[BUILD] FET/500 Official Support Thread

[stevelawaudio]

Hi All -

I've done some more testing and found the following..

If i drop the output control down, to around +5dBu i can adjust the LEDs up and down the meter.
When I set the output back to +16dBu, I have no movement in either direction up or down.


s.

 

[jcohen]

Hello! I've just finished my first FET500 Rev A build. Everything went great and seemed to be in order until calibration time. When I went to calibrate the unit, the qbias didn't seem to be making a difference (turning either way would alternate my multimeter from 0.016 to 0.017 VAC). Also putting my output to full still only yielded me at most about 0.800 VAC whereas the video was showing more that 2 VAC. All my reading seemed to be low, then about 10 minutes in, I heard a nice frightening POP. Immediately turned the unit off and removed it to find that the 100 uF 50V cap in C4 spot had blown it top up a bit. Don't want to plug the unit back in until I can diagnose what would do such a thing. Any ideas what might have gone wrong? I did a full look over and don't see any parts installed other than instructed by schematic. Below is a picture of the C4 cap that has blown.

 

[Echo North]

Hey Mike -

just been across it with a DMM - found a few values that are correct in colour banding but are reading a bit low.
examples -
R207 (100k) is reading 72k
R216, R213, R215 (100k) are reading 80k
R227 (10k) is 5.3k...etc..
there are a few more reading low too..

thanks for your help!

S.

You can't really measure resistors in circuit without lifting a leg or understanding the math of parallel resistance.  Many will read low as they are now in parallel with other resistors.

Mike

 

[Echo North]

Hey Mike -

Yep, got signal in and out, and the LEDS are lighting. They just won't move with the trim pots. Turned the trims fully each way, and no luck/movement.

thanks mate!

S.

Do you have the right value trimmers in the correct spots?

 

[stevelawaudio]

You can't really measure resistors in circuit without lifting a leg or understanding the math of parallel resistance.  Many will read low as they are now in parallel with other resistors.

Mike

Ok. Thought it would be something like that.

Do you have the right value trimmers in the correct spots?

Yeah, 10k at VR1 and 1k at VR2.

Any ideas of why it works at a lower voltage?

Thanks.!
S.

 

[Echo North]

Ok. Thought it would be something like that.

Yeah, 10k at VR1 and 1k at VR2.

Any ideas of why it works at a lower voltage?

Thanks.!
S.

Are the all illuminated at higher v?

 

[stevelawaudio]

Are the all illuminated at higher v?

As i increase the output each LED lights up as it goes up.
Then when it hits around +6 it gets to the LED209 and stays there. I can't get Peak (LED210) to light.

Then as I wind up the output to +16, the 209 LED stays lit, and the trim doesn't change anything.

I drop the output to around +2 and then i can adjust the LEDs 2 or 3 LEDs.

Can i email you a little video.?

Thanks Mike!

Steve.

 

[Echo North]

As i increase the output each LED lights up as it goes up.
Then when it hits around +6 it gets to the LED209 and stays there. I can't get Peak (LED210) to light.

Then as I wind up the output to +16, the 209 LED stays lit, and the trim doesn't change anything.

I drop the output to around +2 and then i can adjust the LEDs 2 or 3 LEDs.

Can i email you a little video.?

Thanks Mike!

Steve.

I don't think a video would help.

Really it comes down to:

1. Misplaced component
2. Damaged component
3. Bad solder joint
4. Damaged pad/trace
5. Backwards/unsoldered LEDs - wiggle the LEDs make sure both legs are connected.

Go through all they and report back.

Does the GR metering work?

Mike

 

[Catrunes]

Hi all, one of the 2 rev D fet 500 kits I built will not reduce gain more than 1-2 db no matter what i do to it. The other unit I built works perfectly as intended. There is one thing you should know though, when i first built faulty unit, i had reversed one of the power filtering electros and i had to replace it, is there any chance i blew a fet or something? any help is appreciated. thank you max

 

[Echo North]

Hi all, one of the 2 rev D fet 500 kits I built will not reduce gain more than 1-2 db no matter what i do to it. The other unit I built works perfectly as intended. There is one thing you should know though, when i first built faulty unit, i had reversed one of the power filtering electros and i had to replace it, is there any chance i blew a fet or something? any help is appreciated. thank you max

Probably a GR Amp issue.  Is the over all gain (in GR OFF) the same as the other one?

 

[Catrunes]

Yes it acts the same as the functional unit in gr off mode. Gain seems fine

 

[Echo North]

Yes it acts the same as the functional unit in gr off mode. Gain seems fine

I would check everything in your GR Amp section (vertical resistors back corner) and resistors by your grayhill switch.

Calibration went fine?

Mike

 

[mdmitch2]

I'm trying to figure out why the gain reduction on/off LED isn't working.... I've built probably 8 of these, and this is the first time I've encountered this issue.

Basically, when I first built the unit (rev D), everything worked fine except the LED didn't turn on when I engaged the switch. However, the switch worked as you would expect, just no light from the LED. I checked that it was in the correct orientation, and also checked it with my multimeter, and just for good measure, swapped it with one of the meter LEDs. When I re-assembled, it still would not light up (and the swapped meter LED was fine). So I proceeded to verify all component values, diode/cap orientation, etc, and everything was correct. Then I reflowed the LED and switches, as well as the relays and ICs, and put it back together.... BINGO it worked as expected, and I was able to calibrate the unit with no issue. THEN, the next day, I powered it up, and no light from the LED again..... everything else works/sounds great.  Any ideas?

Thanks!

 

[Echo North]

I'm trying to figure out why the gain reduction on/off LED isn't working.... I've built probably 8 of these, and this is the first time I've encountered this issue.

Basically, when I first built the unit (rev D), everything worked fine except the LED didn't turn on when I engaged the switch. However, the switch worked as you would expect, just no light from the LED. I checked that it was in the correct orientation, and also checked it with my multimeter, and just for good measure, swapped it with one of the meter LEDs. When I re-assembled, it still would not light up (and the swapped meter LED was fine). So I proceeded to verify all component values, diode/cap orientation, etc, and everything was correct. Then I reflowed the LED and switches, as well as the relays and ICs, and put it back together.... BINGO it worked as expected, and I was able to calibrate the unit with no issue. THEN, the next day, I powered it up, and no light from the LED again..... everything else works/sounds great.  Any ideas?

Thanks!

That LED is just a two component circuit.  The LED, R510 and the switch.  I would check for continuity between those three components.  Could be a slightly lifted pad, or even that pole of the switch is weird.

 

[mdmitch2]

That LED is just a two component circuit.  The LED, R510 and the switch.  I would check for continuity between those three components.  Could be a slightly lifted pad, or even that pole of the switch is weird.

Thanks -- that's what I was thinking.... so it seems like a faulty switch is the most likely culprit at this point. Is there a way to test the switch in circuit? I checked continuity between the switch and R510 (see pic), and when the switch is disengaged, I get continuity between the green circled points, and when it's engaged, there is also continuity with the red circled point, and no others.

 

[Echo North]

When the button is pushed in, only these should have continuity.

 

[Echo North]

When the button is out, only these should have continuity.

 

[mdmitch2]

When the button is out, only these should have continuity.

The two areas that you circled in blue -- should those have continuity with each other? i.e. between all four points in blue? Mine do not.... but I noticed that all four have continuity on the red led bypass switch.

 

[Echo North]

The two areas that you circled in blue -- should those have continuity with each other? i.e. between all four points in blue? Mine do not.... but I noticed that all four have continuity on the red led bypass switch.

Not all 4 points.  Just the two circled. There are 2 separate switches on the switch. They have no relation to each other.

Google DPDT. One switch is the 3 terminals on one side, one switch is the three terminals on the other side. The middle terminal on each side is the common.

 

[Echo North]

Look at the gif on the left and imagine that is you pushing the switch in and out.

http://www.zseries.in/electronics%20lab/switches/slide/pictures/working%20of%20dpdt%20slide%20switch.gif

The two sides are isolated.