Discussion in 'Exclusively Sansui' started by Young46, Oct 10, 2017.
Photos of the measurement from one transistor to the other on right channel.
touch your meters probes together and deduct what you see as the readings .
You should be measuring 4.7-5Ω from the EMITTER of the driver, to the BASE of the corresponding output transistor.
Pictures help, like for example, I don't know why you are getting this reading, a picture can show us where you are measuring just to confirm.
Should be reading higher than that Pete, should be about 5Ω
In your first picture, it looks like you are on the centre Pin of that driver, you should be on the right hand pin of the driver...
i am looking at it a different way yet again .. please carry on .. sorry for the interruption .. best me not bring more variables in to play
was trying to figure the good parts from the misreading ..
I'll run out and check it again. While I am doing that, attached is the same photo with some added text.
Here are new photos. Same reading. I was pretty sure I had it on the emitter or the driver but didn't hurt to re-check.
Okay, thats not right, so now we have to start eliminating.
You have to now find the BASE resistors for the output transistors, they are on the F2980 board near the emitter resistors, they will be those bluish ones with the S bends on the legs. They are 1/2 Watt. The manual states 4.7Ω, but who knows with these Sansui's, they may have changed them. Locate those and measure them, I do not think the schematic is correct for the identification numbers.
You an measure from the end closest the output transistors, to the BASE of the corresponding output transistor, you should get something like 0.2-0.4Ω, in other-words, a direct connection.
then from the other end of the resistor back to the EMITTER of the driver transistor.
So we need three readings. Surrounding the BASE resistors.
1, the resistor Ω
2, Resistor to Output BASE.
3, Resistor to Driver EMITTER.
Okay. I need to reiterate that this receiver has been worked on before I got it. I’ve stated that in earlier post but don’t know if it has been lost in the shuffle. I will check them and report my findings. Thank you
Please don't take this to mean I'm being argumentative. I am a bit confused and want to get it right so please look at this and give me some guidance. The resistors near the emitter resistors are R60 (2.2Ω), R82 (1Ω), R04 (1Ω), R66 (2Ω), R52 (220Ω), and R54 (220Ω). I'm taking the resistors you are referring to are R60, and R66. Nowhere in the area are there 4.7Ω resistors. I am attaching some marked up sheets from the s/m. I replaced R60 and R66 because R60 was reading 214Ω. Maybe I should not have, but I did. I checked them first against the s/m, measuring the actual resistors (R66 was ok but I replaced it anyway so as the match R60. I also looked up the value according to the banding on the resistor. Are R60, and R66 the resistors you are referring to and where I should be taking the measurements?
Missed this attachment.
Okay, thats fine, so this means the last measurements you gave us agree with the 2.2Ω Base resistors that Sansui seem to have put in place of the 4.7Ω they show in the schematic I was looking at.
This sort of thing is common with Sansui so lets move on. Everything is fine.
What we can conclude from the last few measurements I had you make, is that this amplifier should work and you should be able to apply some Bias current to it.
Turn the unit on connected to the DBT, and measure across an emitter resistor, and start winding in some bias current.
Do not worry about the DC offset at this stage.
Bias adjustment readings
sorry for butting in again ..what are voltages across r72 r78 . two readings ..
You should be able to adjust that down, you should be starting with the trimmer all the way ANTICLOCKWISE.
Never start with the Bias trimmer in the middle.
Only start the DC offset with the trimmer in the middle.
He has 100Ω emitter resistors in there at the moment. That is why the voltage is that high.
What you have there is 290mA of current, you need to adjust it down, way down....
I would like to see you be able to adjust it down to about 3VDC
ah ..i missed that bit .. even so knowing each voltage to see if a relative match isnt a bad idea to see ,.
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