Sansui 9090: Original, everything works. Should I change anything?

When I recap one of my units it is generally for the purpose of preventative maintenance. Any improvement in sound quality is a bonus.
 
If you decide to realign the tuner, have a qualified tech do it. That isn’t a job for first timers.
 
If you decide to realign the tuner, have a qualified tech do it. That isn’t a job for first timers.
Totally agree. Even if I had the equipment I would practice on a low-value, low-risk tuner. I've e-mailed a couple of places in the Minneapolis area that do repair and have had no response. It may be tough for me to find a qualified person/place to do it.
 
C07/C08 are just 100uF/6.3V bi-polar caps like all of these. You got to pay attention to the lead spacing. I didn't do resitors back when I made the recap list, but I like to use KOA Speer metal-oxide 1% or 5% tolerance resistors for the fusibles. For example, for R29/R30 (390Ω) I'd go with this and for R43/R44 (22Ω) with this. The list tells you which are the fusible resistors - so you can look it up by using Mouser's MOX resistors filters.
Thanks for those clarifications, Tom.

here's the mouser number for that cap.
647-UES0J101MPM
Thanks for that, Kev.

When I set the DC offset, the VRs were pretty touchy. So, it might be good to replace those. What have others used for the driver board trimmers? I've not replaced trimmers before, but this may be a good place to do it.
 
I know that Classicaudio.com in California is well versed in tuner alignments.
Thanks, but I'm looking to find somewhere in driving distance, so that is in the Minneapolis, MN to Milwaukee, WI region.

If I were going to ship it out, I would send it to QRXRestore. However, a complete restore on a 9090 (which includes an alignment) is $575, so that's a big commitment.
 
When I set the DC offset, the VRs were pretty touchy. So, it might be good to replace those. What have others used for the driver board trimmers? I've not replaced trimmers before, but this may be a good place to do it.
Just get some bournes multi-turn trimmers...
Go here and then select how many turns, mW, and value.....easy.....
Some amps I use the top slot 500mW 4 turn, but most times 250mW is what you want.
 
As I read more about the fuse resistors, a question arises. When the fuse resistors on the driver board are replaced with metal film resistors, I can see how they replace the resistor function of the original fuse resistors, but what happens to the fuse function? Are there other safeguards in place on the board that the fuse function of the fuse resistors is not needed?
 
As I read more about the fuse resistors, a question arises. When the fuse resistors on the driver board are replaced with metal film resistors, I can see how they replace the resistor function of the original fuse resistors, but what happens to the fuse function? Are there other safeguards in place on the board that the fuse function of the fuse resistors is not needed?
Metal film just burn up which is why you mount them standing off the board. The only situation a fusible resistor will let go is because a semiconductor has failed, so as long at the metal film is of the same wattage as the fusible resistor, you are good to go, its not an issue it will do its job and save the rest of the circuit.
 
Metal film just burn up which is why you mount them standing off the board. The only situation a fusible resistor will let go is because a semiconductor has failed, so as long at the metal film is of the same wattage as the fusible resistor, you are good to go, its not an issue it will do its job and save the rest of the circuit.
OK, thanks Kev, that makes sense. So is it the case that when a fusible resistor acts like a fuse it creates an open circuit - like a fuse would? It seems like no one replaces these with a fuse+resistor in series - probably impractical, or maybe overkill?
 
Yes , you could replace a fusible with a conventional fuse and a time delay (slow blow) fuse, or use a modern fusible resistor (yup, they are still around). On the other hand a good metal film resistor will also act the same way under high current transients (self destruct). Remember that most of the fusibles in Sansui gear are very low wattage so we are not talking significant amps here. Just install the replacements 1/4' or so above the board to protect the board if one does let go.
Back on topic again, at a minimum change out the trimmers and the fusibles taking note that the traces on the original 9090 driver boards are very very frail and will not tolerate heavy handed component removal. Also study the trimmer adjustment procedures as they are different left to right. Finally be ultra careful when putting that board back in, it is easy to get it one pin off and really hurt things upstream.
-Lee
 
Protip: On your power supply board there are 4 fuses right under the driver board. Check and see if those are 10amps- if they are change em out for 6A or 7A. If you choose to not restore the amp, that just may save you a lot of headache further down the line. Those 10A don't blow with a shorted output TR. That said, It'll sound SO much better if you recap it, and be much more reliable if you replace the fusables.


p.s. 9090 you can't get the pins messed up on. just the 9090db

p.p.s. Thanks from QRXrestore for the shout out!
 
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Not sure what I am going to do with the receiver at this point. It really sounds good and works flawlessly. I understand that the fuse resistors go out of spec and become unreliable over time, but if I understand it right the worse that happens is one fails causing an open circuit and likely putting the receiver into protection?

I'm not clear what the VD1212 problem is. I do have the replacements on hand, but what problem does a failure of one of these cause and why are they prone to failure?

Replacing e-caps is a whole other issue. I understand that they can go out of spec over a long period of time. In my experience (which is limited) e-caps below 10 µF are more likely to be out of spec than larger caps. If an e-cap tests out of spec, it should be replaced. However, I have changed my mind on wholesale re-caps. So many of the caps I have pulled out tested in spec, making me question why I was pulling them out in the first place? I was doing it because the majority opinion is they should be replaced. There is no harm in replacing all e-caps (unless you make a mistake or cause another problem). However, is there really a need? I think this is subjective. My experience completely recapping a Pioneer SA-8100 showed very little change in sound quality after the recap. I learned a lot, but will not do that again.

So, unless I am at risk of potential damage to the 9090 by not replacing anything right away, I am taking a cautious approach. The main issue is I really want to know why I am doing something. Not just doing something because someone says it should be done. I have learned a lot from the great people on AK and I want to keep on learning and be smarter about stereo repair. I have done enough of following advice blindly on my Pioneer gear. Don't want to keep doing that.

Protip: On your power supply board there are 4 fuses right under the driver board. Check and see if those are 10amps- if they are change em out for 6A or 7A. If you choose to not restore the amp, that just may save you a lot of headache further down the line. Those 10A don't blow with a shorted output TR. That said, It'll sound SO much better if you recap it, and be much more reliable if you replace the fusables.


p.s. 9090 you can't get the pins messed up on. just the 9090db

p.p.s. Thanks from QRXrestore for the shout out!

Thanks for the tip on the fuses. Agree on the driver board for the 9090, which does not have the "pins" that the later models did. The "pins" are printed on the PCB and insert into a slot, so no way to mess that up.
 
Not sure what I am going to do with the receiver at this point. It really sounds good and works flawlessly. I understand that the fuse resistors go out of spec and become unreliable over time, but if I understand it right the worse that happens is one fails causing an open circuit and likely putting the receiver into protection?

I'm not clear what the VD1212 problem is. I do have the replacements on hand, but what problem does a failure of one of these cause and why are they prone to failure?

Replacing e-caps is a whole other issue. I understand that they can go out of spec over a long period of time. In my experience (which is limited) e-caps below 10 µF are more likely to be out of spec than larger caps. If an e-cap tests out of spec, it should be replaced. However, I have changed my mind on wholesale re-caps. So many of the caps I have pulled out tested in spec, making me question why I was pulling them out in the first place? I was doing it because the majority opinion is they should be replaced. There is no harm in replacing all e-caps (unless you make a mistake or cause another problem). However, is there really a need? I think this is subjective. My experience completely recapping a Pioneer SA-8100 showed very little change in sound quality after the recap. I learned a lot, but will not do that again.

So, unless I am at risk of potential damage to the 9090 by not replacing anything right away, I am taking a cautious approach. The main issue is I really want to know why I am doing something. Not just doing something because someone says it should be done. I have learned a lot from the great people on AK and I want to keep on learning and be smarter about stereo repair. I have done enough of following advice blindly on my Pioneer gear. Don't want to keep doing that.



Thanks for the tip on the fuses. Agree on the driver board for the 9090, which does not have the "pins" that the later models did. The "pins" are printed on the PCB and insert into a slot, so no way to mess that up.


Board is mirrored too, you can even put it in backwards if you want and it will still work. Pretty handy for trouble shooting sometimes. Truth is that you probably won't get a ton of time out of this amp without doing all the caps and fusibles, but as long as you replace those fuses you won't be replacing EVERY transistor on a channel when it does go.
 
Not sure what I am going to do with the receiver at this point. It really sounds good and works flawlessly. I understand that the fuse resistors go out of spec and become unreliable over time, but if I understand it right the worse that happens is one fails causing an open circuit and likely putting the receiver into protection?

I'm not clear what the VD1212 problem is. I do have the replacements on hand, but what problem does a failure of one of these cause and why are they prone to failure?

Replacing e-caps is a whole other issue. I understand that they can go out of spec over a long period of time. In my experience (which is limited) e-caps below 10 µF are more likely to be out of spec than larger caps. If an e-cap tests out of spec, it should be replaced. However, I have changed my mind on wholesale re-caps. So many of the caps I have pulled out tested in spec, making me question why I was pulling them out in the first place? I was doing it because the majority opinion is they should be replaced. There is no harm in replacing all e-caps (unless you make a mistake or cause another problem). However, is there really a need? I think this is subjective. My experience completely recapping a Pioneer SA-8100 showed very little change in sound quality after the recap. I learned a lot, but will not do that again.

So, unless I am at risk of potential damage to the 9090 by not replacing anything right away, I am taking a cautious approach. The main issue is I really want to know why I am doing something. Not just doing something because someone says it should be done. I have learned a lot from the great people on AK and I want to keep on learning and be smarter about stereo repair. I have done enough of following advice blindly on my Pioneer gear. Don't want to keep doing that.



Thanks for the tip on the fuses. Agree on the driver board for the 9090, which does not have the "pins" that the later models did. The "pins" are printed on the PCB and insert into a slot, so no way to mess that up.

VD1212 become unstable and unreliable with age and can, and will fail to cause problems in other areas.

Yes E caps go out of spec over a period of time, this is to expected and normal. They have a service life, when that service life has expired, generally about 20 years, then they can no longer be guaranteed to be reliable, depending on many different situations they may last a lot longer but I would not count on that.

There is a need to replace them, your basic meter cannot predict the life of a cap, and whilst it may test okay now, maybe next year, or maybe sooner, you might have some serious problems.
Experience tells me that from the Mid 70's, these caps are getting very close to the end of their life, as units I am working on from the early 70's late 60's are definitely done and should be all changed out.
Example, I am on my second of two AU777's and in both instances all the caps were reading more than a 100% over their rated capacitance, they are also showing a lot of ESR, there were some which the legs were corroded through....now these caps are only about 5 or so years older than the caps in your 9090DB there.

As far as sound quality changing after a recap, it really depends on the design of the amplifier and what caps you use to do the recap with. Some amplifiers show little change, the G series Sansui's show little change as they are mostly direct coupled with little or no Ecaps in the signal path. Something like a AU777 shows a huge difference.....

You are talking a risk not recapping something as old as a 9090DB, they are over 40 years old, twice the service life of the caps, you are on borrowed time.

And lastly, yes well I have just told you why it should be done, but you can do as you wish.....
I have just finished doing two G6700's which both had caps that had Ecap legs eaten by glue, and several Ecaps which were low value/leaky....Now these units were both from 1980....
So go figure....

A 1976 Pioneer SX1250 I did recently had the main 22,000µf caps ALL bulging around the vent, this is the same year as your 9090DB.

The amp is a time bomb, if you're in there, you might as well spend a few dollars on caps and get 'em done.......

But its up to you.....Personally I would be doing it.

Change the VD1212 and the fusible resistors, do not be foolish and think because they are fine now that they will be fine for any great length of time.
 
When replacing fusible resistors should the 1/4 watt fusible resistors be replaced with 1/4 watt or bumped up to 1/2 watt? I think I have read before that they should be replaced by 1/2 watt but that seems like it would be making it harder for them to fail and possibly causing more damage. I'm also asking this in regard to the 1/4 watt resistors in the 9090db driver board.
 
When replacing fusible resistors should the 1/4 watt fusible resistors be replaced with 1/4 watt or bumped up to 1/2 watt? I think I have read before that they should be replaced by 1/2 watt but that seems like it would be making it harder for them to fail and possibly causing more damage. I'm also asking this in regard to the 1/4 watt resistors in the 9090db driver board.
Replace with same wattage.
 
1/2 watt can tolerate more heat then 1/4 watt. Using a higher wattage couldn't hurt and it might help.

My 2 cents
 
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