Sansui 9090db headache

[Shole]

Hi everyone ,
I'm working on Sansui 9090db for a year now ,it's stuck in protection mod , i completely repaired 2624 board all output transistors, resistors capacitors , without 2624 board receiver goes off protection mod and signal from preamp is normal OK.
I use dummy load with light bulb ( 3x40w)
I know it's long shot but if somebody has working 2624 board that I can borrow so I can test the receiver it would bi amazing .
Thanks Nick

 

[tourmax]

Have you checked the bias and offsets?

You have to check the speaker voltages at the wires underneath if it's not coming out of protection, not at the speaker terminals.

My 8080DB did a similar thing after a rebuild, wouldn't come out of protection.

Once I set the bias and then the offsets at the board wires, it came out of protection and then worked as the service manual describes (IE: check offsets at speaker terminals).

I can't remember the exact wires that carry the signal and which board it was off the top of my head. I seem to recall it being a blue and gray wire, but don't quote me on that.

I think it was user "LBPete" that first pointed me to those wires......

 

[Scott Muni]

Plus 1 for checking DC going into the protection circuit.

That's an interesting heat sink for the tuner power supply.

 

[tourmax]

Plus 1 for checking DC going into the protection circuit.

That's an interesting heat sink for the tuner power supply.

That's a resistor for the tuner power supply I believe. There a thread on substituting them for the big ceramic ones on the Sansui receivers here on AK somewhere. Was mainly about getting the heat they generate away from the rest of the board components IIRC.

I bought a fistful of them back when that thread was still going on, but I never got around to trying it. They''re sitting in one of the parts drawers somewhere...

 

[eiraved]

Which transistors have you replaced? Only the ones on the F-2624 board?

 

[Scott Muni]

That's a resistor for the tuner power supply I believe. There a thread on substituting them for the big ceramic ones on the Sansui receivers here on AK somewhere. Was mainly about getting the heat they generate away from the rest of the board components IIRC.

I bought a fistful of them back when that thread was still going on, but I never got around to trying it. They''re sitting in one of the parts drawers somewhere...No

I was referring to the heat sink TR01 is mounted on, not the resistor mounted on the chassis. I have a slightly better location for the resistor if your interested.

 

[tourmax]

I was referring to the heat sink TR01 is mounted on, not the resistor mounted on the chassis. I have a slightly better location for the resistor if your interested.

Ah, I see now. I missed that first time through.

Sure, if you want to post it up I'll have a looky see. Always interested in ways to try and make these old rigs last longer...

 

[Scott Muni]

Ah, I see now. I missed that first time through.

Sure, if you want to post it up I'll have a looky see. Always interested in ways to try and make these old rigs last longer...

here..

9090DB tuner power supply thermal management... yet another thread...

The heat that comes out of the tuner power supply drives me nuts. I have removed the 2 ceramic resistors from the board and mounted a 200r on the tuner chassis inside the tuner box area. Still gets crazy warm, and there is no airflow inside the tuner box when the cover is in place. I have now...

audiokarma.org

 

[tourmax]

here..

9090DB tuner power supply thermal management... yet another thread...

The heat that comes out of the tuner power supply drives me nuts. I have removed the 2 ceramic resistors from the board and mounted a 200r on the tuner chassis inside the tuner box area. Still gets crazy warm, and there is no airflow inside the tuner box when the cover is in place. I have now...

audiokarma.org

Neat. Very clean looking unit inside. Looks like it's had some good care put into it.



My 8080DB has lead a far more "neglected" life, but I'm bringing it around. Now that it sounds great, I'm starting to work on making it "look" pretty....

 

[Shole]

Plus 1 for checking DC going into the protection circuit.

That's an interesting heat sink for the tune

Which transistors have you replaced? Only the ones on the F-26

I was referring to the heat sink TR01 is mounted on, not the resistor mounted on the chassis. I have a slightly better location for the resistor if your interested.

TI replace transistor TR01 2sd313 with bd 347 on big heat sink and now there is almost no heat.

 

[Skywatcher]

Hi everyone ,
I'm working on Sansui 9090db for a year now ,it's stuck in protection mod , i completely repaired 2624 board all output transistors, resistors capacitors , without 2624 board receiver goes off protection mod and signal from preamp is normal OK.
I use dummy load with light bulb ( 3x40w)
I know it's long shot but if somebody has working 2624 board that I can borrow so I can test the receiver it would bi amazing .
Thanks Nick

Check the DC Offset before the relay and adjust it to spec.. The Blue and Gray wires coming off the bottom of the main board are the speaker output that go to the relay board.
Clip to the one wire with the (+) lead, and ground the (-) lead to the chassis. Then do the other wire.

 

[Shole]

Check the DC Offset before the relay and adjust it to spec.. The Blue and Gray wires coming off the bottom of the main board are the speaker output that go to the relay board.
Clip to the one wire with the (+) lead, and ground the (-) lead to the chassis. Then do the other wire.

I just tried, voltage jumps fr-30v to +30v on both channels and I did check vr01 and vr02 they are good (4.7k)I can see my dummy bulb goes on and off .
without dummy load its 60v

 

[tourmax]

Yep, something is off there. The vr’s on my 8080db are super sensitive, but don’t swing like that.

Are these originals or replacements?

The originals on mine had a tendency to have large swings when touched. The new replacements were sensitive, but didn’t swing like the originals when touched.

Either way, I’d be leaning towards replacing them as they’re not expensive and quick and easy to change.

 

[Skywatcher]

I just tried, voltage jumps fr-30v to +30v on both channels and I did check vr01 and vr02 they are good (4.7k)I can see my dummy bulb goes on and off .
without dummy load its 60v

Definitely a problem. How did you "check" the trimmers? You need to recheck all your work step by step and find out what you missed, or did wrong. The main power board, driver board, and output chain of components including what output transistors and where you installed them on the heat sink. Your original post is quite vague. Clear photos of the F-2624 of both front and back will help. You may even have a solder bridge somewhere. And a clear photo with outer heat sink removed to see the transistors. Plus you do not use a dummy load to start with. That is only needed for final evaluation on an O'scope and for calibrating the power meters before hooking up speakers.

BTW, that looks like a nice clean unit. The "custom" heat sink on the RF power supply board TO-220 transistor is unnecessary but looks nice. I see you mounted a resistor on the tuner tray to absolve the heat issue of the original two 270 Ohm 5W ceramics in parallel on the board. I used a 135 Ohm 25W just like yours. I have also used pairs of 270 remotely mounted too.

 

[eiraved]

Have you checked TR701-708 for shorts, opens? You need to clearly spell out everything you have done to the 9090db for us to be able to help you.

As Skywatcher indicated, recheck all your work step by step and find out what you missed, or did wrong. No dummy loads are needed for the tests you are currently accomplishing. Is your volume set on zero while testing? Seeing as you're using dummy loads I'm guessing your volume isn't turned down.

 

[DougBrewster]

I just tried, voltage jumps fr-30v to +30v on both channels and I did check vr01 and vr02 they are good (4.7k)I can see my dummy bulb goes on and off .
without dummy load its 60v

That swinging arises when the channel is being over biassed and as the current rises in the output stage the current clamp (TR15/17 and TR16/18) pulls the output stage down until the clamp lifts and the cycle starts over. The fact that both channels are doing it suggests an incorrect component in each channel bias network or the bias pot is simply set way high.

 

[Skywatcher]

@Shole I use a TIP41C to replace the D313 on the RF power supply. And the same for other PS Pass transistors as well. They can handle both the wattage and heat without breaking a sweat. The heat isn't really an issue with it, as much as the two original pair of resistors that desolder themselves and cook the board. The traces on the board from them transfers the heat as well darkening the board. There is enough ventilation once you remotely mount those resistors to the tuner tray. That heat spreads out and isn't so concentrated to cause any issues. The cover does not seal against the tuner tray and some air does flow. There is also a gap in the RF power supply board for air to flow up through from below. You could even drill a couple of holes for more air flow on that end if it worries you. But I don't bother since these have lasted this long without remote mounting the resistors anyways, and will surely last much longer now. And by the time 50+ years comes, it'll need restored again anyways. The other end of the tuner tray is also wide open for air to flow. Other heat comes from the filament bulbs of the dial lighting, but switching to LEDs really reduces that heat.

 

[Skywatcher]

That swinging arises when the channel is being over biassed and as the current rises in the output stage the current clamp (TR15/17 and TR16/18) pulls the output stage down until the clamp lifts and the cycle starts over. The fact that both channels are doing it suggests an incorrect component in each channel bias network or the bias pot is simply set way high.

THIS ^^^ You need to set the BIAS pots to minimum resistance to start, then bring them up to around 20ma on the DBT to "test" with and be sure things are working. Then back them down to around 10ma or less before going on full mains power. Plus do NOT "trust" the original BIAS trimmers. They can go bad at any moment and swing full open. They have a limited cycle life, and you have no clue how many times they have been cycled (adjusted) through the years. Look at the Bourns datasheet and it will specify their cycle life.

 

[Shole]

My receiver is different than most I have seen. It's made in September 1977. When I bought it it was not working.
So, not clue what happened! When I opened it everything looked original .
When I unplug F-2624 board everything works , common sense it should be problem with F-2624 board
I attached photos of F-2656 and protection board and they are different then most that we can see on internet .
I don't have R-31 and r32 just fuse and look at the protection board , I just want to make it working so that is my reason to post in here if someone have same receiver and live near by( Vancouver,BC area)and willing to help

 

[DougBrewster]

Did you try to check bias?