Technics SE-A1000 MK2

Eastham

More Class-A than ever!
My friend is dropping his SE A1000 off with me tomorrow to take a look at because "The lamps don't work anymore" he also told me that he paid someone to do an LED conversion and they worked for a short while and then just went out.

Now I'm guessing the person he paid to do this was an idiot and messed up somehow, looking at the schematic I've noticed the lamp circuit has no protection at all for the transformer, this has me really worried, does anyone know if their is any kind of fuse that the SM is failing to mention? If not I'm hoping that since these lamps are in series that the first LED's in the string for each side have burned out. I'm also worried that the winding in the transformer for the lamp circuit has blown.
 
The transformer windings should be very easy to measure.
Other than that it is always a good idea to put a small rectifier bridge with a voltage regulator in series with the LEDs: they won't flicker anymore like that and the regulator also acts as a nice overvoltage protector.
 
The transformer windings should be very easy to measure.
Other than that it is always a good idea to put a small rectifier bridge with a voltage regulator in series with the LEDs: they won't flicker anymore like that and the regulator also acts as a nice overvoltage protector.

That's pretty much what I was thinking, a 3 amp rectifier, a 12 voltage regulator and a cap for smoothing, I like to use 100µF and some Fuse style 12v car LED's. I must admit I was a bit shocked that the lamp circuit runs at 33v.
 
Orright it's a series/parallel - L + R ch lamp pcbs are in parallel.... each pcb has FIVE 8V axial bulbs in series.
 
Interesting that they're 8v bulbs perhaps the lamp circuit isn't 33v like the service manual says an error maybe?
 
My SM lists 38.2V from T1 RTP1P5B005-W (for USA 001-W) CN754 & CN755

Oh is it 38? I couldn't read my SM, it was a bit blurry and broken up,looked like 33v. Thanks. Just waiting for said friend to drop it off.
 
Chances are your house maybe under voltage during your testing..... it has happened to me.... benching a commercial power amp nothing made sense... on AC in there was 90V AC instead of the nominal 240V.... turned out ther was a power pole down the road w/ a bad connection
 
All is good then... I'd replace ALL bulbs.... then all will light EVENLY.... let alone old bulb filaments get very brittle, and in series will blackout one side
 
That's the problem, friend said he sent it to someone to convert it to LED's and it failed shortly after he started using it, I'm kinda worried that this "Tech" wired it up wrong and caused the transformer winding to roast itself. Time will tell, he should be here with it soon. I'm, hopeful the tech used a resistor to drop the voltage and it's roasted instead of the trafo coil, or the first set of leds for each VU meter have burned out.
 
This is why I never convert to LED.

Power it on and check for AC voltage on CN754/755.

The massive flaws in this forum are re cap addicts, led converters, and the anti power ic masses....

If making ANY modification, ABSOLUTE CERTAINTY is completely NECESSARY. Fail this for further issue(s)
 
This is why I never convert to LED.

Power it on and check for AC voltage on CN754/755.

The massive flaws in this forum are re cap addicts, led converters, and the anti power ic masses....

If making ANY modification, ABSOLUTE CERTAINTY is completely NECESSARY. Fail this for further issue(s)

I must admit I'm guilty of being a serial re-capper... But I can agree with you on the rest, I only convert to LED if it's cheaper or I can't find original bulbs and as for the IC's I love my little SA-400 with it's pair of Darlington STK 0040's crackin' little unit.
 
Darlington power ICs are the best... my fave amp the SU-V4X is on a 2ch Darlington power IC - complimentary symmetry with synchro bias & overload detection.

This set uses 2x 12V axial bulbs behind the "new class A" logo..... if they both fail, it will be dark. Where as your amp, one fail will leave one whole side dark..... be happy you don't have a SU-V909... failure of the axial bulbs behind the "new class A" logo will stop the amp making sound (no relay controller)
 
Ha ha, wow. Technics had some crazy designs. I used to have a SU-V3, I remember that was a New class A, sounded really good. All Technics amps sound good to be honest, I don't think they get the credit they really deserve.
 
The V909 is the only model I've seen stop due to frikkin light bulbs....

1978-1985/6 were the best. New class A definitely had a sonic edge over the latter class AA, which I have a number of ppl asking of repair questions.... class AA was a whole different topology, much more complicated, I still do not understand why they switched to it... any class AA model released, there was a better new class A (earlier) variant in its range
 
I guess Technics thought two A's was better than a New A... Or maybe Class AA was just more Class A then New class A. :rolleyes:
 
Nah... class AA was a current correction amp, the short story is it's much more complex

A 15 watt or so Voltage amp (some cases MOSFET) drives a speaker via a Wheatstone Bridge, volt drop over the bridge is cancelled/"corrected" by a BiPolar output stage "Current Drive". Complex circuitry in relation to the new class A series, which often had the edge in sound
 
Well explained, that's exactly what Class AA does: a class B stage provides the current, and a small class A stage fills in the low volume parts where the B stage would start to produce crossover distortions.
New Class A instead was a conventional output stage, but with added synchro-bias circuit and variable idling current.
Then there was Class A+ (SE-A1 only), which was a class A output stage with its supply rails fed by a class B stage, which in turn was controlled by the audio input. Basically, the B stage acted as a power supply that would provide current only during loud passages.

I would say that out of the three New Class A is the simplest in terms of parts required, as it only needs one output stage. I almost adore the other two topologies; Matsushita engineers were true geniuses! My main amp still is a New Class A device. I never ever heard any sound differences anyway—even compared to conventional class AB. I believe that one's able to create "good sounding" amps (that is, good measuring), no matter what (audio-usable) topology one's following.

Most likely Matsushita switched to Class AA for marketing reasons: at some point the SE-A3MK2 was in need for a replacement (marketing-wise, that is), so goodbye New Class A, hello Class AA (with the SE-A100). They even built this into their tape and CD players, preamps and tuners, believe it or not! Why they just didn't use a conventional class A stage in there is beyond my understanding. Funny thing is that they continued using New Class A stages into the mid 90s, albeit only built into the lower end units (higher-ended ones had indeed Class AA stages).
 
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