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

SunkenCity said:

both connectors cn4 and cn5 are junk after heating  them enough to get all the leads free, hot pins just warp the plastic. 

By force I mean I snipped the leads I could access and removed solder where I could with wick to get it free to access the pads for the connectors.

CR1 tested fine but I might as well replace it with the one you sent.

Not sure where to go from here.  It would be a waste of time to stick the replacement trannys in if the problem is somewhere else. I guess recheck everything in the line amp section

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SunkenCity said:

rechecked every component in the line amp section with another set of eyes, everything is correctly populated.

Does that mean it had to have been Q5?

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Hairball Audio said:

It's impossible to say.  Troubleshooting electronics is a hands on practice. Mostly, I just make educated guesses based on what you are telling me. I've not seen your soldering, or probed anything myself. It's like asking me how to fix a mix without actually hearing the mix.

If removing Q5 correctly your rail voltage, then either Q5 has shorted or you have a misplaced component, bald solder joint, or lifted pad between Q5 and the 30VDC rail.  Keep in mind many of our repairs come down to lifted pads. Q5 and CR1 being shorted would certainly draw a lot of current and would be where I would start.  Also confirm continuity between components in that line amp section.

Mike

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SunkenCity said:

I solder stuff for an aerospace company all j-std stuff but I guess there's always room for error , I'm using a Metcal unit where the tip controls the heat. The tip I'm using sets the temp to 775f, Is it possible this is too much for the tranny even if I'm flowing it very quick?

I started doing a continuity test working off the schematic and it seems like everything is connected that should be. Would be good to know where there should not be continuity.

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Nao_Idea said:

Hello,
I am building a Rev F.  I have completed the Power Supply.  I did the testing.  The Ground measured 0.2 ohms, the same value when I touch the leads together. 
CR8: 32.2 V DC
CR9: -9.7 V DC

Note: CR8 voltage does increase steadily over a short period of time.  But even from pressing GR to power it on, it is above 31.5V DC 

Thanks,
Mike

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aste said:

Hi, all,

I just finished the build and haven't gotten to calibration, or an audio test yet; just letting it burn in for a while and make sure it doesn't blow up, or anything.

Anyway, is it normal for the Rev A to be really warm to the touch. I mean, it's hot, but you can leave your hand on it without discomfort.

Also, is it normal to hear a hum coming from it if you place your ear close?

Thanks,
Andrew

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Hairball Audio said:

Q6 is going to get hot.  Anything else hot?  If your fuse didn’t blow that’s a good sign.  Are your rail voltages fine?

They fuse is there to keep anything catastrophic from happening.

Mike

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Hairball Audio said:

775F is a little high but not high enough for it to be an issue with decent technique.

Schematic will show you where continuity should be.

Did you try the new transistor?

Mike

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Hairball Audio said:

Are you concerned about the voltages?  They +/- 10%.  Looks good to me.

Mike

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aste said:

Yeah, I read that Q6 was going to be hot. I guess it could be heating the whole unit. I haven't opened it up again, so don't know for sure, but maybe the power transformer is adding a little heat too? I will pull the lid off tomorrow (it's at work) and have a check around.

I was pretty happy when I fired it up and nothing popped, or caught on fire, just want to make sure the hottish/warmth is normal.

As for the rails, assuming you are talking about the power supply voltages; when I tested them after building the power supply, everything was within spec. I'm only assuming that nothing has changed, in that respect, since.

Anyway, thanks, Mike, for the reassurance. As soon as I can get a 1khz signal injected, I will go through the calibration process and see where I'm at with the rest of it.

Thanks again!
Andrew

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SunkenCity said:

Yeah I tried putting another in, same voltage drop down to 20 vdc. Had all the ESD stuff like I did for the whole build(bracelet, mat, tools and gloves.) For the trannys I put some solder on the tip(instead of heating the joint and feeding in solder), hit the joint for 1(Mississippi) second then waited a minute or so to re-flow the joints for a second each.

Last time I was doing the continuity test I was getting resistance readings everywhere but ended up getting a little lost in the schem. I'll go thru it again, this time marking down where I'm at and what I've done so far by the numbers

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Nao_Idea said:

I was concerned because the build guide specs +/- 5%. 
Is the increase normal? 
My voltage at CR5 is reading 31.4v dc as soon as I hit GR for power.  The voltage increases slowly but steadily to 32.7v dc (it might go higher but I shut the unit down).

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Hairball Audio said:

You may want to test the D1 diode and look for shorted caps around that transistor.  It's gotta be right around there.

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SunkenCity said:

Just did a continuity test from every component lead to what they are supposed to be connected to and everything is connected thru the pcb properly  no broken traces or joints. 

By shorted do you mean no resistance from one lead to the other on a cap? 

I tested the diode before I replaced the original.  What would a bad diode test like while in the circuit?

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