Sansui 7070 questions.

warriorfan

Well-Known Member
Eatly fathers day gift came in the form of a 1978 sansui 7070. Work on the golf course has me just swamped so I no longer have time to troll the classifieds for dealspretty good deal on this unit as it was known to have dropped a channel 30 years ago. The owner put it up in the closet. So...Very minty but a bad channel. No haggle over the price needless to say.

Just kind of fiddling until I have some time to actually measure bias and offset. It has got one good.cleaning with deoxit. Most all lights work upon hitting the power button and the relay does click after 5 seconds or so. Hooked a test speaker up to find I actually have no sound from any channel. I tried only aux, am, and fm as sources. Meters for fm signal all function. I did a pretty thorough check for burnt wires, resistors, and bulging or leaky caps. No bad solder joints or cracked boards in this going over either. Could have missed something but it will show when I really dig in. Everything is very clean inside btw. I did notice a few things. I was noticing that the left and right side of the tuner dial indicator does not light up. A gentle tap gets the left side, but the right side will not come on unless I push lightly up on the connection for the lights where they plug into the board. When a do this I also hear a slight click sound that I will ha e to check once again but swore it was the relay. Wondering if the relay is not closing all the way? Hope I can get back to it this afternoon sometime. I was hoping maybe someone would chime in and.maybe this is a simple fix. Optimistic yet but surely those fused resistors are going to have me doing some work? Nice to see this has been covered at length here and this.looks like it will actually be a easy unit to work on. Kind of excited to see how this will compare to my au555a. Thoughts? Thx fellas!
 

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Well already have a problem in just trying to measure dc offset.

I set up to measure the right channel. Meter set to dc mV. Power off and hooked up my probes. Set selector to channel a, volume down, input to aux with no source conected. Push power button and my meter pegs. Relay is then heard after normal time of 5 seconds or so and my meter then falls to zero. I am using a meter with a sweep btw.

This kind of threw my game plan off. Went in with somewhat a plan and now not sure what is going on. Relay issue?
 
Anyone? I am kind of stuck. Not wanting to turn these trim pots if there is.something else I need to look into first. Thx
 
This unit was purchased new by the P.O. I have asked him a few questions since I got it home. Asked if anyone had been in it and he said no. Reason I asked is because the metal cover over the driver board was loose and had no screws in it. I also noticed this has a 2624 driver board in it. Should be a 2625. Owner said this was a floor model. All the plastic ties are in place and I see no sign it has been repaired in any way. If a floor model the guy that worked on it was most likely good so it could have been fixed before? Is this driver board correct in maybe being a revised unit?
 
You really need someone who has worked on one or more 7070's to advise you. It seems like you have a really nice unit (little used). Unfortunately I have never seen or worked on a 7070 - as receivers are quite rare in the UK.

This time of year is fairly quite on AK - it seems like the people you need are not around, best to wait for some advice (if you can!) rather than diving in when you have unanswered questions (driver board?) and maybe doing more harm than good. ;)

Good luck with it.
 
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Thx hyperion! This unit is in very nice shape short of it not singing like she should. It came with a fold up brochure, owners manual, and a large fold up schematic to boot. I am reading, reading, and more reading on here and other sights before I do much. I am not comfortable measuring bias before the speaker outputs so I have resigned to just reading for now. The power switch in this is kind of cocked sideways and I am seeing some power switch issues in my research too. Being a demo unit this piece has surely been turned on and off a lot. I have grown very fond of my au555a and I hope to see how this compares. I won't get silly and wrap fuses in foil or anything crazy. Heck I am pleased I can check out and know a little more than I did a year ago when working on this stuff. That's all owed to Audiokarma and the folks here. I have a few projects sitting and some threads that could use updating as well. 8U baseball and a darn golf course with pvc irrigation pipe tend to take the.majority of my time. Love it but I do have other loves. The picture is my office most days. And some of the goal of eye appeal we bist our ass for.
 

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A gentle tap gets the left side, but the right side will not come on unless I push lightly up on the connection for the lights where they plug into the board.
The lamps probably have cold solder connections on the lamp clips ( fuse style lamps)
 
Check / reflow connections on and within the protect circuit and relay. Relay and fusible resistors frequently have poor solder connections within the protect circuit.
 
Self teaching through only reading is fun! Lol. The driver board is 2624 and the power supply is 2625! Not being able to get a proper check of dc offset to me has to say the the initial problem is in the the power supply. Bottm cover off again with the schematic in front of me and BAM! No jumper wires in the schematic! Once I get some better lighting I will post up what has been jumped. It's two poles of the relay to one of the male end of the molex connectors from what I think I am seeing. Getting somewhere slowly but surely!
 
Check your switch settings ie. tape monitor

You mean speaker set A. perhaps ?
Switch setting was on source setting. And yes I had my probes and selector set to the speaker set A. I had a darn good thread open that could walk a dummy like me through check both offset and bias. It was also 7070 specific.

Rhx too btw. There are some questionable looking solder joints on the protection circuit, in particular on that black jumper wire. It doesn't look so much raised up like I would consider a bad joint but it doesn't flow into the board like the others if that makes sense. I have seen just a few bad solder joints on circuit boards and on those i could actually see the joint move. I will fire the iron up tomorrow! Finally going to subscribe tonight too!
 
in particular on that black jumper wire. It doesn't look so much raised up like I would consider a bad joint but it doesn't flow into the board like the others
Heavily oxidated solder connection does like to flow or even melt. Ohm out that connection and see if you even have continuity across the connection.
 
Cant get the relay cover off so it will have to wait until tomorrow. The connection on this black wire jumps to two points on the relay and has a plastic sleeve over part of it. The joints there are the suspect ones. On one you can actually see the hole in the board. I have continuity across all points on the bottom side but that just tells me that wire in the plastic sleeve is good still. I will have solid info tomorrow. Sure hope you guys can pardon how us newbs aren't quite as squared away on this stuff as most here. If this wasn't half ass fun and interesting I sure as heck wouldn't even be doing it. Thx for keeping it fun for me and offering your time up in the help and advice.
 
Also never been in a 7070 but the other larger xoxo's yes.
Back to checking offset, as Dave pointed out you need to have your meter set to dc volts (not mv) when first checking dc offset.
Note--- the relay prevents dc from hitting the speaker outputs until things settle down, often you will see a stray dc voltage as the unit powers up however (usually) they are of a very low amperage and not relevant.
Need to make a dim bulb tester before something unhappy happens.
Once you report back on dc readings we will continue.
First thing that comes to mind is the fusible resistors on the f2624 board have drifted high z which will pretty much shut the unit down until replaced.
Also take heed, the solder pads on that board are VERY fragile.
Also worth a mention that if you remove that board be very very mindfull to put it back correctly on its pins as it can be put back incorrectly which then causes more angst on the owner's part as magic smoke starts to pour out the top :)

-Lee
 
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