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Old 28th April 2006, 09:44 PM   #21
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>what a headache

???
See, I fully disagree.
This is just part of the fun.
If it is not, then I don't understand anything of this passtime.

If you want to save your self this "headache", ....
buy an amp???

You say you matched the bc550 (useless I think) but did you just
take out one of the bc550 and checked it again?

I hate to say this, but I think you are going around this in a
wrong, and maybe a little sloppy, way. (no bad intentions)

In this light, rechecking all resistors with an ohm meter is probably
a good idea. But I wouldn't hold my breath.

I do not understand why you are saying " I am 100% sure that
....".
Being sure is good. Making sure, by rechecking, even if this means
taking one or all parts out of the PCB, is BETTER.

Realy no offence intended.
Talk to you tomorrow. And remember: Giving up is not an option!
:-)

Cheerup, please.
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Old 28th April 2006, 11:21 PM   #22
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Quote:
Originally posted by rtirion
Given +PWR = 26,5V and -PWR = -26,5V
Measurements ground referenced

>Gain mosfets Gate -25,7, Drain +20,8 Source -26,5
That's not good. Should be around:
Gate -21V, Drain 0V, Source -26V. In this case your source resistor
would be dropping |0,5V|.
Tells me that the differential pair is not conducting - no voltage across their load resistors (same as gate voltage in gain devices)
Quote:


>CSS mosfets +25,3 +25,3 +21,4
That's also not good. Should be around:
Gate +4,5V, Drain +26,5V (rail), Source +0,5V
This is a consequence of the gain devices not conducting - the CCS is trying to increase the voltage to get current to flow. That's why the 100R are hot.

Quote:

>irf 9610 (single) +16, +24,1 +24,1
Also not good. Should be around:
Gate +16V, Drain +4V, Source +20V
Way off, as you can see.
Again a consequence of the differential pair not conducting -

Quote:
>BC 550c transistors
>(Pair near 220uf electrolytic in schematic) E +21,2 B +21 C +25,1
No good. Should be around
E = 0V, B = 0,7V, C = 4,5V
There have been a lot of problems around these BC550C.
Given these measurements, this would be my prime suspect.
What brand did you use? Do you have the datasheet from the
manufacturer? Check the orientation again? Do not let the
markings on the PCB silkscreen, determine the correct position.
There are two types of bc550. Leads inline and Leads in triangle.
Pinning CBE for type one EBC type two. Which one do you have?
Fairchild, Zetex, Philips, Siemens? Allocate the proper sheet and
determine the correct lead out. Cross check with board pads.

Use a simple transistor meter to get an indication of gain
BC550C should have a hfe of 400 - 800. This way you know
which leg is C, B and E

The measurments on the diffpair are inconslusive.
two parts with exactly the same figures for G, D and S.
Not possible. Sources are connected, so they give same reading.
Drains should differ a little bit. Same goes for the gates.
Please repeat measurements around these.
The BC550C voltages seem OK to me based on the input differential not working. Notice that you have ~4V E-C, which is what it should be to get the CCS MOSFET to conduct. This CCS is upside down compared to the usual configuration - the current sense resistor is not attached to a rail, so you need to look at relative voltages inside it to determine if faulty.

Since both sides seem to be doing the same thing, it points to something they have in common.

My bet is on the input differential pair gone bad. Replace both of them and your amp should spring to life.
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Old 29th April 2006, 06:24 AM   #23
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good morning.

headache was from zens v4, i would like never to back to theese times.. there is lot of diferences between speakers and amps conctruction.. to but a new amp is not bad idea,just 5 aleph xa100 amps costs LITTLE too much for my wallet. and building myself I can put better details(manufacturers-can not.inspite how much engineers would like to put better parts , others do not let this. I have opened many xxxxeur and even few xxxxx amps, CDP and especialy speakers and find that)

I mached bc550c this way- tooked 200pieces, mached them to the same hfe, then mached again(because values difers), almos tall values differs , when I found 4bc550 c which measures constantly all the time I have a one pair. and then again .
I am sure 100% because I dissolder some of parts include bc550c to check, I do not want to desolder all parts but SOMWHERE i DID MISTAKE.and this was to all 10 boards.

now I am going to check it all again..
input diferential pair is pair 9610? when I measure i get very close values to all paired devices including 240 and 9610. maybe litle bit helped that I used 1% tolerance metal film resisitors and also mached them for pairs.




BobElis- how can irf9610 to break down? if this happens on one board I can understand,maybe accidently, but if on all that shuold be somewhere problems. but I will try replace 9610 with soem unmached .I will let you know results, thanks again..
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Old 29th April 2006, 07:36 AM   #24
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just checked 5 times bc550c pins, rchecked 5w resistors, eplaced irf9610 with new ones-all the same..
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Old 29th April 2006, 07:52 AM   #25
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Old 29th April 2006, 08:19 AM   #26
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Put all the boards away for a week, and spend some time off drinking beer, with your family or friends, or watching TV. Then, come back fresh, and with a clear mind, and the problem will probably be blindingly obvious.

BTW, I'm not joking, I'm being very serious...
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Old 29th April 2006, 08:26 AM   #27
Netlist is offline Netlist  Belgium
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And clean that bench first!

/Hugo
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Old 29th April 2006, 08:47 AM   #28
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would you recomend to alchoholic relax and take a good sleep, while botle of vodka is near?

I dont drink, dont wach TV, I can only go to sport, to run, but after 30km I think my mind will not be clearer,because I dont have clear minds regarding amplifiers, theese are brutual, and "mood depend on" mashines with no mercy to poor people

the only thing that goes to my mind is small resisitors. but what can be wrong with theese? and somehow I think(from expierence always fails transitors) that smth with tansistors.and the smaller transistor the evil minded it is.



seriuosly any inputs about whats is going on? can be irf9610 pins diferent from irfp240?
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Old 29th April 2006, 08:48 AM   #29
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Quote:
Originally posted by Netlist
And clean that bench first!

/Hugo

what bench?
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Old 29th April 2006, 08:59 AM   #30
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bc550 mounted like this?
top view.
Attached Images
File Type: jpg bc550-pc1.jpg (74.0 KB, 207 views)
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