Sansui G-5700 Restoration

She's alive and kicking again! I de-soldered both new output trans, and both driver trans, and checked them, they were all ok even after the second fuse blow. I finally got in a new 100 ohm trimmer today and popped it in, re-soldered all the transistors back in. I built a dim bulb tester yesterday for around 10 bucks. I had to buy 2, 75W bulbs rated at 53W each and a spliter to make to get it close to 100W. (new efficient bulbs these days). Then i was cleaning in the garage today and found a huge box of 100W old school bulbs that were still good, and used that instead :rolleyes:. I powered it all up and was expecting to see a bright bulb from the receiver still being shorted, but it wasn't!! Huge sigh of relief.... The 100 ohm bias trimmer must have been the last component causing the short. Not sure why, I checked the damaged trimmer again today and it was 300 ohms on one side, not open. All this stuff is crazy touchy. I spent forever checking everything on the board.
 

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Good work!! You were lucky to get away with that...!!
Remember with a DBT you can only use a incandescent light bulb.
Unless the trimmer was O/C, it would not cause an issue like that...
 
I was thinking maybe the ohms were so high on one side of the trimmer it was causing a huge voltage surge when turned on. I don't know though! But its working great again!
 
I noticed the display lighting is not quite as bright on one side because of the G-5700 only having one display bulb. It has the mount for a second bulb on the other side. I ordered a JKL 2964-8B lamp holder and sliced the one of the sides off to fit the cover on. I soldered wires directly to the output of the other lamp. Since I am using LED's the current draw is way less.
 

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I noticed the display lighting is not quite as bright on one side because of the G-5700 only having one display bulb. It has the mount for a second bulb on the other side. I ordered a JKL 2964-8B lamp holder and sliced the one of the sides off to fit the cover on. I soldered wires directly to the output of the other lamp. Since I am using LED's the current draw is way less.

I've done the same thing many times. I put green LEDs in a 3900Z (added one like you did), and a 7900Z and it gave it that "nostalgic" Sansui look.
 
She's alive and kicking again! I de-soldered both new output trans, and both driver trans, and checked them, they were all ok even after the second fuse blow. I finally got in a new 100 ohm trimmer today and popped it in, re-soldered all the transistors back in. I built a dim bulb tester yesterday for around 10 bucks. I had to buy 2, 75W bulbs rated at 53W each and a spliter to make to get it close to 100W. (new efficient bulbs these days). Then i was cleaning in the garage today and found a huge box of 100W old school bulbs that were still good, and used that instead :rolleyes:. I powered it all up and was expecting to see a bright bulb from the receiver still being shorted, but it wasn't!! Huge sigh of relief.... The 100 ohm bias trimmer must have been the last component causing the short. Not sure why, I checked the damaged trimmer again today and it was 300 ohms on one side, not open. All this stuff is crazy touchy. I spent forever checking everything on the board.

Well, a 100 ohm trimmer should not read over 100 ohm. What was probably happening was some oxidation or dirt is in the trimmer creating more resistance, which caused the BIAS current to be way high. As ghazzer and kevzep said, you were very lucky! These "new" halogen bulbs are still a resistive load, and still an "incandescent" bulb, but like you discovered, you need to watch the actual wattage draw, and thus voltage drop when using them. Thanks to our government telling us they know "what is best for you", real "standard" bulbs are illegal..:mad: I do have a stash of "rough service" 130v bulbs for future reference though. :biggrin:
 
I managed to buy a new M5540 display chip. It was not cheap. Got it installed along with a recap of the F-3000 board. It did not fix the Display issue!!! It is exactly the same as before missing the center tune dot and pointer. Not happy. Good thing I used a Socket. Something else is causing the issue.
 

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I managed to buy a new M5540 display chip. It was not cheap. Got it installed along with a recap of the F-3000 board. It did not fix the Display issue!!! It is exactly the same as before missing the center tune dot and pointer. Not happy. Good thing I used a Socket. Something else is causing the issue.
Quite likely needs an alignment, I'd say with that, the discriminator is off a bit...
 
The triangle arrow indicator is constantly on, the other never comes on, no matter if its in tune or not. Can I do this alignment with only a multimeter? I'm checking the service manual. There are 3 trimmers on the board itself.
 
I'm getting over 4V on pin 42 and 43 of the F-2988. Service manual says its supposed to be 0V
 
You really need and RF generator that can do frequency modulation with an audio tone and a distortion analyser.
But you can adjust the T02 for 0V between TP 42 and 43, it sounds like its off, you need an antistatic plastic or carbon-fibre adjustment tool, DO NOT put a metal screwdriver in the coil adjuster as you will break the slug and then you'll need a new T02 not to mention you'll throw off the adjustment just by you metal object and hand near the coil..
I would adjust it, it may bring it back, 4V offset is way out...
 
I adjusted T02, after 2 full turns either way the voltage was still over 4V. It would not go lower than 4 or higher than 5. I used a plastic screw driver.
 
I would look for a tech in your area who has the equipment, knowledge and experience to perform an alignment. I have a decent amount of all 3, but would never consider myself qualified to perform an alignment, even on my own gear.
 
Question: Other than "Receive the nearest FM station", are there any other conditions that must be set up before you measure for 0vdc ±0.2vdc between pins 42 & 43?

The F-3000 schematic shows that 15 & 17 (42 & 43 from F-2988) are normally at 5.6vdc and within ±0.1vdc of each other. (???)
 
You need to realise that some of the instructions in that tuner alignment are in fact completely inaccurate, I have had to devise my own method of aligning these tuners.

Basically it needs an alignment and it needs to be done by someone who knows what they are doing.
 
I adjusted T02, after 2 full turns either way the voltage was still over 4V. It would not go lower than 4 or higher than 5. I used a plastic screw driver.
Thinking a little more about this, perhaps someone has been in there fiddling about, you can never get that adjustment to a perfect "0V", but should get it to <200mV.
T01 will also affect this adjustment, but it will also affect discriminator alignment, it needs to go to an RF specialist who has the appropriate alignment gear.
 
I've started a project on one of these units. Got it from a friend that hasn't used it in years. He also gave me a 7700 to work on, but since it powers up I decided to start on this. Got a few ?'s.

This one appears to have had some work done on it. There are assorted "new" caps in different boards (Nich's instead of Elna's). It wouldn't power up when I got it. Upon opening, I discovered no main fuse (6A) on the PB, which led me to believe there would be issues. I put a 2A fuse in, plugged it in via DWB tester, turned it on & SNAP! Thought I blew the fuse but no.......fuse(s) all ok but bulb brightly lit. Quickly shut er down........can't find any obvious burnt/blown components.

First, having read through this & other threads on Sansui's, I will recap the PB & F3060 board, & replace the trimmers.

But I'd like to isolate the problem. Is there a quick/simple way to do that on these? Would removing the three 2A fuses be a good start? I hate to assume anything, but I would guess that if there was an issue on any of the boards powered by these that the fuse would do its job, so my guess would be an issue on the 2980. Fair assumption?

When recapping, do you guys replace all the disc caps too? I've read where most times these are reliable unless visibly damaged.

Would it behoove me to remove the 2980 board from the unit before doing the work? Or is it not worth the time? I've seen it mentioned to NOT do any unnecessary solder work on these boards.

Upon inspection, I can't see any bad joints on the bottom. I was expecting to find a few after what I've read about these.
 
Definitely a short somewhere. Get the right size fuse. 2A will blow no matter what... Keep it on the dim bulb till it goes dim.
I would start by probing the Main output transistors and drivers from each channel. Do continuity checks between E C B on them to see if there is a short, most likely there will be. Then set the Diode setting on your multimeter. Search google or here for the test procedure. NPN and PNP have different results. People say to take them out of circuit to test them properly, but you don't need too, to see if they are bad or not. Most of the time resistors will show physical damage if they are bad, but its easy to check them if they are open or showing a resistance. Maybe you'll be lucky and have one channel that works after disconnecting bad parts from the circuit. I had a shorted bias trimmer too.

I have never come across a bad ceramic capacitor, but I'm new... They shouldn't need replacing unless you want to improve the sound.
I never remove a board unless I have too. You should be able to loosen and move wires around.

After you figure out what is bad, then I would rebuild everything on that board. It has taken a lot of abuse and heat over the years. Way more than other's I have seen. Except the power supply board on the SX-1010 pioneer...that one is toasty...
 
Upon opening, I discovered no main fuse (6A) on the PB, which led me to believe there would be issues.
The fuse wont blow on the DBT, if you were on mains AC the fuse would blow.

You will have blown output transistors. NJW1302 and 3281 are the transistors you need to order.

When recapping, do you guys replace all the disc caps too?
No need to replace the film caps or ceramic caps.

Would it behoove me to remove the 2980 board from the unit before doing the work? Or is it not worth the time? I've seen it mentioned to NOT do any unnecessary solder work on these boards.
Not worth the effort, everything can be done to the F2980 in the unit. You can do as much soldering as you need to, you just need to be very careful, use proper solder extraction techniques when removing components and you will be fine.

You will need to remove and test your output transistors. Then check the emitter resistors. Then check the driver transistors.
The F2980 will need recapping and glue removed.
Bias and DC offset trimmers will need to be replaced.

But most of all, these amplifiers are terribly difficult to repair, so many things can go wrong, and it can be extremely frustrating for someone that lacks the experience, you need to be very patient.
I have lost count of the times someone comes here to fix one of these amps and then the thread goes cold, they either realise they are over their head, or they mess it up and toss it aside or in the trash...

Just things to consider....
 
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