BACK TO STEREO

Lunch break was spent assembling one tonearm from three – one was with broken off counterweight, another with damaged microlift… finally, the tonearm assembled , in place, secured, turntable assembled. All we need is to attach the pickup, make tonearm adjustments, and – that’s it!

Uh, doh, forgot – the dust cover! But that is the last item.
More pics.
Regarding the second Technics – I decided to repaint the body of the turntable as the 34 years of age were clearly visible. All the lettering was scanned in high res, appropriate fonts were matched. Decent silk screen services in Riga, anybody?

The pics are @picasa, as always.
The practically identical SL-1500/1510 both suffered from the Parkinson of drive speed stabilizer circuit. It couldn’t remember the correct speed. So, a number of replaced caps later…

There is another PCB with original caps still onboard. Only one replaced by new Long Life RIFA is the ripple filter 470uF cap.

When you come across a particular device where all the transistors in one channel are blown, you may to start wonder – why?
A little later — when you have replaced them all with new ones, you discover – the problem is high frequency oscillation. Amp effectively becomes the VHF generator – for a short time.
I see the problem being the two stages of amplifier built on two separate PCB, connected with a kind of PCB bridge. 2 x 16 contact pins – all of them losing contact due oxidation sooner or later. See the attached pics and schematics. High-voltage circuit, ground and feedback loop – all are connected via the same PCB bridge. No wonder the result is fatal if something goes wrong or contact is lost due oxidation.

This was supposed to be a 0.01uF capacitor. Is it?

As always, more high res pics available at Picasa

Tonight I started the assembling of cleaned and repaired receiver. Both power amp section and tuner section works well. It delivers 15V RMS on 6.8Ohm dummy load without any clipping. U**2/R produces 33W of pure RMS power, not “DIN” or “musical” or other mystical PMPO kilo-Watts…. It is pretty decent for such a small piece of equipment. So, dials, LEDs, bulbs, new caps for ripple filter and in power stage audio circuit are in place, final tweaks tomorrow. Gosh, I forgot to check phono preamp section. Well, tomorrow, as well.

Temporary set for hobby room.

So, for those interested – the inside of SANYO STK-463. Unfortunately, not short-circuit proof, but overall a neat little 2 x 30W amplifier module. You can see the four power stage transistors and a lot of SMD resistors and transistors.

Iegādāju eBajā pa 1 EUR iecienīto tuneri. Izskats smuks, iekšā nekā tāda īpaša. Nu neiet, kā raksta vācietis. Iedomājos šā skrobi, kad bija uz pastu ar šo jāstiepjas, par to 1 EUR, bet dīls ir dīls.
Atnāk ar LBSS. Atrauju vaļā (vispirms) un slēdzu iekšā (tikai tad). Toč neiet. Deg gan viena lampiņa. Bet tas arī viss. Nu ko, zelta kokles, tfu, testeris rociņā un sākam mērīt. Atraujam desktopā vaļā servismanuāli. O! Ir, trafs, taisngriezis, stabilizators. Mēram, IrOkejs, maiņstrāva ir, līdzstrāva ir, stabilizējums ir. Paskrollējam shēmu – māāāt! Tas viss (tilts, kondensators, 3A tranis Darlingtonā, stabilitrons, rezistoru sauja) – lai nobarotu ar stabilu stabilizētu līdzstrāvu 3 gabalas 12v 125mA pilotlampas.

Tā, kur tad mums te barojas pats uztvērējs? Aha, reku aiziet uz lielo plati viens vadelis. Un tur – khe, vienpusperioda viendiodes taisngriezis, C, 2 pretestības un 1 zēners, kā arī viens tranzistorelis. Uz C spriegums ir, uz B un E – nulle.

Mans līksmo, tipa, tuneris jau salabots. Izvelkam stabilitronu a.k.a. zēnerdiodi, oriģinālu nomēram – īsais. Laukā, jaunu iekšā, O! ir barošana. Viss kā vajag, 17 V iekšā, 11.8 laukā.

Bet nu izejā joprojām ne mārrutka. Tuneris kā beigts. Tik lampas smuki spīd, sabarotas ar stabilizētu līdzspriegumu.
OK, skrollējam shēmu tālāk. Pamērīsim ka spriegumu uz FM demodulatora mikrenes un uz tranzistora, kas iededzina lampočku STEREO. Nulle. Kā – nulle?
Faak, es tak nupat kā salaboju barošanas stabilizatoru. Ā, te tak shēmā uzzīmēts – gribi FM, ieslēdz slēdzīti. Tad caur to strāviņa smuki iebaro FM daļu. Gribi AM – slēdzītim otra pozīcija, tad elektrība aiziet uz AM mikreni. Taupīgi, odnako, elektrība tak dārga. Mudrennije japonskije inžeņēri. :-)
Labi, uz slēdzīti ļepezdrība pienāk, bet no slēdzīša neaiziet. Pareizāk sakot, tur divi slēdzīši, otram virknē elektrība no pirmā padodas, tas nodrošina FM AIZVER MUTE!
Izsildam ar lodāmuriņu slēdzītim kājiņas, un tavu prieku – FM parādās, bet… tikai mono versijā, tikko kā otro slēdzīti ieslēdzam STEREO – Auto MUTE, tā tuneris DEAD. Pie tam barošana nokrīt uz ~ 1,5V. Neko sev slēdzītis, riktīgs MAGIC/MORE MAGIC.
Pamēru – toč, īsais uz zemi. Izjaucu – un tur starp korpusu un (slēdzītis tipa P2K) to plastmasas štoku dzelzs skaida. Kā slēdzīti nospiež, tā jamā – čiks un samet barošanu uz zemi ! 8-/
Īsumā – mēri ko gribi, bet labojot hlamus, fīlings vajadzīgs. Un to dod tikai ilggadēja pieredze.

Smukās bildes kā allaž te.

Take a look at the pictures below and leave comment, why I bought another STK chip today, to replace the one I used as a replacement yesterday… if you dare!