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Pioneer SX 780 issues...lights up no sound !!!

R

ryanframe

Member
Pioneer SX 780 issues...lights up no sound !!!

I know this has probably been gone over before but is there a very economical fix to this how much and what does it take?

2 problems: no sound from headphones or speakers and the far left light is burnt out....the fuses dont look burnt(if they are suppose to look like a burnt light bulb)

I cleaned thoroughly last night hoping that would do the trick :(

Please help with common issues and diagnosis if available.:scratch2:
 
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first start by pulling fuses one at a time and test with a test meter . do this with amp unplugged .
fuses might look good to the eye but can be bad .
do you hear the relay click after power on ?
 
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Well....I dont have a voltage meter (yet) so my expertise hasnt gone past a lil deoxit....should I just buy some fuses? What kind do I get?...Thanks for your reply
 
do you hear the relay click shortly after power on ?
if you were to get a cheap basic dmm it would be a good start ..
 
If the panel lights function correctly that proves two fuses are good (2 & 4). If the tuning meter moves that MAY prove the other two fuses are good since there is some voltage at the tuner section. If the mode indicator lamps also operate that would be further evidence that the fuses are good.

It would still be best to verify the integrity of the fuses. The best way would be with an ohmmeter, and acquiring a low priced multimeter might not cost much more than set of potentially unnecessary replacement fuses. If you are thinking of replacing the fuses, you already have a Phillips screwdriver.

Your multimeter would be used to test AC and DC voltages at various point in the circuits. While you are out shopping for your meter (or borrowing one) you can start the download of the service manual from Here and get a copy of This Schematic.
 
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common

Use the google search here on AK for SX-780.
There are dozons of threads about them.

One common problem is the voltage regulator solder joints go bad.
I've "fixed" them by fixing that problem.
I've seen bad caps on the relay.

There is probably a thread on how to check the voltages on the power modules. (BE SURE to do that carefully! IF you short the pins, you can blow the module. Cover the probe with het shrink or tape all the way except the very tip!).

MTF must have walked scores of folks through repairs on those.
 
the aforementioned voltage regulator solder joints are on the underside of the circuit board where the three 1/2 inch square power transistors mounted on shiny U shaped pieces of aluminum all in a row are mounted. They crack and open up.

PULL POWER PLUG OUT OF WALL before soldering them!
 
...IF I find that the Darlington's are bad...can you tell me where to get the best replacement parts for this.....please PM me if you cant state in thread.
 
Ive read where some people say the $7 replacements are no good, does anyone have any experience from these...I saw a site that is a vintage stereo site with a tree as the name hint hint not Palm Tree Vintage but another tree, that has them for around $30 I think they might be from original receivers but am not sure....:scratch2:
 
yup, and be VERY careful when probing around them to read voltages - one slipp with a short = zappppp.... INSULATE all but the tiniest part of the tip of the probe. we ALL slip when we READ the meter....
 
Thanks for the confirmation guys that helps out alot....I am still waiting to get a voltage meter to test first before I take the plunge :)...........Love your site Larry its very impressive !!!
 
Ok Im getting a lil confused (over analyzing) ...How do I insulate the tip and what part do I test on the Darlington pack...still havent checked the fusesyet(2 of the light bulbs inside lightup when on the far left does not, there is no click either)....So I am at 2 ponts here; Test the fuses and test the voltage on the Darlington Packs....can you simplify this process for me its just not sinking in lol.... Thanks guys:thmbsp:
 
you can insulate the probe with electrical tape or wire shrink wrap ..all but the very tip so to minimise any shorting risk .
first test fuses ..if good proceed with the below ..if bad report back first with fuse number/s ..

meter set on 200v dc ..
power on the amp
black lead on metal chassis ."that is ground" red lead on pin 2 .expected -34v to -40v
black lead on metal chassis red lead on pin 9 expected +34 to +40v .
repeat for other power pack
report back with your readings .
 
ryanframe said:
Thanks for the confirmation guys that helps out alot....I am still waiting to get a voltage meter to test first before I take the plunge :)...........Love your site Larry its very impressive !!!
Click to expand...

Site?!:confused:?!?!:worried:??????? What Site??!?:dunno:!??????
 
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