Q28 burning & after a while R151 burns [SOLVED- PCB ERROR]]

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Q28 burning & after a while R151 burns [SOLVED- PCB ERROR]]

Postby p4rancesc0 » Jul 27th, '14, 19:44

Hi, I've got a problem with the HC/MC section:

after soldering everything (voltages on BA were ok) I connected:

1) 5V 1ms trigger to r105
2) +5V form the yocto psu to R103 (this worked for all the other instruments testing)
3) r296 to the audio speaker

in few seconds q28 got really hot (just after i connect the accent R103) and burned.

I replaced it with a spare one with lower hfe (the first was 350, the second 335).

I did a second run and it worked for few seconds (I could hear the HC), but then it became really hot and I disconnected everything.

I think now it's fried again bacause on the third test I could hear anything.

I went back to rimshot and there (with the same procedure) is still working fine.

I tried to attach the trigger directly to r350 (I could hear something like an handclap), to the collector of Q69 (I could hear something like an handclap) and to the collector of Q67 (I could hear something like a maracas).

It seems that the problem is located in the circuit before the switch (q28/q29 and those 4 resistors).

Any idea ?
Last edited by p4rancesc0 on Aug 2nd, '14, 16:25, edited 2 times in total.
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Re: Q28 burning

Postby p4rancesc0 » Jul 27th, '14, 19:52

sorry for double posting...
can anyone please post a mouser code for 2sc945 and the 2sa733 ?
Thanks !! :D
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Re: Q28 burning

Postby gihaume » Jul 28th, '14, 09:18

p4rancesc0 wrote:in few seconds q28 got really hot (just after i connect the accent R103) and burned.

A few people including me did have a problem with the CD4011 (accent circuit) of the last batch and have to change it for a new one: TI CD4011 BE for me. I did not look at where is the q28 but it's an idea I just had in reading that the issue appeared just after you connected the accent circuit.
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Re: Q28 burning & after a while R151 burns

Postby p4rancesc0 » Jul 28th, '14, 19:42

thanks for the hint.

I really thought that there was no correlation between the r151 and the HC issue, but today, after checking everything and substituting q28 and q 29 my issues was still there.

Q 28 gets really hot after 2 seconds i connect the +5V from the psu to r103. Today i just managed not to burn q28 by disconnecting the +5V in time .
I checked the resistance between q28 base and ground, between r103 accent input and ground and they looks fine to me (about 10K orders not 10 Ohm) .

After a long while psu was connected, trigger was into r105 and speaker was on r296 .... r151 started burning.

I build everything in the procedure order, now I'm having issue just after the HCMA section, which is the last section i built.

Is there a link between the 4011 issue (r151 burning ) and my q28 burning up ?

thanks everybody !
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Re: Q28 burning & after a while R151 burns [SOLVED- PCB ERRO

Postby p4rancesc0 » Aug 2nd, '14, 16:43

Hello everybody,

after changing r151 and 4011 with and UB version nothing has changed for q28.
The build is unfinished and I'm not actually using the accent circuit. Really Hope that r151 issue will be solved with this.

In the mean while I experimented a lot with q28 & q29 and those 4 resistors around.

I managed not to burn q28 by using and old 1.5V battery for supplying the "+5V" accent to r103.
Damn it worked ! no burning transistors. But on the other instruments the voltage was too low (1.5V maybe :P).

At the end I found out that impedance from the TP on r103 (where I can attach my crocodile) and ground was 10k while on the other instruments was 32K (from accent input to ground).

Well, following the PCB layout if you attach a crocodile to r103 you bypass r0103 and you will put 5V directly to the base of Q28 making it burn.

My was 4TH batch, I can see differences in the shoot in building section and my PCB layout.

If you want to use r103 TP to supply 5V accent you have to invert the wire part and the resitor part when soldering r103.
I'm sure this is not clear, so I attach a couple of picture.

BEWARE !
from a circuit point of view everything was correct, the issue was only during testing.
The PCB is correct, only the R103 soldering tip (i.e advice) was inverted.

Can anyone confirm this ?


Anyway, now it's working :D :D :D :D :D :D :D :D
But the HandClap sounds like overdriven... this is bad :( :( :(

working-r013-TP_small.jpg
R103 inverted according to PCB layout, attaching 5V there is ok for Q28
working-r013-TP_small.jpg (57.38 KiB) Viewed 10677 times


NONWORKING-r103-TP_small.jpg
R103 soldered according to PCB layout, attaching 5V there is NOT ok for Q28 because will drop 5V directly to Q28 Base
NONWORKING-r103-TP_small.jpg (80.64 KiB) Viewed 10677 times
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Re: Q28 burning & after a while R151 burns [SOLVED- PCB ERRO

Postby ikke » Jan 11th, '15, 21:03

Can someone confirm this issue with the wrong orientation of R103?
:roll:

edit*
Nevermind, i found that this is the same fault with the silkscreenining on my PCB (v1.0).
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Re: Q28 burning & after a while R151 burns [SOLVED- PCB ERRO

Postby morecowbell » Jan 12th, '15, 23:21

Maybe I'm misunderstanding something here, but really the orientation of the resistor shouldn't matter, should it?

In the photos provided in this thread, you are testing the resistor at two different places depending on which orientation you use. You should be able to get the same results by testing the other side of the resistor, regardless of orientation.

Am I missing something here? If there is an issue with the boards, it would be great to know.

Thank yall.
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Re: Q28 burning & after a while R151 burns [SOLVED- PCB ERRO

Postby ikke » Jan 12th, '15, 23:52

If you follow the silkscreen, the outside of R103 will get exposed at the wrong side so you will bypass R103 (22k) and feed 5Volt directly
on Q28's base instead of being limited by that 22k resistor.
This will only happen when you test the instrument with an Arduino.
Otherwise you wouldn't notice the orientation is wrong.
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Re: Q28 burning & after a while R151 burns [SOLVED- PCB ERRO

Postby p4rancesc0 » Jan 13th, '15, 07:21

Great ikke, 100% correct
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Re: Q28 burning & after a while R151 burns [SOLVED- PCB ERRO

Postby qexuhiwu » Mar 20th, '20, 07:39

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