[utilisateur]

I'm resurrecting my β22 boards and have some setup problems
I bet the answers are already somewhere in the headwize thread but headwize is down

So when i try to do the initial setup i cant adjust the Voltage across R9, VR1 makes minimal changes i have 1,3V across R9 with VR1 turned fully ccw and 1,8V with VR1 fully CW



maybe someone has a clue or plain knows what is wrong or what i should check to find out
I'd really appreciate your help !

 

[MrMajestic2]

Quote:

Originally Posted by utilisateur /img/forum/go_quote.gif I'm resurrecting my β22 boards and have some setup problems I bet the answers are already somewhere in the headwize thread but headwize is down So when i try to do the initial setup i cant adjust the Voltage across R9, VR1 makes minimal changes i have 1,3V across R9 with VR1 turned fully ccw and 1,8V with VR1 fully CW maybe someone has a clue or plain knows what is wrong or what i should check to find out I'd really appreciate your help !

Are you sure you have the right VR in the right location? I remember I mixed mine up the first time since they are not in order on the board.

 

[utilisateur]

Thanks
I quadruple checked as that had happened twice before, and just rechecked , they are definitely in the right order and connections are good

 

[Bojamijams]

bought most parts.. waiting for them to arrive...

 

[paaj]

Just ordered the GJA kit (I'm not really into the whole DIY gathering stuff thing

) and see how far I can get without blowing all up.

 

[utilisateur]

Quote:

Originally Posted by paaj Just ordered the GJA kit (I'm not really into the whole DIY gathering stuff thing ) and see how far I can get without blowing all up.

Jeffs Kit really is very convenient!

Quote:

Originally Posted by utilisateur [size=xx-small]So when i try to do the initial setup i cant adjust the Voltage across R9, VR1 makes minimal changes i have 1,3V across R9 with VR1 turned fully ccw and 1,8V with VR1 fully CW maybe someone has a clue or plain knows what is wrong or what i should check to find out I'd really appreciate your help ![/size]

On another board VR1 works fine and i pass that step but i have a discrepancy between R34 and R35
Only 5mV to ground from R34/Q21source OpPoints PDF says 80,52mV
And 1,4V to ground from R35/Q22source -80,58mV

maybe something around Q17/18?
the meter reads
-430mV to ground from the Q17/18 emitter junction 175,4mV
-1,1V at Q18 Base -601,7mV
238mV at Q17 Base 900,3mV

Ideas?

 

[Gatsu]

Not long ago finished putting together my two Sigma22's.

First one worked first time, second one I discovered I had gotten the 4 of the transistors swapped around. Only to blow up another transistor fixing those. /facepalm

Once I sorted that out all worked. Haven't started on assembling the Beta boards yet. I've been working on the controller boards.
My build is heavily influenced by naamanf's infamous build

2 picaxe microcontrollers (one in each case) control power and power status indication (S22 case) as well as input/output selection and indication (B22 case), as well as a Joshua Tree attenuator.

Its certainly been a learning experience so far

 

[FallenAngel]

Quote:

Originally Posted by utilisateur /img/forum/go_quote.gif Jeffs Kit really is very convenient!

And makes it that much easier for people to take on projects they don't know how to debug.

Quote:

Originally Posted by utilisateur /img/forum/go_quote.gif Ideas?

Double and triple check that you did not swap the 5K and 500R trimpots.
Take high quality photos of the top/bottom of the board and post.

 

[utilisateur]

Quote:

Originally Posted by FallenAngel Quote: Originally Posted by utilisateur View Post Jeffs Kit really is very convenient! And makes it that much easier for people to take on projects they don't know how to debug.

Quite true ..
Personally i only attempted seeing it as a great learning opportunity and counting on the enormous knowledge available trough the internet and especially forums like headwize (and this thread).
Assuming this wasn't available i would have tried to find knowledgeable people willing to share and teach around the place i live but the net makes such knowedge available far more easily and maybe makes it harder to find it locally (?) as people dont form clubs or whatever but go talk and exchange experience trough the web.



[size=xx-small]Photos to follow in an [/size]edit! = )

board 1 where VR1 works but R34/R35 doesnt behave


board 2 where VR1 had no effect



more

 

[amb]

Check the voltage (relative to ground) at the outer pin of R9. If you don't have around 27-20V or so, then your Q25 is blown. Ditto at the outer pin of R11, you should get -27-29V. If not, then Q26 is blown.

Make sure your Q1-Q4 are mounted according to the "instructions" section of the β22 website (not according to the silkscreen).

 

[utilisateur]

I measure 28,2V/-28,2V on both boards and Q1-4 are soldered according to the information on your website!

Can i check the small signal transistors in circuit, except checking for shorts(there are none)?

Can you read anything explicit from the measurements?
These were those that were the most suspicious to me
Quote:

On another board VR1 works fine and i pass that step but i have a discrepancy between R34 and R35 Only 5mV to ground from R34/Q21source OpPoints PDF says 80,52mV And 1,4V to ground from R35/Q22source -80,58mV maybe something around Q17/18? the meter reads -430mV to ground from the Q17/18 emitter junction 175,4mV -1,1V at Q18 Base -601,7mV 238mV at Q17 Base 900,3mV

 

[amb]

Yes, you can test the BJTs. Power off and let all caps discharge fully. Then, set your DMM to the diode check mode. For NPN transistors (BC550C), put the red probe on the B pin and the black probe on the C and E pins. You should read about 0.6V on both. Reverse the probes and you should read infinity (depending on your DMM it would display either "OL" or "1"). For PNP transistors (BC560C), it's just the opposite. Black probe on B and red probe on C or E = 0.6V, reverse probes and you should get infinity.

Any transistor that fails this test on the β22 board is most assuredly blown.

Note that this test does not apply to JFETs or MOSFETs.

For your other board, the initial setup procedure is to measure the voltage across R34 and R35, not relative to ground. Your observed discrepancy simply means that the output DC offset has not been nulled yet.

 

[utilisateur]

Quote:

Originally Posted by amb Yes, you can test the BJTs.

Thanks i will test them
Now a substantial amount of the BJTs measures around 1,5 or 1,8 in the reverse direction and some fluctuate slightly before my meter settles above the range..
[size=xx-small]In diode check mode my meter reads 1 when the forward voltage is higher than 2V[/size]
Assuming they are dead, what could have caused this ? I don`t think i was this heedless when soldering them but always trying not to heat them too long


Quote:

For your other board, the initial setup procedure is to measure the voltage across R34 and R35, not relative to ground. Your observed discrepancy simply means that the output DC offset has not been nulled yet.

I think i did measure across the resistors but the change across R34 was not large enough, just posted the values relative to ground in case this could hint to a fault!
I hope my mind doesn't fool me on this or better i hope it did, anyhow i go and check again!
thank you!
So i just checked and i cannot adjust the voltage across R34 at all it sits quietly at 0,0V
When i measure R35 on the other hand with the pot fully closed i get 1,13V across it and it climbs when VR2 is changed
I did not turn VR2 fully clockwise as i didnt want to raise the voltage across R35 further , four turns it it's at 1,5V and R34 still at 0,0V

 

[utilisateur]

I cant see how most of the BJT on both my boards could be dead

To make sure the replacements do well, what else can i check ,considering they are not dead short but fail the reverse test as described above ?

Wow, after trying to get a better understanding of the schematic i went ahead to check some points on the board and checked R34 R35 while doing so and
R35 measured 51kΩ
It' marked with a 0,47Ω color code !
Weird stuff

HEUREKA

I got both boards through the initial setup procedure =)

I still wonder what i should do with the BJTs measuring slightly lower than amb recommended,
in what way are they detrimental to the circuits properties ?

Also on the board i had the wrong/damaged resistor in position R35 the voltage across r35 is 20mV lower than across r34 ,has this happened to anyone or does someone know what could cause this?


Having to look for the solution myself I definitely learned more, and i'm happy i now have a better understanding about what's happening on this green miracle that makes sound mo' big and transducers sing .)

 

[utilisateur]

What consequences are there from the 20mV difference between R34 and R35?
And what could cause this behaviour?

Q17/18 are not the culprit i replaced them and it did not change anything

As said there are no immediate audible effects.. i would like to know whats going on there as the amp is changing hands and i dont want to hand down this issue