sony ESamp cracles & sparks at RIGHT speaker terminals

[pickup]

hi guys, i have a sony ES stereo ampliier model TA F 555 ES, i made in japan, i imagine its about 15 odd years old.
after laying not used for about a year, it was making a crackle when i turned up the volume. a guy was thinking of buying it off me [he was just a sales assistant at a retravision shop].
he took some covers off an sprayed the volume contol and the crackle stopped. then he said the amp turned the music off after running for a few minutes.
then he said he took the cover off again,and seen two switches near the volume control and for some reason he moved one switch to 'up".
i got it back and have had the top cover only, off but cannot see the switches.
When i connect speaker wires to either of the RIGHT terminals -A or B, the speaker makes a loud crackle noise and there is a spark at the wire.
i have connected the speakers to the top and bottom LEFT speakers terminals and the amp and speakers go continuosly..
is anyone familiar with the amp, could him moving a switch up cause the crackle, and would anyone know where the switches are? i have only had the top cover off. many thanks in advance. ron

[Frank Berry]

This is merely a wild guess.
The switches may be for voltage selection.
Placed in the wrong position they could spell death to the amplifier.

[pickup]

thanks frank. on further discussion with the guy who looked at the amp. he thought the switches were some sought of protective device and one had popped up, and he depressed the button to match the other switch/device.
so probably not much to do with the fault i have of sparks at RIGHT speaker terminals ,together with loud crackle noise.

[Nico Ras]

Originally posted by Frank Berry
This is merely a wild guess.
The switches may be for voltage selection.
Placed in the wrong position they could spell death to the amplifier.

AS FAR AS I CAN RECALL THERE ARE NO SWITCHES INSIDE THE AMP. IF HE SAYS HE MOVED THEM LET HIM TELL YOU WERE THEY ARE. IF THE AMP WAS MADE FOR INTERNATIONAL SALES THE VOLTAGE SELECTOR IS A ROUND CIRCULAR SWITCH AT THE BACK ABOVE THE POWER LINE GOING IN.

CHECK THE VOLTAGE ON THE OUTPUT TERMINALS ON THE RIGHT HAND SPEAKER (ONE NOT WORKING) YOU SHOULD GET ONLY A FEW MILLI VOLT.

ON THE MAIN POWER AMPLIFIER BOARD THERE ARE TWO TRIM POTS, MAYBE HE REFERRED TO THOSE. IF HE ADJUSTED THEM THE BIAS COULD BE WAY OUT. THERE ARE TWO MEASUREMENT POINTS PRINTED 5mV. YOU CAN CONNECT YOU VOLTMETER THERE AND MEASURE IT AND ADJUST THE POTS TO PROVIDE THE 5 MILLI VOLT.

A 15 YEAR OLD AMPLIFIER COULD HAVE PICKED UP A LOST OF DUST AND MUCK, THIS COULD BE RESPONSIBLE FOR CAUSING CONDUCTING DIRT TRACKS ON THE PCB AND COULD AFFECT THE OFF-SET. TRY BLOWING THE BOARDS CLEAR WITH COMPRESSED AIR, YOU CAN GET IT IN AEROSOL FORM.

FINALLY THE AMP USES A VERY ELABORATE SPEAKER PROTECTION AND EVEN A SMALL DC OFFSET WOULD TRIGGER IT.

[pickup]

NICO, your correct, there are no switches inside. there are a couple of rectangular grey objects with a coloured button in the centre which he said popped up . you remember this amp pretty well.
they are probably some sort of protective device, and he reset one of them.
and there is no voltage selector.
i am not too good with voltmeters, and ohmeters.
at the right speaker terminals [ the ones not working] i am getting a reading of 60 volts DC. ???? this sounds far too high from what you mentioned.

On the main circuit board i can see two rotatable white plastic screw heads with a cross in them for a phillips head screwdriver.
i imaginr they are the trim pots you mention.
unfortunately, i am not familiar with audio equipment.
i will blow- clear the circuit board with a small compressed air gun as you recommend.
you also mentioned an elaborate speaker protection and a DC offset, can you expand on that and the voltage of 60volts DC i am reading at the right speaker terminals. please stay in touch you have been very helpfull. best regards ron australia
email : rcur3463@bigpond.net.au

[jaycee]

If you are reading 60V DC at one of the speaker terminals then unfortunately that means that the channel is damaged, and the amp requires proper repair. This is why the protection device will have tripped.

[Corvus corax]

Toast. Likely output device failure. The protection device either limited current to the loudspeaker or the output stage itself. DC, especially at full rail voltage- present at the output terminals usually points to bad output and/ or driver transistors. Easily repaired by a competent (component level) service technician.