DC Offset for Yamaha CR 2040
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merrylander
AK Member
Yes; First hook your meter across the +60 pin on either power amplifier board and adjust the variable resistor on the power board that is beside the regulator transistor with the square tubular heatsink for exactly 60 volts. You may have to remove the dial illumination strip to see it.
On each power amplifier circuit board locate two pins marked E and O. Connect your meter across those and adjust the variable resistor in the center for a reading of 0 volts.
Now connect your meter between pin O and the pin at the very end marked TP and adjust the other variable resistor (the one at the end) for 10mV.
Warm it up for about 5 - 6 minutes and check again, note that the volume control must be at 0 and no signal input present (select the phono input with the shorting plugs)
And do yourself a favor, if your meter has those honking big alligator clips get some mini-grabbers instead. Short any of those pins while taking these measurements and you will need a new set of outputs, fortunately there are sets of those flat pack Sankens that will sub nicely for the original Hitachis.
Rob
On each power amplifier circuit board locate two pins marked E and O. Connect your meter across those and adjust the variable resistor in the center for a reading of 0 volts.
Now connect your meter between pin O and the pin at the very end marked TP and adjust the other variable resistor (the one at the end) for 10mV.
Warm it up for about 5 - 6 minutes and check again, note that the volume control must be at 0 and no signal input present (select the phono input with the shorting plugs)
And do yourself a favor, if your meter has those honking big alligator clips get some mini-grabbers instead. Short any of those pins while taking these measurements and you will need a new set of outputs, fortunately there are sets of those flat pack Sankens that will sub nicely for the original Hitachis.
Rob
Puddintane
Super Member
Please forgive my reviving this very old thread, but it's exactly what I need. So it's easier than starting a new one.
I'm a total noob at this, and I'm hoping I can get a little handholding here as I attempt these adjustments. I have a Yamaha CR2040 that shows a high DC offset reading in the right channel (~150mV) and just a little in the left (~20mV, after it warms up and settles), as tested at the speaker terminals.
I also have done as Echowars has said here!
I ordered these from Digikey Sunday night, and they arrived via First Class Mail yesterday! I also have the service manual that I downloaded from Hifiengine.com. Okay, so on to the handholding.
Please allow me a few noob questions if I may.
Do I need to use a special pot adjuster for these adjustments (in other words, some kind of non-conductive tool)? And when I connect my meter for these tests, does it matter which lead is connected where (i.e., black to E, red to 0, etc.)? And how much do I turn these variable resistors (or trimpots, as I think they're also called)? Are they extremely sensitive or might they take several turns? And also, so that I don't blow up anything, which way do they need turned to reduce the offset? Is it the same as with other pots: clockwise to increase and vice versa to decrease? And last, for all these tests, I assume I'm to use the DC voltage range on my DMM. Correct?
Sorry for the noob questions, but my main goal--beyond learning how to do this correctly--is to not blow up anything!
Now to Merrylander's instructions. First, when you say to hook my meter across the +60 pin, do you mean the +60 and the -60, both of which are found on each of the main boards (l and r)? Or do you mean only the +60 on the left main board and the +60 on the right?
Second, there are two pins labeled E on each main board. There is one directly adjacent to the O pin (toward the front of the unit on the left main board, along with TP, -55, +55, and -60), and one in the back half (the arrangement is the same on the r main board, only reversed). Do I use these two pins that are adjacent to each other?
As always, thank you in advance for any and all help.
I'm a total noob at this, and I'm hoping I can get a little handholding here as I attempt these adjustments. I have a Yamaha CR2040 that shows a high DC offset reading in the right channel (~150mV) and just a little in the left (~20mV, after it warms up and settles), as tested at the speaker terminals.
I also have done as Echowars has said here!
I ordered these from Digikey Sunday night, and they arrived via First Class Mail yesterday! I also have the service manual that I downloaded from Hifiengine.com. Okay, so on to the handholding.
Please allow me a few noob questions if I may.
Do I need to use a special pot adjuster for these adjustments (in other words, some kind of non-conductive tool)? And when I connect my meter for these tests, does it matter which lead is connected where (i.e., black to E, red to 0, etc.)? And how much do I turn these variable resistors (or trimpots, as I think they're also called)? Are they extremely sensitive or might they take several turns? And also, so that I don't blow up anything, which way do they need turned to reduce the offset? Is it the same as with other pots: clockwise to increase and vice versa to decrease? And last, for all these tests, I assume I'm to use the DC voltage range on my DMM. Correct?
Sorry for the noob questions, but my main goal--beyond learning how to do this correctly--is to not blow up anything!
Now to Merrylander's instructions. First, when you say to hook my meter across the +60 pin, do you mean the +60 and the -60, both of which are found on each of the main boards (l and r)? Or do you mean only the +60 on the left main board and the +60 on the right?
Second, there are two pins labeled E on each main board. There is one directly adjacent to the O pin (toward the front of the unit on the left main board, along with TP, -55, +55, and -60), and one in the back half (the arrangement is the same on the r main board, only reversed). Do I use these two pins that are adjacent to each other?
As always, thank you in advance for any and all help.
merrylander
AK Member
Plus 60 with the red lead, black lead to chassis, with the other readings black to E red to O black to TP red to O.
Puddintane
Super Member
Post deleted--question already answered.
Last edited:
Puddintane
Super Member
One other question please, if I may. The service manual says to use 8ohm dummy load resistors at the speaker terminals. Is that a must? Because I don't have any of those.
merrylander
AK Member
Hook on a pair of bench speakers, not your best ones.
