| T.R | Title | User | Personal
Name | Date | Lines |
|---|
| 1767.1 | More info.... | SIOG::PKIRK | I wonder if I'm on the right planet......? | Mon Apr 09 1990 14:51 | 27 |
|
Hi Tom
Need more info....
e.g. what type of transistor? FET/MOSFET/BIPOLAR etc.
Are you sure its a transistor not an I.C. or a regulator.
Since you cant get power onto the amp. its not going to be very
easy to trouble shoot however you seem to have a short in there
somewhere. you will have to remove the transistor from the circuit
in order to test them using a meter accross the base and emitter
and across the base and collector ( collector is usually the case
ofthe device) keeping one lead on the base each time one side should
show very high resistance Mohms and the other low resistance. which
side depends on what type of transistor NPN/PNP. This all assumes
its a Bipolar type.
BUT.... if I read your note correctly you do have a good working
channel to use as a reference.......
How did you manage to blow the amp and why do you suspect the power
transistors anyway.....this will give some clues as to whats wrong....
Paul Kirk
CSE Dublin Ireland.
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| 1767.2 | My 2p worth. | CMBOOT::EVANS | if you don't C# you'll Bb | Mon Apr 09 1990 15:33 | 26 |
|
One trick is to put a meter on OHMS connect one lead to emitter &
the other to collector & touch the base, should make the meter deflect
to some degree depending in the type of transistor...trouble is this
must be done out of circuit & only really shows if it is totally shot,
ie if its just damaged & the gain is reduced there's no way of telling.
In circuit you could look for the 0.6 to 0.7 v between base &
emitter when the unit is powered on.
In some stereo units they use paired transistors in one package
(Darlington pairs) in which case both the above tests may give dubious
results.
The only real way to check a device out is to put it on a curve
tracer which will plot the characteristics under load & check it
against a manufacturers data sheet.
Peresonally I'd check out the price of the part & if it's not too
expensive try replacing it.
Sorry....not much help really but it may give you an idea.
Cheers
Pete.
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| 1767.3 | | IOENG::JWILLIAMS | Welcome to the Bush League | Mon Apr 09 1990 17:30 | 14 |
| A good way to trouble shoot a solid state amp is as follows:
Get a variac to power your amp through. Use an ampmeter to measure the
current going into the amp. Adjust the voltage on the variac so that
only a small amount of current goes through. Use a voltmeter and check
for shorts in the power supply. Check for correct bias on all the
bases, etc.
PS. Don't forget to figure out why your transistors blew.
John.
( Who's replaced blown Darlingtons after someone figured they would
plug in the external speaker jack before checking the wiring. )
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| 1767.4 | Thanks. | FSTVAX::GALLO | Bass: The Final Frontier | Mon Apr 09 1990 18:24 | 22 |
|
Re: How I blew it
I dunno, it just died. I wasn't doing anything special.
Re: Replace the parts
I would, except it has like 12 or so output transistors.
Re: Fixing the amp
Looks like it'll be more complicated that I thought. Since I have
one (400W) channel running ok, I'll wait until I can afford to
get it 'professionally' fixed. I might even sell it as it
is.
Thanks for the info,
-Tom
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| 1767.5 | what kinda amp!!?!?! | USRCV1::MCNALLT | MCNALLT | Mon Apr 16 1990 17:04 | 11 |
| What kind of amp is it???? I just finished fixing a Phase Linear 400 it
blew a couple of output transistors because the a 15volt zener died
causing the fist op-amp to go to the negative rail and since the amp is
direct coupled the output went to -65V.
I found that the transistors could be checked in circuit with an
ohmmeter. Put the meter in RX10 or RX1 neg probe the paralled
collectors and postitive probe on the emitters one at a time if you get
a reading less than about 800 ohms ( could be 2 ohms if something is
blown) look for the lowest reading (it'll be close) of the bunch and
remove it. If the original reading goes way up you found it!
|