Technics SE-A1000 troubleshooting, help please
Hi all,
So, short story;
I have a Technics SE-A1000 amplifier since 18 years or so. Bought it second hand in a really pristine state and have used it for a couple of years until it broke down on me. At that time I got myself another amp from my dad, so I putted the Technics aside in a storage box.
Now, 15 years later I really want to make it work again.
End of story.
Now the problem;
I opened up the unit and replaced the fuse with a F2.5A instead of T3.15A, just to be a little bit more protective the first time.
Like it was then, it is still doing the same thing.
When I put mains on the PSU, the standby led will light up. When I push the ON button, both VU meters go all the way.
The safety circuit is engaged immediately but kinda hard to tell since the fuse will blow right away (could be the charging of the caps etc). The capacitors are bleeding out, and both VU meters are gliding back to 0.
So it appears to me that there's a DC injection on both the outputs.
Now I have enough measuring equipment and schematics and a basic understanding of electronics, but to be honest... I really appreciate some help from some pro's or experienced people with troubleshooting Class A amplifiers. The circuitry is a bit more complex than I'm used to.
So far I have measured one and another. Started with measuring the voltages from the PSU and that appear all to be OK.
Next thing I checked the rectifiers D701 - D704. I had some notorious reading, but since there is a capacitor parallel on them, I took them out circuit en tested them all 4.
D704 failed on forward and backward. It is shorted.
Now I want to know why the D704 has failed on me. Is it because another component or just broke down and it will be an easy fix?
So, I will continue tomorrow with this journey since it is getting late. I would really appreciate some thoughts and suggestions.
cheers
Hi all,
So, short story;
I have a Technics SE-A1000 amplifier since 18 years or so. Bought it second hand in a really pristine state and have used it for a couple of years until it broke down on me. At that time I got myself another amp from my dad, so I putted the Technics aside in a storage box.
Now, 15 years later I really want to make it work again.
End of story.
Now the problem;
I opened up the unit and replaced the fuse with a F2.5A instead of T3.15A, just to be a little bit more protective the first time.
Like it was then, it is still doing the same thing.
When I put mains on the PSU, the standby led will light up. When I push the ON button, both VU meters go all the way.
The safety circuit is engaged immediately but kinda hard to tell since the fuse will blow right away (could be the charging of the caps etc). The capacitors are bleeding out, and both VU meters are gliding back to 0.
So it appears to me that there's a DC injection on both the outputs.
Now I have enough measuring equipment and schematics and a basic understanding of electronics, but to be honest... I really appreciate some help from some pro's or experienced people with troubleshooting Class A amplifiers. The circuitry is a bit more complex than I'm used to.
So far I have measured one and another. Started with measuring the voltages from the PSU and that appear all to be OK.
Next thing I checked the rectifiers D701 - D704. I had some notorious reading, but since there is a capacitor parallel on them, I took them out circuit en tested them all 4.
D704 failed on forward and backward. It is shorted.
Now I want to know why the D704 has failed on me. Is it because another component or just broke down and it will be an easy fix?
So, I will continue tomorrow with this journey since it is getting late. I would really appreciate some thoughts and suggestions.
cheers
Last edited:
Both sides?
Mmm check voltages to AN7062 to start
Check also these points.
Collectors on Q401, Q401 (2.4V)
Collectors Q451 Q452 (-2.4V)
Pin 6 and 13 On RSN6000 (0V)
SVI3205 Pins 15, 13 Inputs (0V), Outputs 3 and 6 (0V)
All voltage readings are between measured point and ground.
Mmm check voltages to AN7062 to start
Check also these points.
Collectors on Q401, Q401 (2.4V)
Collectors Q451 Q452 (-2.4V)
Pin 6 and 13 On RSN6000 (0V)
SVI3205 Pins 15, 13 Inputs (0V), Outputs 3 and 6 (0V)
All voltage readings are between measured point and ground.
As for rectifier diodes... I’ve seen them go short for no reason.... replace all 4 rectifier diodes
Solved
Luckily my order came in yesterday, 1N5402's
First I checked all the 10 diodes. There where some slight differences in the voltage drop. So I cherry picked 4 with a 'identical' value.
After soldering, cleaned the board with IPA and reconnected everything. Applied new thermal compound on the hybrid chips since I cleaned them for check. Replaced the fuse with the specified type and it went into operation mode after turning on.
I was amazed. 😀
Thank you all!
Luckily my order came in yesterday, 1N5402's
First I checked all the 10 diodes. There where some slight differences in the voltage drop. So I cherry picked 4 with a 'identical' value.
After soldering, cleaned the board with IPA and reconnected everything. Applied new thermal compound on the hybrid chips since I cleaned them for check. Replaced the fuse with the specified type and it went into operation mode after turning on.
I was amazed. 😀
Thank you all!