Technics SU-V1X – No Power

A nice 40W monster from the 80s! Was working – stored for years, now not turning on after the last owner tried to recently…allegedly…

Poor old bugger! Look at the dust in this thing – no wonder it won’t turn on!

First thing – get the hoover out…!

That did not work at all – it’s that sticky, greasy shit – so acetone, contact cleaner and a brush required…and a wide open window!

Year: 1985

I’ll check the big 6600uF, 56Vcaps first as there’s an easy underside panel removal for that – these are in good shape – 0.003 and 0.004 ohm ESR and the dual PSU DC will help reform them – they should be changed as they’re 35 years old if original:

Now clean enough to work on (fuse is OK too), it can be powered to 30V DC gently by dual rail PSU across the rectifier diodes.

This is one of those 4 legged beasts like in the SA-5L that is difficult to get croc/scope leads on the legs – had to use pliers then make really sure the insulation was over the crocs to not touch the AC in legs.

It powers to 30V with no drama, but no mains bulb.

This is a 12.6Vpp AC from the PT so should be replaceable by an LED:

Note the 145C thermal cut outs, the thermistors on the small board test unblown at 39K each:

12Vpp / root2 RMS  = 9V RMS. V=IR 9V/0.02A (max LED current) =

450 ohm limiting resistor. Went with a 410 ohm.

Unfortunately, the LED didn’t sit centrally when clipped back in so not all lettering is lit well, but better than nothing…

Running off the mains shows all PT pins have the correct voltages referenced to ground (black).

 

 

The diodes are:

D505-8 all check out rectifying from 0V-(-/+7.5V)(+/-15V). The caps nearby also have expected values..

Assumptions again! There are NO LEDs on the front (my eyesight is getting BAD!) to imply channel logic switching (as on the last amp I was looking at – talk about going senile..) so there actually is NO problem with this amp at all now it seems!! That’s also letting the seller’s opinions affect your perception – he just turned it on, saw no light and assumed dead I guess? All that was required was to switch the speakers on at the front, probably!

Read the bloody schematic Steve!! The schematic shows the Voltage amp AN7062 pinouts (all correct within tenths V) AND the 16 pins for the SVI2003 itself (all correct).

So, now I have headphone and speaker outs, with an output of 45Vpp I can attach the 8 Ohm loads:

Power Out:

44Vpp = 22Vp = 15.556V RMS

P=VV/R = (15.556)^2/8 = 242/8 = 30.25 Watts per channel full volume.

Hmm..that’s MUCH lower than the 45W specs and with a 500mV input…??

Lesson Learned

I didn’t know the RIAA filter was in the feedback circuit of the phono op amp.

Usual idiocy by me making assumptions so fault finding when I didn’t need to, but good experience for logical voltage checking, non slipping probe practice and familiarity with the different pin voltages of the different SVI models and diodes – and new components – the Voltage Amp AN7062N and the 145C thermistors measuring 39k Ohms at room temp.

A good amp for a beginner to fault find as all components are accessible by a sharp probe and the schematic is detailed with all voltages at all point for this:

hfe_technics_su-v1x_service_en.pdf

The LED light now adds a custom aspect to the front. Blue always looks good! Would have been nice to have channel select LEDs on this model. The -20dB cut switch with Loudness on is really effective in reducing noise from a badly tuned S-5L!

The rectifier ripple is 130mVpp on the +/- 35V DC rails:

This will need filter caps replaced I think, despite good readings if they’re original at 35 years old as there is a nasty mains hum sometimes at power up that can shut the amp down. I’ll order them now. This may be a cap temporarily leaking noise onto the rails if it’s breaking down at powerup?

Don’t think it’s a diode breaking down else I think that would likely be a permanent fail?