restoring old stereo

[bluesky4us]

finishing replacing most of the transistors on a HH scott 325 R receiver.
i dont really know what to do if the bias adjustment pot is destroyed. i know that you replace it with the same exact one but where are you supposed to set it to prevent another burn out.

 

[cbenda]

Look for information at HiFi Engine; http/www.hifiengine.com.

 

[bluesky4us]

i have all of the papers.
one pot is set right where it is supposed to be i wrote down the resistance and ordered multi turn pots.
i when i am done i will follow the instructions and correct the bias.
the last owner turn the original pot the in extreme position and it burned out. it is to bad that i got something that needs so much work done.

 

[cbenda]

Make sure the multi turn pot can dissipate the heat. Single turn have higher dissipation ratings. The designer probably used 1/2 to 3/4 turn to get maximum dissipation. I didn't see the exact model, but found a near model (320R) that recommended 40 ma. In the HH Scott 320 the bias pot is 330 ohm. If used at 150 ohm with a 1.2 volt drop the dissipation would be 1/100w. Not much. 10x that would be 1/10w and plenty safe. I must be thinking of tube bias where the pot is in the cathode. Make sure to change the electrolytics that look swollen as well. Good luck.

 

[bluesky4us]

i finally the bias is repaired but i am having problems with a 220ohm resistor shorting out and burning in the circuit.
the 320R has the same typology for resistors i am lost on what to look at next.
first thing i tried was using to ohm meter to check for the short no luck.
next thing was checking the leakage of all transistors in the circuit. in fact i checked the whole board again no luck