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Sansui 771

Eagle1

Eagle1

Super Member
I aquired this babe from Goat67 who got it as a freebie. It was very dirty inside and out, lots of scars and pealing vineer on the wood cover. None of the dial bulbs worked nor the FM stereo signal indicator. After a throrough cleaning and deoxit/faderlube, bulb replacement, and adjusting the idle and bias to within spec tolerance, it's now operational! The SM for this is quite good compared to what I've found for the Sansui 5000 series. I'm now running it through it's paces hooked up to a pair of Pioneer HPM-100's and functions work as they should. Alan Parsons LP is currently playing and at 40 WPC sounds damn good with the HPM-100's.

Quote from sake from the 5000A thread:
Hey Eagle1,
I also have a 771. I attempted to measure the bias on it, but couldn't get a reading. I measured across the -+ @ F01 after removing the fuse like it states on page six of the SM. Any tips?
sake

Hopefully you've set you DMM at mA not mV. If you're using an analog meter it might not read that low. Remember you're checking milliamps not millivolts so make sure you set your meter accordingly on this check. Also the pots are very sensitive so it doesn't take a hair to get within spec. Then let it settle in before as per the SM before you try again so it stabilizes. Your looking for 19 mA +- 1mA. Lot's of freedom there.
 
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Eagle1 said:
Quote from sake from the 5000A thread:
Hey Eagle1,
I also have a 771. I attempted to measure the bias on it, but couldn't get a reading. I measured across the -+ @ F01 after removing the fuse like it states on page six of the SM. Any tips?
sake

Hopefully you've set you DMM at mA not mV. If you're using an analog meter it might not read that low. Remember you're checking milliamps not millivolts so make sure you set your meter accordingly on this check. Also the pots are very sensitive so it doesn't take a hair to get within spec. Then let it settle in before as per the SM before you try again so it stabilizes. Your looking for 19 mA +- 1mA. Lot's of freedom there.
Click to expand...

Well, this was a while back when I tried it. I remember setting the DC within spec and then tried the bias. From what I recall, I was never able to get a reading on the DMM so I never touched the pots. I'm listening to it as I type and it has alway run cool but I would like it to be within spec. I'll give it another try when I slide the 5000a into its place.

Something else I've wondered about the 771 is the actual WPC? I've heard 40, 45 and also 32 per the spec sheet here: http://www.classicsansui.net/images/Literature/Receivers/771/771d.jpg . Which is it? :scratch2:

sake
 
Testing DC offset and bias is done with the meter set to millivolts. I believe with it set at milliamps you can cause damage. Please check this before you start.
 
Yikes! I don't wanna do any damage. Could this be another misprinted SM?
 

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No, those specs are correct. DC offset is always mV. A lot of Sansui service manuals, like this one, show measuring bias current across the fuse. You need to have your meter set for current (mA) measurement and the value will be in milliamps. To measure current, you need to change lead positions on most meters.
 
Make sure you take out the fuse, as the picture in the SM shows. Ammeters can't read in parallel, so you have to put it in series with the circuit. Just thinking that it could be the issue....
 
sake said:
Yikes! I don't wanna do any damage. Could this be another misprinted SM?
Click to expand...
No misprint in the SM, sake. You need to pull F01 to check bias for the the left channel and adjust VR03. Let it stabilize and adjust if necessary. Then reinstall the fuse and then remove F02 for the right and adjust VR04. If you lucky and have 2 DMM's pull them both and hook the meters to the fuse terminals watching polarity per the schematic that you posted. The pots are very finicky so it doesn't take much movement and don't panic. There's no real center point to them and if you over do it the relay should protect. Remember no speakers are hooked up while performing idle (0mV) or bias tests (no load).

As for the question about WPC the SM lists it as 40w both channels driven @ 1,000hz, 32w at 20,000hz at 8 ohms. I'd have to say it's under rated so more like 40 wpc as my HPM 100's perform nicely, but I bet my HPM-60's would like it even better.
 
I opened my 771 to adjust the bias & got no reading again. I have no idea what I'm doing wrong but I get -0.00mA on my DMM. I followed everything to a tee. I have used the same DMM on an HK 380i recently and that went as it should. I'm stumped.
 
Be sure you have the leads plugged into the correct terminals and check that the meter is set correctly. If so, then check the fuse in your DMM. You may have popped it.

- Pete
 
Once again I learn something here at AK. As far as amp readings, LBPete is on the money. Many meters require a move of the probes into a different port for the taking of amperage readings. Check your meter. Good luck with your readings and adjustments.
 
LBPete said:
Be sure you have the leads plugged into the correct terminals and check that the meter is set correctly. If so, then check the fuse in your DMM. You may have popped it.

- Pete
Click to expand...

*Update*

Pete,

You nailed it with the DMM fuse, I replaced it and got my readings. Both channels are now @ 19mA. Thanks guys.

sake
 
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