My 7070 Suddenly has no sound

I have a 7070 that all of a sudden stopped putting out any sound from any of the speaker channels. I have checked two fuses I could find inside and they are good. I also tried other speakers.

The tuner seems to still be getting a signal just no sound.

What should I check or where should I send it for repair?

Do you hear the relay click a few seconds after power up?

Were you listening to it when it quit, or did you turn it on and nothing?

Rob

This unit has fusistors in the power supply that go bad and then the unit won't work. Do you have a DMM?

Rob, No click after power up. I was listening to it through aux with the tv on at first it was working then I noticed the only sound was from the tv. So I didn't noTice at first that it went out. I do have a dmm but the unit powers up so would you still think the link in the outer supply could be open? King

That's what was wrong with mine

Did yours still power up, but no sound?

Yes powered on no sound. Pull the service manual off the internet and check 4-1 section 4, F-2625 board. The fuse resistors are indicated in the parts list, Fuse R is their designation. Check them with the DMM set to ohms, 3 x 4.7 ohm 1 x 100 ohm, there are also fuses on that board to check as well.

I'll see if I can find a service manual. If so I hope it makes sense to me looking at the schematic.

No need to read the schematic, just check the resistors with a meter

Main Board

So am I looking at R-03?

F-2526
R-21,22,23,24,29 4.7 ohm 1/2 watt EXCEPT 22-3-4 3 watt
R-03 I see on the silk screen BUT not on the schematic…. ( I have a bad copy )
R-04 100 ohm 1/2 watt
R-09 10 ohm 1/4 watt
Verify R-27 & 28 1 ohm 1/2 watt
R-17,18,19,20 .33 5 watt

F-2626
R-13,14 560 3 watt
R-04 22 ohm 1/2 watt
R-10,11,12 680 ohm 1/2 watt

If all this checks out AND you have a DBT .. then it's onto measuring supply outputs

I don't see R-27,R-28 in the schematic I posted. It says section 2A, but heck if i see it.
I may just need to send it to someone for repair.

Concentrate on what you do see vs what you don't- sansui and other manufacturers made changes to boards and omitted parts as production went on. Measure the others you can find and post your findings.

I have had no time to look into fixing this and frankly I don't know what I'm doing. Can anyone recommend a good tech to me?

Need a location.

bktheking said:

Need a location.

Click to expand...

I'm in Oklahoma City. But I'll send it where i have to to get this back up and running. Spring is here and this is the stereo for my shop. we have no yard/pool music and that is NO BUENO!

Pm robisme

Will Do Thank you!

repairing the unit

Hi everyone, I'm an audiophile and electronic repairman, in the OKC area and OP found me on craigslist trying to sell another sansui(qrx-9001) that I had restored and modified. We have been e-mailing back and forth, and I am going to start the repairs next week hopefully. I will be back to post pictures and fixes.

began work today

So today I began working on this 7070. It was a little dusty from on the interior so I used my magical shop van attachments to clean up the case and the interior. I didn't use any electronics cleaner or deoxit yet I wanted to verify the problems the unit was having as described earlier(powers on, no audio though left or right channel, tunes appropriately to frequencies and indicates when an fm stereo signal has been reached).

Tested unit, tuning seems functional as in it will dial in and fm stereo will light up so I am going to ignore that board for now. We have power, the unit powers on and supplies voltage to the lights, however the protection relay doesn't click on so I assume there is some dirty DC voltage on the main supply board.

F-2625
The main power board relay did not click on so I suspect there are issues with caps and resistors on the main board. Specifically, the fuse able resistors on the main board have mostly turned white to indicate rupture. also Capacitors C07, and C08 look swollen with the wrapping split on c08 and I suspect may have caused the fuse resistors to blow in the first place. There is also a broken diode (10D) on the main board which shows resistance in both directions. I need to find a replacement part number for this diode. I know it is a common diode and I need to search for the replacement but I was hoping someone will come along and give me the part number. Im pretty sure radio shack still carries them.

F-2624
On inspection there were mostly blown fuse able resistors which I have ordered replacements for.

My first steps to check the driver circuit adjustment checks. Each channel on A and B read at around 4.00 V DC that was unchanged with adjustment to VR-01 and VR-02. The Bias current read a little high on both channels but where adjusted back to 30mA through VR04, VR04. I have also note the ZD01 and ZD02- (24v 1/2 W ZD's) had some odd black corrosion along the leads and needed replacing, those have been ordered.

F-2626

The power supply gave some crazy readings (Unpowered, aux from top four,
1. 1.49 2k and rising.
2. 8.9 20K and rising.
3. 10 20k and rising.
4. 12 20K and rising.)

I have ordered replacement resistors for the fuseable resistors for the board. The zener diode had some odd corrosion so I ordered a replacement for that as well (13v 1/2W ZD's).

There are no obvious burns to the circuit boards and I believe the passive replacements will suffice to bring this unit back into service. Once I have the components in the mail I will replace the caps, resistors, and diodes.

I am going to post some pictures to show you the work I am describing.