[BUILD] New FET/RACK Official Help Thread - Please read first post!

[Echo North]

Haven't put a Q4 back in yet. output xformer is wired up right. I replaced cr1 with one you sent.

I noticed when I put the meter (in the resistance setting) across c9 the meter doesn't settle on anything and jumps around from overload to random readings.

It's interacting with the rest of the circuit. Could bounce around forever.

 

[SunkenCity]

Ill pull Q6 and test it

 

[SunkenCity]

pulled and tested Q6 and it isn't shorted or open.

 

[scott2000]

I noticed when I put the meter (in the resistance setting) across c9 the meter doesn't settle on anything and jumps around from overload to random readings.

Do you have a way to test it besides a dmm?or  maybe you could pull it and test it???

 

[SunkenCity]

Do you have a way to test it besides a dmm?or  maybe you could pull it and test it???

my fluke has a capacitance tester setting if I do pull it out. 

 

[Nao_Idea]

A little increase would be normal.  If it keeps getting higher that can be an issue.  How long are you keeping it on?

Keep in mind sometime higher or lower voltages can be related to the test equipment.

Mike

(Keep in mind I was looking at these voltages initially with the  understanding that it should be within 5% of 30 v DC)

To answer your question of how long am I keeping on, I did a little test.  All volts are DC. 

Power on voltage was 31.5.
1 min: 32.0
2 min: 32.3
3 min: 32.4
4 min: 32.5
At 11 minutes it went to 32.6 and stayed there until sometime after 20 minutes.
I walked away from it for a while, at 38 minutes it was steady at 32.5 v DC. 

I realize that meters can vary in accuracy.  I happen to be using a Fluke 87 V DMM which is calibrated for work, so I trust these values.   

Thanks for your help Mike. 

 

[Echo North]

(Keep in mind I was looking at these voltages initially with the  understanding that it should be within 5% of 30 v DC)

To answer your question of how long am I keeping on, I did a little test.  All volts are DC. 

Power on voltage was 31.5.
1 min: 32.0
2 min: 32.3
3 min: 32.4
4 min: 32.5
At 11 minutes it went to 32.6 and stayed there until sometime after 20 minutes.
I walked away from it for a while, at 38 minutes it was steady at 32.5 v DC. 

I realize that meters can vary in accuracy.  I happen to be using a Fluke 87 V DMM which is calibrated for work, so I trust these values.   

Thanks for your help Mike.

Ya I just think there is something else going on, I wouldn't worry about it.  You try a new voltage regulator or transformer, but I would stuff the rest of the PCB first and see what you're getting.

 

[SunkenCity]

Q6 tested fine what should I look at next?

 

[Echo North]

Q6 tested fine what should I look at next?

Damn, not sure what to tell you at this point. Something in your line-amp is is causing your voltage rail to drop. Bad solder joint, fried component, something.  There isn't much left to test short of pulling every component in that section and testing it.

If you have another kit you could try a different output transformer, but I'd be pretty surprised if that was the issue. Not out of the question however.

You can always send it in and we'll figure it out.  Honestly, I'd probably just re-stuff the line amp. There has to be a ghost in there.

Mike

 

[SunkenCity]

Is there a way to test the output xformer with it in the circuit or out if need be?

On the pcb is the ground plane surrounding all the solder pads? like if the coating was scratched off surrounding a solder pad is it possible there could be a solder bridge cause a short?

Also before stuffing some of the orange caps I noticed they arrived with small fractures where the leads come out of the component. Normally with j-std stuff we have to reject components like that but I thought it was just really high manufacturing standards. Is that a possible problem?

You said the C9 reading was normal right? Or should I pull it and test it.

I put the meter across all the caps in the line amp section while in the circuit and most climbed up(or down) towards infinity a few had solid readings maybe its a hint at something so I'll list em:
c14 = 40.3 ohms
c13= 3.802 k
c16 = 0.738  k

I put the meter on the replaced CR1 one again with it soldered in and it's reading slowly increasing resistance in both directions. Is that normal when its in the circuit? I thought I would only get a measurement in one direction.

 

[Echo North]

Is there a way to test the output xformer with it in the circuit or out if need be?

Not really. There is so much parallel R/C you'd be calculating for days.  Even if you pulled it all you could do is check for shorts or breaks across the windings. Which can be helpful.  Keep in mind on those outputs at most 1 in 1000 are bad.

On the pcb is the ground plane surrounding all the solder pads? like if the coating was scratched off surrounding a solder pad is it possible there could be a solder bridge cause a short?

No scratched solder mask/exposed traces wouldn't cause a bridge or issues like this.

Also before stuffing some of the orange caps I noticed they arrived with small fractures where the leads come out of the component. Normally with j-std stuff we have to reject components like that but I thought it was just really high manufacturing standards. Is that a possible problem?

No.  Even if they were defective, they are AC coupling caps that would kill your AC signal not change your DC readings.

You said the C9 reading was normal right? Or should I pull it and test it.

You could, not sure it would cause the issue you're seeing though. At some poind if you pull enough stuff, your risk damaging pads and traces.  That is fixable. But be careful.

I put the meter on the replaced CR1 one again with it soldered in and it's reading slowly increasing resistance in both directions. Is that normal when its in the circuit? I thought I would only get a measurement in one direction.

Again, you have caps in parallel. So that sounds normal in circuit.

Sorry I don't have anything else for you.  I just need to look at it for a while. Keep in mind if it was a bad output transformer or defective PCB (which I have never seen in 12 years), you would not be charged.

Mike

 

[SunkenCity]

there's gotta be something to put the meter on to figure out what's wrong on this thing, right?

I'm getting 24. k resistance from the tip of the rca to chassis. Also there is a strange milky looking build up on the pcb around the rca tip's solder joint. I'm sure I cleaned it with iso and a wipe.

 

[scott2000]

there's gotta be something to put the meter on to figure out what's wrong on this thing, right?

I'm getting 24. k resistance from the tip of the rca to chassis. Also there is a strange milky looking build up on the pcb around the rca tip's solder joint. I'm sure I cleaned it with iso and a wipe.

I tried back tracking through your problem but it's hard to determine what could've happened. It's clear that something happened but, without knowing, it seems you may want to check as many components as you can.

Unit one is shorting out at the cn4 connector lighting it up

Disconnected all connectors from the meter pcb except c4 plugged it back in and it shorts and sparks immediately.

Swapped the meter board assembly with the other unit and it didn't spark attempted cal with no luck still no output at the xlr. Checked cr8 and cr9  got about 20.00 vdc and 9.70 vdc checked the other unit after putting it back together and got the same readings.  looked at cr8 on both units and it looks like it bubbled out a bit.

Sparks and bubbled components are never a good thing...

I use a cheap LCR meter and they are pretty good for checking caps and resistors in circuit and it's surprisingly good .... That, along with a DMM for checking diodes and transistors, you could scan through everything in very short time..... If a reading is goofy, then you can pull a component to check if the circuit is causing the goofy reading or not....

Maybe your meter is good enough since it has a capacitance meter but I wouldn't know....What kind of meter to you have????

Discharging the caps is always a good idea before you start checking too......

of course check everything with power off...I'm not talking about testing voltages......just component values and looking for problems

 

[SunkenCity]

The unit(unit 1) that was sparking at the off switch isn't the one i'm trying to troubleshoot now but I wasn't getting proper voltage on that unit either when I switched out the off switch with the other unit.  I set unit 1 aside until I get some replacements from mike.

both units were producing proper voltage after the power supply was assembled

I went and got the recommended fluke 117.

 

[Echo North]

The unit(unit 1) that was sparking at the off switch isn't the one i'm trying to troubleshoot now but I wasn't getting proper voltage on that unit either when I switched out the off switch with the other unit.  I set unit 1 aside until I get some replacements from mike.

both units were producing proper voltage after the power supply was assembled

I went and got the recommended fluke 117.

Unfortunately, there is only so much I can do over the forum.  I can't relay 12 years of troubleshooting these units beyond what I have done which is locate where *I think* the issue might be having not held the unit myself.

$150 repair is a crazy good deal.  It's like your car catching fire and a mechanic saying he'll fix it for $150 flate rate.  I may end up spending 3-5 hours on the unit.  Also, if you have a bad transformer (not likely, but possible) it's free. You may want to consider saving yourself hours of headache and just send in the boards.

If you want to keep working on it, I'm happy to answer any questions you have here. You can see looking through the thread I can usually help people get them working on here, but at some point even I get stumped and tap out. Some issues are super weird and even the clues mislead me.

Good luck!

Mike

PS: last thought, try swapping the power transformers on the unit.

 

[SunkenCity]

In 12 years you've never run into a similar problem where putting Q5 in the circuit causes the voltage drop?

Is there a procedure for going thru it with an audio probe with those resistors, Q4,  and Q5 out of the circuit?

Would running a signal thru the output xformer tell you anything?

 

[Echo North]

In 12 years you've never run into a similar problem where putting Q5 in the circuit causes the voltage drop?

Nothing specific to Q5.  Have seen voltage drops after stuffing from a shorted component.

Is there a procedure for going thru it with an audio probe with those resistors, Q4,  and Q5 out of the circuit?

Like I've said. Test everything in your output amp. However, at this point I can guarantee your issue i there, only an educated guess.

Would running a signal thru the output xformer tell you anything?

Not really, there is a lot more than signal going through the output.

You have a pretty advanced issue and I'm stumped.  I'd have to look at it.  Trust me I hate doing repairs, we make no money doing it and they take for ever even when they're easy with all the set up and strip down. I'd rather sort it here.  I'm just stumped at this point.

Mike

 

[SunkenCity]

all the resistors are the correct color code. I put a meter lead to lead on all the resistors in the line amp section while in the circuit. maybe these hint at something?

r28 = 521.8 ohm

233 = 557.7 ohm

r31 = 3.26k

r35 = 8.15k

r34 = 0.738k

r27 = ??? flickered and never settled on a valve

r26 = 32.89k

r30 = 150k

r29 = 222.9m

r7 = 2.19m

r25 = 2.59m

R24 = 2.65m

 

[Echo North]

all the resistors are the correct color code. I put a meter lead to lead on all the resistors in the line amp section while in the circuit. maybe these hint at something?

r28 = 521.8 ohm

233 = 557.7 ohm

r31 = 3.26k

r35 = 8.15k

r34 = 0.738k

r27 = ??? flickered and never settled on a valve

r26 = 32.89k

r30 = 150k

r29 = 222.9m

r7 = 2.19m

r25 = 2.59m

R24 = 2.65m

Again, in circuit everything is interacting. You need to lift leg.

 

[SunkenCity]

Isn't that what we wanna know how things are interacting?

majority of those readings are more or less spot on with the valve of the resistor, there is only a few that aren't their stock value.