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Sansui solid state 7000 repair, recap, and restore

Quick question for you Doug or anyone else for that matter.

I have another thread "https://audiokarma.org/forums/index.php?threads/help-with-a-sansui-7000.909035/#post-13653273" where I am troubleshooting an issue with a Sansui 7000.

I have ordered a bunch of cap's and small transistors, but before I started the replacement this morning I measured the VR (Pots) again to see if one of them could be my issue (Right channel all but gone, very little sound, but when using Mains IN everything sounds great).

Low and Behold, VR704 the other half of VR703 - Volume pot's measure differently. These are 2 (double) gang pot's connected to a single volume bar. VR704 - measures from about 1.8ohm up to about 35Kohm, and then back to 1ohm as you turn the bar (measuring Resistance from Center pot connection to either right or left side). The other part of this VR703, Measures 1.6Ohm up to about 65Kohm as you turn, while the other side measures 65Kohm to 2.0 ohm as you move(Inversely).

QUESTION - After cleaning about 50 times, no difference. Is VR704 for the Right Channel? Has anyone seen this? I have the (I believe it is the Muting) wire attached to the top of the Pot for VR704 removed. Is there a matching replacement?

Ok so that is more than 1 question. Thanks in advance!

Andy
Picture attached if you need to see it. Pot_VR704_VR703.jpg
 
Its not unusual for volume and other control pots to track unevenly.
I tend to doubt that's your issue.
I do suggest troubleshooting before you start changing pieces.
You can inadvertantly create a secondary problem.
Look for low hanging fruit first. You say main in works fine. That means the power amp section is working. So you know its before PA.
That said, I'm unfamiliar with this unit. Is there a separate/ connected switch?. It could be dirty.
Are there preamp out, amp in jacks?
Jumpers could be bad or connections dirty. Also tape monitor switch contacts and any , all controls (balance, bass, treble.....)
One of the beauties of troubleshooting stereo gear with one channel out is, you a a working example of what should be happening for comparison.
Go slow, double check your readings. Let us know what you find.
Once you get the bugs out. Only change components, one board at a time then retest. That way if you make a mistake, you know where to look. Good luck!
 
oh ps, did you check the pot readings you described out of circuit?
The pot might be on and something nearby could be causing discrepancy.
 
aspisa said:
VR704 the other half of VR703
Click to expand...

They should not measure differently. This indicates a problem.

aspisa said:
one measures about 35Kohm and the other about 65Kohm
Click to expand...

Ok, this is a red flag, too. Both of these should measure 250K. You are measuring these pots after removing them from the circuit board, right? If not, then the readings are not useful and you'll need to pul them out to measure them.
 
I knew you were going to say that! I should have done that already, I just found it REALLY strange that one set of leads from the same POT go from 2ohm (or thereabouts) to 65K (or Vice Versa) , and the other go from 2ohm up to 35K then back to 2ohm, on the same leads.

Pulling that part out, didn't mean to hijack your thread..

Are you still refurbishing your 7000?


Thanks
Andy
 
OK after another day of playing, I have determined that the POT as noted above is fine, out of circuit it measures fine. I also found that rotating the Balance pot affects the volume POT VR703,704 in the manner I measured. Meaning if the Balance POT is turned one way the behavior moves from VR704 to VR703. So I guess that is expected.

I think it is time to just start replacing the Electrolytic Caps and the small Transistors on the board. I REALLY wanted to find the bad part before doing this so I know I am not adding problems.
 
aspisa said:
OK after another day of playing, I have determined that the POT as noted above is fine, out of circuit it measures fine. I also found that rotating the Balance pot affects the volume POT VR703,704 in the manner I measured. Meaning if the Balance POT is turned one way the behavior moves from VR704 to VR703. So I guess that is expected.

I think it is time to just start replacing the Electrolytic Caps and the small Transistors on the board. I REALLY wanted to find the bad part before doing this so I know I am not adding problems.
Click to expand...

One reasonable path forward would be to lift one leg of every two-legged component on that board so you can test it "out of circuit" without actually taking it all the way out of the circuit. It can be faster and less risky to 50% of your solder pads this way. You'd be looking for shorts, for opens, and for more-than-10%-off values.

You could also measure the known voltages from the schematic on the in-use, turned-on board and look for more-than-10% differences. Those would indicate not the component that is bad, but the *area* in which a component might be bad.

You're getting in deep on your unit, so I'd recommend you start your own thread and you'll get plenty of AK advice specific to your problem.
 
Old thread, but....
What an outstanding presentation on the rebuild.
Thinking about bringing one back to life, and this thread answers all questions.
dlucy Awesome job
 
Totally agree , great thread and great job!!!
I read all the thread good school!
Thank you Dlucy for shared your knowledges.
 
Hello Fellow AKers. Um, after a rotator cuff surgery on my left shoulder, I do not think I will have a soldering iron in my main hand for Year or so . I am lol king for a person do do a recap)rebuild on a 7000. It works well, but I can tell at least one of the original Elna caps fried. So looking for options on who has time to take on a project , for a reasonable price.
Pat b. audiogeek58@gmail.com us my contact info. Will ship with custom packing . 6124147528 is also contact. Anyone interested. Thank you Pat Beaudry, minnesota
 
@dlucy

Thanks for this info, it seems our paths cross again. I am restoring a 7000, however as you pointed out there are two revisions, all of data appears to be related to the first run (larger tone board). The unit I have is a later run and has the smaller tone board, as well as different phono / filter board.

All the service manuals I found on the net seem to be for the first run. Discouraged as Sansui is well known for undocumented production changes, I took a look at the service manual that came with the unit and believe it or not they did updated it to match the new boards. You can see the difference in photos on Page 9 of the old / new one.

As this manual does not seem to exist on the net I have scanned the service manual + schematic and uploaded it to HiFi Engine, not sure if it will make it there (maybe they wont catch the difference). I wanted to upload it to AudioKarma's PDF database but my account wont log in and there is no register button.

I've uploaded it here but I don't know how long it will stay up for long (free trial account).

https://www.mediafire.com/file/72wnc7i0wfym1yt/Sansui_7000_New_Revision_service_manual.pdf/file

From here: https://www.audiokarma.org/forums/index.php?threads/sansui-7000-a-tale-of-two-bothers.369638/

DCinDC said:
The tone board is totally different and they have different filter and or protection boards.

SN 222110187 this is the newer one with the smaller tone board in the pics
has a tone board marked F-6010
has a power filter board marked F-6012
has a phono board marked F-6011
These numbers are not even in the board db and the number is so high you'd think it was either a service replacement or from a much newer unit!

SN 221030054 this is the 54th one made! and has the big board in the pics
has a tone board marked F-1316 this one has had lots of mods with cut traces and jumper wires.
has a power filter board marked F-1317
phono board preamp is incorporated into the tone board.
Click to expand...

Also, can you comment on how you mounted the new bridge rectifier? It seems that its meant to be through hole mounted but the one that is in here is mounted via screws.

This is what you used correct? https://www.mouser.com/ProductDetail/Rectron/BR84?qs=/ha2pyFaduhoYoY1QPDl2HeEhsNu8PPMhycZN02wwSU=
 
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perryinva said:
Ok, How does one replace the indicator bulbs? The dial fuse bulbs and pointer bulb are o vious and well documented but the FM-AM-Phono bulbs look they should just pull strait out from where the wires can be seen on the inside. Mine don’t budge! Is there a trick to it? The rest of. my restore is going nicely.

BTW, NOW I know why the unit was switched to low power. For the average user, that gives you some actual range of gain adjustment. Dear lord, talk about your non linear volume pot! The amp is near full power at like 5 on the knob switched to full power! I barely have it past 1 in normal use!

Also, something I haven’t seen mentioned, there is an actual top and bottom on the pushbuttons. The front of each button is sloped a bit. I pulled off all the buttons to clean them and stick on my new labels and two were upside down and not noticed until on the receiver. Then I had to carefully peel them off and reattach them!

Thanks for the BOM, dlucy, it was a good start. Mine has the separate phono board and smaller tone board so all the transistors are different. A few C632AY71 and NEC A640 2L11, which I haven't found a cross for. The Power Protection board is also different, mine as more caps, but mostly the same components. I already had all the common capacitors. Driver boards are identical.
Click to expand...
I know that this thread has some age now, where did you get the new labels for the buttons? I have the same issue with the buttons on my 7000. All but two are long gone.
 
Due to an international house move I've stopped the availability of the button label reproductions, but I do have stock and will make them available again, but it may be a few months or more until I'm settled.
 
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