Sansui G-5700 Restoration

Also, what is with the 2W(?) resistors tacked in parallel to the two 390Ω(5W) resistors for R605 & R606?
Just fine tuning the volt drop for that 12V regulator, to take a bit of pressure off the pass transistor I should think.
But actually 390Ω in parallel with 820Ω = ~264Ω ;)

(NB: to anyone seeing the 'quote' here - I did this manually ;) - current server problems prevent quoting).
 
Last edited:
Its a 13V Zener, do not replace it with a 1N4148.
They did this on the later revised F2980 boards.
 
As Kev says, I would not replace it unless it is bad. The fewer times that you heat up the solder & tracks the better. Once a track on these boards even thinks about lifting, you need to start running wire.

Do you have an oscilloscope?
 
Nope, don't have one.

Looks like C617 is causing the main issue. One leg was totally detached, I'm guessing from the glue and years of running.

I pulled C614 out and it is a 220uf 50V, But the schematic says 220uf 35V. All the other caps around there are 50-63V.... I'll have to order another. I only order enough parts for the job I am going to do to save costs.
 

Attachments

  • 20190117_132358.jpg
    20190117_132358.jpg
    54.5 KB · Views: 32
Last edited:
Timing is everything! I started my previous post about 3½ hours ago, but my wife was in a hurry to go to the grocery and I forgot to "send" it, til we got home.

After seeing what the previous owner/tech did to R605 & R606 (see end of post #19) I think you should take a careful look at everything on that board.

The F-2980 bd in my G-6700 has a 15K R614 standing up on the component side, between an R614 hole and what appears to be an added hole with tracks to TR601/C and TR603/C. Tonight I'll try to diagram the actual "as built" circuit and update my schematic.
 
It doesn't look like this receiver has even been touched. I'm assuming these were small changes made spur of the moment at the factory. I'm just going to keep it like it is. Good to know I have a later revised board.

I have not experienced any issues with the traces pulling up at all. I have replaced about 10 components so far.

Questions: C612 the 1000uf capacitor is 3 legged, I bought a 2 legged version is that ok, that it is not grounded?
 
Last edited:
It doesn't look like this receiver has even been touched. I'm assuming these were small changes made spur of the moment at the factory. I'm just going to keep it like it is. Good to know I have a later revised board.

I have not experienced any issues with the traces pulling up at all. I have replaced about 10 components so far.
I have already told you that you have the later revised F2980, are you reading our posts at all?
Nothing is done "spur of the moment", is a design development that would normally be accompanied by a service bulletin (or not)......
 
To me a later revised version would be a board revision, not just putting a diode in place of where a resistor is marked. That's why I assumed this was a change that was done before the board could be re-done.
 
Oh well, cool, you sound like you know all about it, I'll butt out, as you were, carry on.........
 
Sansui is well known for making design changes, or mods, and NOT updating their SMs. They may have release service bulletins, but I have never seen one.

So, no revision letter, P/N change, or whatever. You should always take LOTS of photos, and believe the configuration of the equipment you have in your hand rather than the schematic. One exception is when a PWA has obviously been resoldered or reworked. I do not believe that the reworked R605 & R606 was done at the factory.
 
Yeah I definitely am taking a lot of pictures!

Fun Times! So i managed to replace over 25 components today (on the power supply side) on the F-2980. I may power it up tomorrow and see if it works! ...and check the bias and channels.

So I am using my fluke meter in mV. Man it is really touchy, I'm assuming I have to hook up the grabbers and turn on the meter and let it sit till the meter Zero's out, to get a accurate reading. I have not replaced the trimmers yet, but I have Bourns ready to install.
 
She's alive! Safely operate, and FM stereo lights up now. All 4 speaker outputs have sound. Quartz lock does not. Does the center dot have to do with it lighting up?

So I checked the bias and after 2 min and it hit 3.3mV. Then at the 10 min mark it tops out at 6.5mv. The service manual says run the unit more than 3 min then adjust them. How much time should I let it run from dead cold, to adjusting them? Granted I have not changed out the trimmers yet, but I will soon. She looks rough, but I will get her in great shape! I have a lot more caps and transistors to do. Then it looks like i'll be working on the F-3000...
 

Attachments

  • 20190118_135743.jpg
    20190118_135743.jpg
    70.2 KB · Views: 22
She's alive! Safely operate, and FM stereo lights up now. All 4 speaker outputs have sound. Quartz lock does not. Does the center dot have to do with it lighting up?

So I checked the bias and after 2 min and it hit 3.3mV. Then at the 10 min mark it tops out at 6.5mv. The service manual says run the unit more than 3 min then adjust them. How much time should I let it run from dead cold, to adjusting them? Granted I have not changed out the trimmers yet, but I will soon. She looks rough, but I will get her in great shape! I have a lot more caps and transistors to do. Then it looks like i'll be working on the F-3000...
Turn it on, let it idle for 5-10 mins, set the Bias, then leave it, do not adjust it any further.

No quartz lock and no Dot is most likely a faulty 5540 chip.
People are going to tell you its caps, or the Crystal etc, but I have not found that to be the case in the literally dozens of these amps I have repaired and restored.
 
Thanks, I will figure it out and report back. I most likely will have to harvest a 5540 from a T-80.... sad. At least it's not critical to the receiver working.

Is it pretty typical that these old variable resistors are so far off on the bias when you find them to repair?
 
Last edited:
More likely that someone was mucking around trying to set it up, gave up, and left it wherever it was. 270° on the older single turn ~100Ω, or 10° ~4Ω. With a 25 turn trimmer 9,000° (25X360°) ~100Ω, or 10° ~0.111Ω. I would have much more faith in the long term stability of the new trimmers.
 
I also noticed when testing it out today that when FM mute is ON there is no sound at all through the dial. When Fm mute is off, its working correctly sound and fuzz.
 
I also noticed when testing it out today that when FM mute is ON there is no sound at all through the dial. When Fm mute is off, its working correctly sound and fuzz.

FM probably works off of the quartz lock system which won't be functional with the busted IC. I had an Onkyo with identical behavior and in that case fixing the automatic tuning functionality also fixed the muting problem.
 
I also noticed when testing it out today that when FM mute is ON there is no sound at all through the dial. When Fm mute is off, its working correctly sound and fuzz.
Around the Multiplex chip is a few Tantalum caps, I have found these to play havoc with the muting and cause distortion as well, they are hiding on the tuner board hidden by the F3000 board. It may or may not be the problem.
I would swap those out for some Electro's like Nichicon KZ KT or something like that....

Put the new trimmers in sooner rather than later, the slightest intermittent problem with a trimmer can put the amp in Chernobyl mode...
 
Back
Top Bottom