Both sides of R0 - no connection
-the bottom leg of R11- no connection
-the top leg of R25 - nothing
-Both sides of R27 - nothing
-Both sides of R28 - nothing
-the right leg of R29 - nothing

AC signal between [pins 2 & 5 =0 vac] and [pins 7 & 10 = 0 vac] directly on the transformer (not on the J1 connector but the transformer pins themselves.....)


-Both sides of R0 - 0 vac on both legs
-the bottom leg of R11 - 0 vac
-the top leg of R25 - 0 vac
-Both sides of R27 - 0 vac
-Both sides of R28 - 0
-the right leg of R29 - 0 vac

 

[capacitorless]

0vac across both the primary and secondary of the input transformer: it seems like might be a relay issue. I missed if any of this has been mentioned already (apologies if so). Focusing on both of the relays here:

Is VR1 adjusted correctly? I think so but asking to be certain

If there's no signal applied to In+ and In-, continuity measurements on the input relay K1 are valid, when the unit is powered up:

Apply power, switch the unit in (meaning where it should be processing/eqing the signal), and check continuity between In+ and pin 8 on K1, and then check continuity between In+ and pin 2 on T1.

If you wish you can repeat the same test between In- and pin 9 on K1, and In- and pin 5 on T1.

While the unit is in the same state, check continuity between Out+ and pin 9 on K2, and again between Out+ and pin 4 on T2.

Edit: apologies again if this has been conclusively tested already. I'm unclear on whether this was done to completion.

 

[Forcemusicgroup]

0vac across both the primary and secondary of the input transformer: it seems like might be a relay issue. I missed if any of this has been mentioned already (apologies if so). Focusing on both of the relays here:

Is VR1 adjusted correctly? I think so but asking to be certain

If there's no signal applied to In+ and In-, continuity measurements on the input relay K1 are valid, when the unit is powered up:

Apply power, switch the unit in (meaning where it should be processing/eqing the signal), and check continuity between In+ and pin 8 on K1, and then check continuity between In+ and pin 2 on T1.

If you wish you can repeat the same test between In- and pin 9 on K1, and In- and pin 5 on T1.

While the unit is in the same state, check continuity between Out+ and pin 9 on K2, and again between Out+ and pin 4 on T2.

Edit: apologies again if this has been conclusively tested already. I'm unclear on whether this was done to completion.

VR1 adjusted = 24 vdc
pin 8 on K1 - there is a complete circuit with voltage
In+ and pin 2 on T1 - no continuity

In- and pin 5 on T1 no continuity

In- and pin 9 on K1 = continuity
Out+ and pin 9 on K2= nothing
between Out+ and pin 4 on T2. nothing