My Sansui seven

Spectrum17

New Member
I recently purchased a pair of older Sansui receivers, an 881 and a Seven. The 881 responded well to a light cleaning and is currently in use. The Seven on the other hand needs some attention.

I've cleaned and lubed all the switches (which by the way have all their labels intact) an pots. It appears the pre-amp section is fine, as I can send the signals to an external amp it it sounds just fine. When I use the on board amp section I only get sound from the right side and only very faint. I'd like to know where I should start my investigation. I am only armed with a schematic and DVM. Is this something that I should attempt or take it in and have it serviced?

Thanks
 
If you don't have any experience poking around and measuring voltages on a powered up piece of electronics, it would be a pretty tall order to safely debug and fix without some pretty detailed help. But if you have some experience and/or knowledge, you could do some basic troubleshooting and see if the proper voltages are getting to the amp boards, etc.

You've already checked all fuses?
 
I've never been in a Seven but there are some common troubleshooting steps. is it in protection mode? There is a relay between the amp output and the speaker terminals. That relay opens if there is a serious fault in the amp. It may be as simple as dirty contacts in that relay. Aside from that, measure DC offset. Its generally done by measuring the DC voltage across the speaker terminals with the volume at zero. If it's in protection you need to find a point before the relay. Start there and report back.

Please post the serial number for the database. Click on the link in my signature block.

- Pete
 
I assume you've checked fuses on the back panel - they would take out one side in the power amp, but I don't think in the pre-amp. Assuming it is the power amp, you can swap the 2 driver boards that's underneath the metal screen - but be very careful when "undocking" the thermal transistor from the heat sink. If the fault stays the same it is not in the driver boards, if the fault moves to other side, then you are down to one board.
 
Thanks for the replies, I've entered the SNs into the database.
I'm comfortable poking around with a DVM on powered device, spent the first 13 years of my career doing just that (but mostly digital circuits)
fuses are fine
Relay is not in protection mode (that I know of, I do hear and see it engage about 2 seconds after power is turned on, and then I get some sound)
Tried swapping the driver boards, problem does not follow them
DC offset is 129mV on the left and -109mV on the right.
 
DC offset is high but you should be able to adjust it into specification. The Seven calls for connecting a dummy load across the speaker terminals to set/adjust DC offset. I don't suppose you have a 50w 8 ohm resistor handy? The trimmers are on the driver board. There are access holes in the bracket that holds the board in place.

If it's not in protection and you are not getting sound from the amp section, the signal is getting lost between the amp and the speaker terminals. Could be dirty relay contacts or a dirty speaker selection switch.

- Pete
 
Thanks for the response, have a dummy load resistor on order and the service manual dowloaded, going to adjust when it arrives.

Note: it's not that I get no sound at all, just one side and very faint. I'll be looking into the relay and see how it looks.
 
The cover comes off the relay but sometimes is a little tricky to get it released from the tabs on the base.

- Pete
 
Got the DC offset in spec, relay cleaned but now I must throw myself on my sword. The speakers fuses (while looking very much intact) are blown. I just gave them a glance and never put a meter to them as they looked fine. Now to find out what is taking them out. Sorry for the wild goose chase folks.

I'll go hang my head in shame for a while
 
Glad to see I'm not alone :) So, it will blow fuses only when the driver boards are installed. If they are removed the fuses are safe. (Which I suppose makes perfect sense)
 
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