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Sansui 990DB - no output -no tuner activity

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DaSpark

New Member
Hello Everybody,

I just received a Sansui 990DB (my company was about to trash it) along with a Sansui SR-626.

The problem I have now is that there is absolutly no output whatsover. In addition the tuner also does not pick up any Signal (or at least the meter wont show it).

It will go out of the protection mode (light turns green).

I have tried supplying the power amps directly with a signal from my phone. Also nothing

I have read a few threads already. I checked (as fas as I could) the Tuner Power Supply. As far as I can tell there is no Voltage arriving there.

I have checked all five fuses on the the main power supply board. They seem to be fine.

I am a bit at a loss at the moment. Any help would be greatly appreciated. What would be the best way forward? What to check next?

How do you measure the voltages on the main power supply board? It is quite hard to access anything. (Plus i am a little afraid that i might touch the main caps and get a shock :D).

Attached are a few pics.

Thank you and all the best from Vienna.

Ferdinand20200124_191141.jpg 20200124_191152.jpg 20200124_191202.jpg 20200124_191210.jpg 20200124_191231.jpg 20200124_191324.jpg 20200124_191348.jpg
 
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Check the two resistors next to the fuses that connect to the yellow transformer wires.

Also, there should voltage on the little tuner power supply pin next to that cap that is bent over.
12 volts I think. Wont be there though if those resistors are bad.

Had to look for this info. Resistors are 1 ohm 1/2 watt fusable resistors. I replaced them with fuses on an 8080DB I worked on years ago.

Rob
 
Last edited:
Thank you Rob,

These two resistors are definitely shot. Is it ok to replace them with 1 ohm 0.6 watt resistors?

Anything else I can check before going to the shop tomorrow to get the parts?

Thank you again for your quick help.
 
Buy a couple extra in case the new ones go. .6W should be fine, but they should probably be fusable resistors. If you can't get fusable, put in what you can get for now, and either order fusable resistors or install fuses. I mounted fuse holders and wired them in. Pics are gone in the thread I posted because of Photobucket.

Check the little power supply for bad solder connections for the transistor on the heat sink and the two large white resistors. Common for these solder joints to go bad.

Rob
 
Thank you Rob, will do.

Maybe a stupid question but how did you choose the correct dimensions for the fuse?


All the best
Ferdinand
 
DaSpark said:
Thank you Rob, will do.

Maybe a stupid question but how did you choose the correct dimensions for the fuse?


All the best
Ferdinand
Click to expand...
Do pigtail 2AG - or just don't worry about it. I've done plenty with no issues.
Replace every single fusistor there with 500mW or 1W metal film resistors.
3 on the power supply board, 2 on the protection board, and a whole mess of them on the driver board.

Do this before running the unit anymore!
 
Seeing that Sansui replaced these with fuses, that's what I did.

I remoted fuse holders.

Rob
 
DaSpark said:
Hello Everybody,

I just received a Sansui 990DB (my company was about to trash it) along with a Sansui SR-626.

The problem I have now is that there is absolutly no output whatsover. In addition the tuner also does not pick up any Signal (or at least the meter wont show it).

It will go out of the protection mode (light turns green).

I have tried supplying the power amps directly with a signal from my phone. Also nothing

I have read a few threads already. I checked (as fas as I could) the Tuner Power Supply. As far as I can tell there is no Voltage arriving there.

I have checked all five fuses on the the main power supply board. They seem to be fine.

I am a bit at a loss at the moment. Any help would be greatly appreciated. What would be the best way forward? What to check next?

How do you measure the voltages on the main power supply board? It is quite hard to access anything. (Plus i am a little afraid that i might touch the main caps and get a shock :D).

Attached are a few pics.

Thank you and all the best from Vienna.

FerdinandView attachment 1740885 View attachment 1740886 View attachment 1740887 View attachment 1740888 View attachment 1740889 View attachment 1740890 View attachment 1740891
Click to expand...
Are the main-in/Pre-Out jumpers installed on the rear?
 
DaSpark said:
Hello,

@Skywatcher: Yes the metal jumpers are installed. :)

@ivandezande and @Robisme: Okay will replace them with fuse holder like this: https://www.conrad.at/de/p/ptf-80a-...g-6-3-x-32-mm-6-3-a-250-v-ac-1-st-501262.html and get 5x20mm Fuses that fit: 1A slow should be fine right?



Thank you,
Ferdinand
Click to expand...
FAST blow only 1A. I used very short pigtail fuses. They are short glass fuses with leads on each end and solder in like the resistors.. Using those fuse holders you linked to will be awkward, but can be done. They would be my last choice though. Don't worry about the tuner working at this point. Build a DBT! A Dim Bulb Tester. Do some searching to find out what it is, and how to use it. It will save smoking anything. Get the amp to play first. Once the fuses are replaced we'll move forward.. Check to see if there is any DC voltage at the speaker terminals. Set the speaker switch to A, use A speaker terminals, and volume knob all the way down to zero. There should be something in the millivolt range. That will tell us if the amp section is getting power or not. Take it slow, you have a very nice unit and is well worth taking the time to do it right.
 
DaSpark said:
Hello,

@Skywatcher: Yes the metal jumpers are installed. :)

@ivandezande and @Robisme: Okay will replace them with fuse holder like this: https://www.conrad.at/de/p/ptf-80a-...g-6-3-x-32-mm-6-3-a-250-v-ac-1-st-501262.html and get 5x20mm Fuses that fit: 1A slow should be fine right?



Thank you,
Ferdinand
Click to expand...
Also, there are bleed resistors on the 2 big main filter capacitors. They will drain off the juice in about 10 minutes or so. But wait about 20 minutes to be safe. Then you won't get a new hairdo from them. :D Be aware that some smaller caps can hold a charge too, but they are small potatoes compared to the big ones.
 
Thank you all for the replies,

Did you also replace the fusable resistors with more than 1Ohm just with a fuse? There are fusable resistors on the driver board with 4.7, 10, 150 and 180 Ohm. Does this not matter? Or did you use a conventional resistor in addition?

All the best,
Ferdinand
 
I only replaced the two resistors in question with fuses, as Sansui did. Fuse only, to replace the resistor.

Too long ago to remember what else I did to it.

Rob
 
Rob, are you stating you simply put fuses in place of the resistors? Or put a metal film resistor of same value AND a fuse to replicate the function and value of the fusistors?

I ask because when I reworked my 9090DB years ago I just put metal film resistors of identical rating in lieu of the old fusistors, and have never had an issue. Now I'm wondering if I need fuses instead to have things properly protected.
 
DaSpark said:
Thank you all for the replies,

Did you also replace the fusable resistors with more than 1Ohm just with a fuse? There are fusable resistors on the driver board with 4.7, 10, 150 and 180 Ohm. Does this not matter? Or did you use a conventional resistor in addition?

All the best,
Ferdinand
Click to expand...
Use whatever the value is on all other fusible resistors and replace them with metal film resistor of the same rating. If one is a 4.7 Ohm, use a 4.7 Ohm, replace a 10 with a 10 and so on. Using 1/2 watt for all on the driver board. You don't want to use carbon film resistors because they can't take the heat that metal oxide, or metal film can. Carbon resistors will go up in smoke.
 
Sansuiman said:
Rob, are you stating you simply put fuses in place of the resistors? Or put a metal film resistor of same value AND a fuse to replicate the function and value of the fusistors?

I ask because when I reworked my 9090DB years ago I just put metal film resistors of identical rating in lieu of the old fusistors, and have never had an issue. Now I'm wondering if I need fuses instead to have things properly protected.
Click to expand...
Only for the two mentioned above on the power supply board on the violet wires. But if you used 1 Ohm metal film resistors there, and it's still working, you could leave them be. As long as you don't go tinkering around to short anything :yikes:, you should be fine. I personally put the fuses in there to protect the transformer "just in case".
 
Skywatcher, that is what I did, and had always assumed that any failure that would open the fusistors I repelaced with metal film would similarly destroy (via heat) the metal film resistors even though they weren't specifically made to act as fuses.

This was years ago, and it appears the thinking on replacing these may have evolved toward actually placing fast acting fuses in these circuit locations. Hence, my question.

If it is the opinion of the esteemed members of this board that just metal film resistors of original value are an adequate solution, I'll leave it be. If I'm risking further potential damage by not specifically having fuses installed at the locations formerly occupied by fusistors, I'd like to know.
 
Sansuiman said:
Skywatcher, that is what I did, and had always assumed that any failure that would open the fusistors I repelaced with metal film would similarly destroy (via heat) the metal film resistors even though they weren't specifically made to act as fuses.

This was years ago, and it appears the thinking on replacing these may have evolved toward actually placing fast acting fuses in these circuit locations. Hence, my question.

If it is the opinion of the esteemed members of this board that just metal film resistors of original value are an adequate solution, I'll leave it be. If I'm risking further potential damage by not specifically having fuses installed at the locations formerly occupied by fusistors, I'd like to know.
Click to expand...
It's been a while, but if I recollect correctly, they were only 1/4 watt resistors. If so, and you used 1/4 watt you could probably leave them be. If you used 1/2 watt, you might want to consider using fuses. The 9090db uses 1.5A fuses in that position.
 
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