| cowanrg |
sigh. im always having problems it seems...
well, im testing my bosoz right now. its pretty much all built, just not in a case yet. however, everytime i test it, i blow a fuse.
i have done some troubleshooting and found that its not the preamp (when i remove it from the chain, and just have the power supply board and xformer, it still blows), and its possibly not the power supply board (the transformer alone blows fuses!).
so, i think after 8 fuses and a lot of head scratching, im using too small fuses? i am using 4A 125V fuses. however, as some of you know, im using a HUGE transformer for this little pre-amp. i have an 800VA transformer powering it. it seems that turning it on and off makes the fuse blow. but, when the pre-amp is on, the initial inrush current blows the fuse. im all out of fuses at this point. should i try it direct and see what happens? its only when i turn it on and off quickly that i get a blows fuse with just the transformer connected.
if i have the transformer and the power supply connected only, and have a meter on it, i get 80.5V (which is what its supposed to be), but the fuse blows JUST as it gets up to 80.5V.
what size fuse should i be using? i get a new digital camera (5.0 MP sony!), so i can take pics if needed. |
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| Cobra2 |
but wit that large trafo, you need SLOW fuses, and probably more than 6Amp.
Arne K |
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| Blues |
| check for shorts...check your semiconductors if they're mounted right (rectifiers and trans regulators). |
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| cowanrg |
yeah, im pretty sure they are. any huge risk of just NOT using a fuse right now to test? im all out of fuses, and certainly dont have any bigger than 4 amp.
the power supply runs for a second, the transformer runs 50% of the time, as long as it was already "charged" from the last turn on. (but if its cold, or was sitting overnight, it will blow a fuse...)
i just dont want to replace a circuit board. |
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| eLarson |
| Maybe a light bulb temporarily wired in series after the fuse as a make-shift inrush suppressor? |
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| cowanrg |
hum...
i guess i could try that. but if there's a problem will i be cleaning up glass? |
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| cowanrg |
| i think i failed to mention that after i get this working, i will finish my aleph2's! so, if anyone wants to see them done, you can help me out a bit :cool: |
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| cowanrg |
so i think it was just the fuse size... i tried it without a fuse, and it seems to work just fine.
however, im getting another issue...
my voltages are pretty far off on my power supply...
i read the manual on passdiy and am following the directions pretty closely. i did what nelson says to test it loaded (put a 15kohm resistor across the positive and ground and negative and ground) and measure the rails and the regulated rails.
i am supposed to get +-80v unregulated and +-60v regulated. this is a dual mono, so on PSU1 i am getting 84.8V rails (within reason), but +40.23 and -40.00 on regulated rails. (i should be getting +-60v). on PSU2 i am getting 85.3V rails (close enough i guess), but -55.3v and +47.7 on the regulated rails. these arent very close, nor do they make a whole lot of sense.
i spot-checked a few of the zeners and they all seemed to be getting about a 6.2V drop across them. the only thing that i can think of would be a bad transistor or a bad zener, only because thats what has happened to me before :) help would be greatly appreciated. |
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| BobEllis |
The zeners should be 9.1 volt types. looks like you got some wrong parts in there.
Your rail voltages make sense when you consider a 5% tolerance with a couple of 9.1 volt types sprinkled throughout. Output voltage will be the total of the zener string minus the gate-source voltage of the pass transistor.
your unregulated voltages are high because you aren't loading that monster transformer down much. watch the heat sinking on Q101 and Q102.
As for your fuse issue, a CL-30 in series with the primary and 6 amp slow blow fuse ought to do the trick. |
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| cowanrg |
ok, that makes more sense now...
in the papers for the preamp (which i am re-reading and trying to understand), it states that there is a 3.7v drop across the gate to source, and there are 7 9.1V zeners (63.7v), so it should give 60v. hum. im going to measure my drop from gate to source, and see if its 3.7. and ill take out some of the zeners and measure them again.
im pretty sure they are 9.1, thats all i have in my shop. i thought i had the wrong value before, so i bought some more and tested them to make sure. i have like 50 of the things in the shop, and they are all tested at 9.1v (or they were). |
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| BobEllis |
| quote: | Originally posted by cowanrg
i spot-checked a few of the zeners and they all seemed to be getting about a 6.2V drop across them. |
| quote: | | im pretty sure they are 9.1, thats all i have in my shop. |
those two lines don't compute ;)
Wouldn't be the first time the wrong parts were put in the bag at (insert favorite supplier name here), though. I once got a bag of mostly pnp darlingtons when I'd ordered (and the bag was labeled as) NPN small signal types for my Leach inputs. there were a few of the proper part in the bag, too. |
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| cowanrg |
hum, ok.
im still new to all this testing stuff... im just ignorant to it, and im not sure if IN the circuit they measure differently... but i guess once i think about it, a 9.1v zener should always have a 9.1v drop across it no matter what circuit its in.
SO, i tested things again. i measured the drop across gate to source, getting anywhere from 3.6 - 3.8 loaded, which is right in line.
i retested the zeners, and sure enough, some test at around 8.8v drop, where others are 6.2v drop... so, i guess i have some bad/wrong value ones. i will just reorder all new ones.
i hope that works!
ive had SO many problems with zeners! |
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| BobEllis |
sounds like you're on the right track.
Yes, you should get the same voltage however you measure a zener, as long as you've got a minimal current through it.
So I expect to see those aleph 2s next week.:) |
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| cowanrg |
haha, me too!
i think i might do 4 of them for myself, and sell the 5th chassis. who knows though...
i think i will have the same guy who did the faceplate do the rest of the chassis too... that will take a LOT less time, and it will be cheap too. we will just have to see...
gotta finish this darn pre-amp first! |
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| Blues |
| quote: | Originally posted by cowanrg
ok, that makes more sense now...
in the papers for the preamp (which i am re-reading and trying to understand), it states that there is a 3.7v drop across the gate to source, and there are 7 9.1V zeners (63.7v), so it should give 60v. hum. im going to measure my drop from gate to source, and see if its 3.7. and ill take out some of the zeners and measure them again.
im pretty sure they are 9.1, thats all i have in my shop. i thought i had the wrong value before, so i bought some more and tested them to make sure. i have like 50 of the things in the shop, and they are all tested at 9.1v (or they were). |
You most likely installed 6.2V zeners on the regulated rails with 40V or so. On the one with 50V one 9.1V zener must be in the mix with 6 other 6.2V zeners. |
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| cowanrg |
yeah, after reading a bit more, thats all i can think of.
i do have a diode tester on my meter, but im not sure how to interpret the results. when i test the diode with the diode tester, i get about 0.721. im not sure how to read this. is there a way to tell if that's a 9.1v zener or whatever? or is that information just not useful at all? |
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| BobEllis |
nope, the diode tester is worthless for checking your zeners. Just measure the voltage across them while in the circuit. rail votage or zero indicates a bad zener, anything else is its zener voltage.
A trip to radio shack or equal is in order to get a string of 9.1 volt zeners. (assuming you don't want to wait for shipping) |
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| cowanrg |
| yeah, i have a few local electronics shops nearby, or radioshack. the surplus shops should be cheaper though, maybe only $0.05 each zener. but then again, that's where i might have gotten the wrong value ones... |
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| Kermit |
| If you want to test the zener diodes before soldering them in, connect a resistor (2k - 3k or so) in series with the diode and connect to +12v. Then measure the voltage across the diode. |
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| cowanrg |
| i think im gonna get a small breadboard, so i can have a small curcuit to test transistors and diodes out of a circuit... |
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| Blues |
| 0.5v to 0.7v across zeners with a diode tester means they're good. zeners if you look closely are printed with their part number...you might need a magnifying glass. |
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