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Transformer buzz when I conect speaker and I have to turn amp on first or speaker protection kicks in.
It must be something I have got wrong but all components are as printed on pcbs and both pcbs do exact same fault.
I get 0.8v dc with speaker conected and 1.5v dc with no speakers conected.
Things I have tried is removing soft start ,speaker protection and fan pcb all at same time so it was just running on power supply.
Still exactly same dc at speaker readings.
I can get dc to go up by adjusting pot to 2.8v but it wont any lower than 0.8v.
Speakers are 4 ohm wired in series giving me 8hm.
Also changed 680pf cap to wima the 33pf caps are silver mica and 0.1uf caps are jantzon.
Transformer buzz when I conect speaker and I have to turn amp on first or speaker protection kicks in.
It must be something I have got wrong but all components are as printed on pcbs and both pcbs do exact same fault.
I get 0.8v dc with speaker conected and 1.5v dc with no speakers conected.
Things I have tried is removing soft start ,speaker protection and fan pcb all at same time so it was just running on power supply.
Still exactly same dc at speaker readings.
I can get dc to go up by adjusting pot to 2.8v but it wont any lower than 0.8v.
Speakers are 4 ohm wired in series giving me 8hm.
Also changed 680pf cap to wima the 33pf caps are silver mica and 0.1uf caps are jantzon.
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Thank you again for helpng me I get - 2.5v at wiper pot +48v side
Sorry for sounding stupid what part is cathode
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Think I have worked out cathode voltage at 4k75 resitor wiper pot side and is -6.2v
Also I checked some voltages without speakers conected I get +47.7v & -47.7v
With speakers conected I get +46.0v & -46.3v
Ksa 601 pcb top MJ21193G 0.5R resistor I get 215mv
Bottom MJ21193G 0.5R resistor I get 229mv
Ksa 602 pcb top mj21194G I get 229mv
Bottom mj21194G I get 257mv.
Should they all be the same
Thanks neychi I run it for about 2 hours playing music and checked temperatures hottest places was 59c at edge of back of transistors.
I have to use 2 4ohm speakers to get 8ohm or tranformer buzzes and speaker protection kicks in.
Its strange how I have got exactly the same dc voltages and faults on both boards.
This is where your fault is.
If the pot is set to centre position the wiper should read 0V (meter black lead connected to 0V).
Refering to the pic, D1 & D2 each drop about 1V, the diodes centre connection is nailed to 0V; looking at the divider chain (2x 4K7 + 5K pot) across the diodes, the pot is aprox 1/3 of the total resistance - meaning that the pot wiper will see 1/3 of 2V or -0.66V to +0.66V (roughly).
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Thanks itsmee so do I just need to adjust my dc pot to centre position.
At moment ive got it set to anti clockwise position until it clicks because turning it up seemed to turn dc up at speakers.
If I turn my pot it just makes dc worse -0.8v is the best I can get it as it goes up to - 1.8v.
My resistors are 4k75 I have double checked them with my meter pot is a bournes 5k pot.
Am I missing something and thank you so much for your time and help.
Centre pin of 5k pot goes to through a 20k resistor on a circuit that goes to pin 1 of 2sc2240 transistor pin 3 of 2sa970 transistor also coming of that circuit is a resistor 12k1 in series with another transistor 25R5 from B- and also a 475R resistor going to + side of 1000uf cap.
I have tested all resistors with a meter and they seem fine.
I have already replace 2sc2240 and 2sa970 transistors any ideas please what to test or the most logical part it may be.
Hi decan the first pairs I suspect was fake but my new pairs are not 2sc2240 / 2sa970 substituted with alternative ksc1845 /ksa992 transistors these are from rs components.
Thanks itsmee I removed the leg of 20k resistor at pot side conected it to 0v and get -3v at pot