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

KeithD

KeithD

AK Subscriber
Subscriber
Just wondering what the prevailing thought on this is. Picked up a 9090 last week. Cleaned the inside. Volume/balance pots scratchy. Treated with Deoxit followed by Fader lube, and that completely cleared up. It has the modifications to the amp board, which likely were done at the factory since the unit has a February 1977 serial number. Everything looks stock inside. Fairly clean. Cleaned out dust/cobwebs in there and on both sides of the heat sinks, but no corrosion that I can see.

So, it seems to be working perfectly. Can't see or hear a flaw (tuner could use an alignment, though). My inclination is to just use it as-is. I'm not hearing any problems at all. But, what is the consensus? Do people do some minimum upgrades - change e-caps? What are the pros/cons of not changing anything?
 
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You won't know how great these can sound until you refresh the electrolytic caps. Also can improve with film caps in a few areas and some bypass caps on main filters.
I would at a minimum change out the VD1212 diodes and the fusible resistors.
I do have one that is stock that I use, but it is sometimes slow to come out of protection and is on the short list to go through.
Just finishing up a 8080 that sounds like a completely different unit now. Many steps up from where it was.
 
^Yep, what he said. Mine was completely original as well and worked flawlessly. I was a bit hesitant to go through it, but I did after some encouraging words from the great people on this site. Well worth the time and effort.
Nice piece of gear for sure.
 
I agree on, at minimum, replacing the vd1212s and fusible resistors on the driver board. Next would electrolytics in the power supply. The 9090 is relatively easy to work on....especially the driver and power boards.
 
Do the fusible resistors and the vd1212 diode replacements for now. They can cause sudden loss of stability in the driver stage and blow a channel (or both). Visually inspect all electrolytic caps in power supply and driver stage for any bulging or leakage out the bottom onto the board, any found in such condition need replacement. Everything else should be safe for now, even if not ideal. Key thing is to avoid sudden catastrophic failures that do real damage.
 
I found these from a post made in 2007. Are these diodes still the best replacement for the vd1212?

"SV-02Y or a pair of 1N4148's"
 
tnsilver said:
It biases right? DC offset near zero? so I'd like to go against the grain here. If it ain't broke... ;)
See? No consensus already. Good instincts. Use the force Luke.
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I agree with Tom, in that if everything looks good like Bias and DC balance, and the controls are now cleaned up, does it really make sense to mess with it?
While many of us are here more than willing to assist in resolving issues and giving guidance, unless you are trained on component level repair, and have many years experience, there is always the possibility of "I accidently touched something with my meter lead while measuring some voltages, then there was a spark/flash, and now the receiver won't come out of protection". Old techs like myself would say "oh well, let me see what I shorted, and fix it". Others not so experienced might have to say "OH ****"

The thing that you can do that makes the most noticable difference, was already done by your cleaning a deox of the switches and controls.
 
^^^ while I'll concur with Tom's remarks above about avoiding fat fingered mistakes causing damage, the fusible resistors and VD1212 diodes on the driver board are a widely known source of failure that blows output transistors when they go off value. And they will, at some point. Virtually every bone stock 9090 will have this failure if not addressed proactively (and they're closing in on 45 years old now, so component value drift is a real and present concern).

It can be avoided (the loss of output devices and other related damage) by replacing just the handful of resistors and diodes that are known to go badly off spec. Not replacing these is analogous to playing Russian roulette with the output stage on the 9090 and related models using similar driver boards. It will blow at some point, and then the repair is a lot more involved and expensive.

The driver board is pluggable, so easy enough to remove and do work on unless you know absolutely nothing at all about soldering and electronics work. Even then, unless one possesses no mechanical/technical aptitude whatsoever, this type of repair should be doable once some basic tools are acquired.

Running a 9090 with the old fusible resistors and VD1212's is kind of like driving a car with a bad oil pressure sensor. The oil light keeps coming on even though there's 6 quarts in. Then one day, the oil leaks out due to a loose drain plug and now you seized the engine because "the oil light is always on, it's just a bad sensor so I ignored it". Or as I'm fond of saying, it is what it is - until it isn't.

Even if you have to pay a tech to do the work, it will still be less costly than a full rebuild of the driver board and outputs should one or both channels get blown. A full recapping, while certainly in order, can be done later as budget permits.
 
After cleaning it up, I did set the DC offset to zero and the bias current to 50mV on each channel per service manual.

I've read the fusible resistors need to be replaced on Sansuis that used them, so that makes sense. What do they look like so I can tell if they have already been replaced? Here's a picture of the driver board:

F2436 side.JPG
F2436 front.JPG

What are the recommended replacements?

I do have a fair amount of experience soldering and working on Pioneer equipment over the past few years, so that is not a problem.

I tend to agree with the two Toms at this point and approach stereo equipment with caution. I spent a lot of time totally recapping a Pioneer SA-8100. Forum consensus was it would sound so much better with a total recap. Did it sound noticeably different? Yes. Was it a big difference? No. Was it better? Unsure. Everyone has different taste in sound, so it was different, but can't say it was really better (it was already good to my ears), and the effort for the benefit was definitely not worth it, other than what I learned.

At some point I started measuring capacitance of every e-cap I pulled out. Conclusion: most original e-caps <10µF rating were outside their spec of ±20%. Less than 10% of old e-caps >10µF rating were outside of their spec. Now, I have a small sample compared to most of you that have a lot of experience, but it did start me wondering if I should really be replacing all of those e-caps, just because...

So, I lean more toward preventing problems than looking for improvement in performance, which can be subjective.
 
KeithD said:
What do they look like so I can tell if they have already been replaced?
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See post #20 in the linked thread. ;)

The two larger (grey) resistors near the trimmers at the top of your pic are not fusibles - need checking but leave if OK.
 
KeithD said:
At some point I started measuring capacitance of every e-cap I pulled out. Conclusion: most original e-caps <10µF rating were outside their spec of ±20%. Less than 10% of old e-caps >10µF rating were outside of their spec. Now, I have a small sample compared to most of you that have a lot of experience, but it did start me wondering if I should really be replacing all of those e-caps, just because...
Click to expand...
Caps are an interesting component, capacitance is one thing, ESR is another but those small hand held capacitance meters don't really tell you much about the real health of a cap.
It might have 10µf and be on spec for a 10µf cap, but its not telling you how quickly of charges up and just how leaky it really is.
They will tell you that a VERY leaky cap is indeed leaky, but with the proper data you can forecast the health and life expectancy of a cap...
Many people do not have this ability and the gear to do it, nor the time, so the best cause of action is to replace the caps, the cost is fairly minimal and whilst it may take some time, its well worth doing.
All the caps in your 40+ year old 9090DB are well past their service life, and the best cause of action for reliability is to go through and replace them.
 
Really it seems like you pretty much know what your doing. So it seems like if you "chose to just "recap" the thing and call it day ...you'd be fine. :)

But if you do ... you'd "skip over the whole" was this worth the effort bit??? I think it's safe to safe to say that it would benefit from recapping! I'm sure there is no debate on that?? But hey it seems you got a good unit! So you have "options" I'd suggest ... fix the weak points as suggested, and leave the rest of it alone. Enjoy it as it is for a few months and then if you "choose" go back in and recap the beast.

If you "recap" it out the gate ... you'd lose your "before and after" window?? I tend to think that a big part of the whole vintage thing is first find great vintage gear at a price!! And second listening to it and seeing if I can make it better??? If you recapp the the whole unit "out the gate??" You'll have a better unit "no doubt" but you'll have lost a degree of "Satisfaction in a job well done" I think??


just a thought. :)
 
Is there an up to date BOM for teh 9090? I pulled one from AK last week, but it is not complete and some parts are not available.
 
Yes, that is the one I had downloaded from your 2012 thread. You don't list any replacements for the fusible resistors on the driver board, so was wondering what is recommended there? Also, the listing for C07 and 08 (Nichicon UESOJ101MPM) does not turn up anything at Mouser.
 
KeithD said:
Yes, that is the one I had downloaded from your 2012 thread. You don't list any replacements for the fusible resistors on the driver board, so was wondering what is recommended there? Also, the listing for C07 and 08 (Nichicon UESOJ101MPM) does not turn up anything at Mouser.
Click to expand...
here's the mouser number for that cap.
647-UES0J101MPM
 
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