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Purchasing Sony ST-A6B - please help

EDITED POST:
Hi to all again,
I have STEREO :))) . Thank you all.
I twisted the 301 variable resistor until i heard in the headphones STEREO. Very close twist: about 2 mm from the last position.I gave it also an gentle clean.Another sound.

problems remaining
1) not working 5 bulbs and
2) the recap i plan to do. (very busy in my usual life .. 4 children and 2 business to drive.)


I do not managed to change the bulbs
In this thread https://audiokarma.org/forums/index.php?threads/st-a6b-sony-tuner-recap-list.684968/ i found 5V for the stereo bulb.
But when i measured with my multimetre/DMM between bulb wires i found 15.8 V. I do not understand why.
I'd try some new bulbs but i don not have/ found locally such value 5v or 15.8 V
I have only small and classical diode LEDS with 1.6 V and i will try to calculate an resistor to put in series with the LED.


Also VISUALLY , all the filaments from the bulbs ( stereo normal narrow bulbs) are ..intact, not broken. And i have 15.8 V on wires which feed each. No visually damage on the PCB, no burned resistor, no bad caps.
Strange that ALL upper bulbs are not working ( except the dial tune bulbs)


PS. i have in near future plan to buy an portable osciloscope with signal generator. ( not very expensive and i will use for other repairing projects) i found reasonably priced Owon HDS242S ( 2 channel 40M and function generator)


Thank you
 
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Glad to hear stereo is working. In many cases, especially stereo, there is a + voltage on one lead of the bulb, and the "switch" to turn it on competes the path to ground. In most cases, that switch is really a transistor. Use your multimeter to test resistance across the bulbs, it should be low, not open. But disconnect one bulb lead first.
The voltage and current of the bulb rating is important. Usually you can use higher voltage ratings, they will be less dim. This is trial and error if no one worked it out before for LEDs
 
Hi, ( short on time as usual)
I bought some new and small bulbs who tolerate 2V-12V
I connected one to the wires of stereo bulb...but the new bulb is lighting all the time no matter it is stereo or mono.
Any thoughts?
 
Hi to all, i am back here
i just ordered last night an quite large order from Mouser Europe for a big list of capacitors to recap 3 tunner:
Sony ST A6B
Mitsubish DA-F
and
Sansui TU x-701
I payed in the night with my wife card :) and in the morning she asked me: what is ..a mouser :D? with a value of 120 USD ? No, is not a "fuuurr" even is close to "MOUSEeeerrr"

Any thought about my last comment? Why when i connect an new bulb ( it support 2v-12 v) it is lightning continuously? Even if is no stereo signal , or no good signal at all?

Thank you
 
Hi Bob@FM :)
Yes i have stereo now. I have about 6 pdfs with skematics but i do not found the information about voltage you gave me. On the hifiengine are not allowed anymore registrations.
So i f i understand correctly : on the same wires , when my tuner is tunned to a stereo signal the voltage on the bulb wire will be 1.4v? and if the reception is not in stereo , the voltage will be on normal voltage on the same wire? I thought the concepts is open /close circuit but it seems that it is wrong( what voltage means normal here ?)
Maybe this is the explanation that i have always the LED open , because it have an large field of voltages. The led is working something between 1.5v and 12 v so even i have mono, even stereo, the voltage value will open the led.
Is this right?
If so i canot find a more restrictive led..I will search.
Thank you for the tip
 
The attached picture may help explain better. The values in red at the pins show typical voltages for the Sony ST-A6B MPX chip section.

Mono values or ones that do not change are shown normal. Voltages that change for stereo mode are in brackets like this <1.4v>

ST_A6B.jpg
 
Woow Bob, Thank you
I did not saw the schematics and red and the red notation's even I have that pdf..
I will study it.
 
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