Sansui 7070 no output

[mars]

Hello Everyone,

I just picked up a Sansui 7070 from a friend. The unit is not in the best shape cosmetically but it can be cleaned and it should be OK. The problem is, no output. When I turn the unit on, the protection relay clicks in as it should. The panel lights come on as well as the function lights so I am getting power to unit. I have check the three (3) fuses located on the motherboard (Power Supply board) and they are OK. I have tested the FM and AUX section (connected a CD player to the AUX inputs) for output, nothing from the speakers. A quick DMM check of the power output transistors while they are still in the circuit are giving readings all over the place for resistance but again, I haven't disconnected the power transistors from the circuit so the readings are probably useless.
I have the factory service manual and schematics.
Any ideas on where to start would be greatly appreciated!

Best Regards,

mars

[aldena007]

I usually work on 9090's but the first thing to check is to see if the pre-out to power in jumpers are in place. These would be U-shaped bare metal jumpers on the back of the unit. If they are not there, then replace them or just use a rca patch cable in place of them for testing. If the jumper is there then your issue is with an internal problem on the power amp side. If you have another receiver, then you could patch from your 7070 pre outs to the other receiver's power in jacks. If your 7070 pre amp side is good you should hear output in the test receiver/amp. Also try the headphone jack. They usually are on the speaker circuit and will test out the power to the speakers. Headphones are actually speakers and inside usually some large resistors to provide a "dummy load" for the amp. If your headphones work, but the speakers dont' then you have a problem with the selector switch.

If nothing works, you do have a power amp problem, but both channels out means some real detective work.

Track down a manual at this point. You can't go into this phase without it.

[nosirrah]

Hello Everyone,

I just picked up a Sansui 7070 from a friend. The unit is not in the best shape cosmetically but it can be cleaned and it should be OK. The problem is, no output. When I turn the unit on, the protection relay clicks in as it should. The panel lights come on as well as the function lights so I am getting power to unit. I have check the three (3) fuses located on the motherboard (Power Supply board) and they are OK. I have tested the FM and AUX section (connected a CD player to the AUX inputs) for output, nothing from the speakers. A quick DMM check of the power output transistors while they are still in the circuit are giving readings all over the place for resistance but again, I haven't disconnected the power transistors from the circuit so the readings are probably useless.
I have the factory service manual and schematics.
Any ideas on where to start would be greatly appreciated!

Best Regards,

mars

I believe the 7070 has a recurring issue with cracks in the circuit board from the upright driver board hitting the case due to a clearance issue.
If you've checked the switchology, the jumpers are there in the back, and the fuses check good with a meter look closely at that board for cracked traces.
Pull the botton cover off for access, there are some threads here for details, use the search function.
The cracks are in the board that the driver board plugs in to, that main board that's horizontal on the bottom.
You can very carefully power it up with the case off, unit upside down, and using a plastic rod gently push down {that will be like up} on the main board.
Sometimes that will close the cracked trace and the unit will play.
Be careful...
Casey
Casey