I prefer the diode since the volt drop is roughly constant (0.5-0.75V) whereas you might get 2 or whatever volts in a fault situation.
Are voltage measurements/results the same?
Are voltage measurements/results the same?
You should never power up a power amplifier being repaired unless you are very sure you found all the bad components. At a minimum current limit the power supplies.
A component tester, AKA Octopus or curve tracer in low voltage AC I/V mode should be used to screen for bad parts. Anything suspect should be removed and tested completely. Back in the day I only had a $10 Radio Shack VOM to check transistors and diodes for shorts. Today I use a Huntron Tracker to screen for obvious faults and then test anything suspect out of circuit with a curve tracer. You will not catch leakage or breakdown issues unless you test with a curve tracer. At a minimum, a component tester/Octopus is very cheap to make.
As far as buying replacement power devices, good luck. There are more counterfeit parts than real devices especially on eBay. Only buy from reputable vendors.
A component tester, AKA Octopus or curve tracer in low voltage AC I/V mode should be used to screen for bad parts. Anything suspect should be removed and tested completely. Back in the day I only had a $10 Radio Shack VOM to check transistors and diodes for shorts. Today I use a Huntron Tracker to screen for obvious faults and then test anything suspect out of circuit with a curve tracer. You will not catch leakage or breakdown issues unless you test with a curve tracer. At a minimum, a component tester/Octopus is very cheap to make.
As far as buying replacement power devices, good luck. There are more counterfeit parts than real devices especially on eBay. Only buy from reputable vendors.
I don't understand why if a replace original 2sa979 with 2 E com 2sa992 the voltage getting worse...... between -15 & -20v on E and B of output transistors.
All transitors are not fake, HFE 398 and 400....
Mystery.
But two 2sc1845 B com instead of 2sc2291 works fine and voltages correct.
Q3 and Q4
Q3
-46.1
-45.5
-45.5
-43.4
-45.7
Q4
-46.2
-45.6
-45.6
-43.4
-45.7
Now I put back the originals 2sa979 and 2sc2291 and voltage on E and B of output transistors is between +8v and +10v.
All transitors are not fake, HFE 398 and 400....
Mystery.
But two 2sc1845 B com instead of 2sc2291 works fine and voltages correct.
Q3 and Q4
Q3
-46.1
-45.5
-45.5
-43.4
-45.7
Q4
-46.2
-45.6
-45.6
-43.4
-45.7
Now I put back the originals 2sa979 and 2sc2291 and voltage on E and B of output transistors is between +8v and +10v.
Last edited:
I decided not to waste any more time with this amp. I ordered a class d amplifier and will put it in place of the original Help me please only how to connect the display. Without a power amplifier,blue display not work
A power amplifier like this has many feedback loops. Any bad or wrong component will disrupt the DC values throughout the circuit.
You will go down the rabbit hole once again if you try and substitute a Class D amp.
Trash the amp and buy something else. They are a dime a dozen on Facebook.....
You will go down the rabbit hole once again if you try and substitute a Class D amp.
Trash the amp and buy something else. They are a dime a dozen on Facebook.....
Ooooops....
''AB100 Class AB Power Amplifier'' by Mr. Nelson Pass.
https://www.diyaudio.com/community/threads/ab100-class-ab-power-amplifier.227503/
For example.
If I need to connect this Chinese Amplifier.
I have + and - 46v on PIONEER board.
And ground.....
how should i connect it?
Ground on - pin and +46v on+?
If I need to connect this Chinese Amplifier.
I have + and - 46v on PIONEER board.
And ground.....
how should i connect it?
Ground on - pin and +46v on+?
+1 for stopping and collecting your thoughts then formulate a systematic plan.
The SA-7800 is a decent vintage amp that deserves more "respect" than you are showing it.
Start by a clear statement of current situation, eg, output, drivers removed (replaced by?), powering up on DBT? DBT behaviour normal or remains bright, list of abnormal voltages and whatever else you think others might find helpful. Posts saying it doesn't work are not real helpful.
The SA-7800 is a decent vintage amp that deserves more "respect" than you are showing it.
Start by a clear statement of current situation, eg, output, drivers removed (replaced by?), powering up on DBT? DBT behaviour normal or remains bright, list of abnormal voltages and whatever else you think others might find helpful. Posts saying it doesn't work are not real helpful.
Yes,yes,yes it's working.
Its was microcrack on power amplifier PCB.
All voltages are ok.
Thanks for your help
Its was microcrack on power amplifier PCB.
All voltages are ok.
Thanks for your help
Seriously? Kuuuudos! And who exactly works - SA-7800 power amp or class ''D'' power amp? Good try....... Come on, just admit it😉. Don't mad, we will help you. You picked wrong time: The Holidays, low calorie cocktails, skinny cocktails, table water and other boozy drinks.......
. audiocircuit.dk/pioneer4/
Jan Dupont :
https://audiocircuit.dk/downloads/pioneer4/Pioneer-SA7800-int-asm.pdf
