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9090, looking to repair/recap

R

Rx7man

New Member
Hello.. I was given a 9090, and it was dead.. protection circuit fault, I found the troubleshooting guide and replaced a few caps, it worked for a minute or two and quit again.. this time blowing the right channel fuses..

So, despite that it's not in great condition, I hear it's still worth putting into good operational condition, and I've done a bit of this before on my Marantz 2275... I know not all parts are available and there will need to be some substitutions...

One thing I noticed is that a lot of the electrolytic caps are a much bigger form factor that 'current' manufacturers make for a given voltage and value... Would there be any harm (or benefit) in increasing the voltage rating (thus size) of a cap so that it fits like the original?.. IE, upping a 6.3V to a 16 volt? (My physics 101 class memory tells me this would be fine, but want to be sure)
Fuse resistors, well, I saw those can be changed with fireproof 1/4 watt of the same rating..

The varistor diodes haven't been broken (thankfully) (yet), but I'd like to change out all the signal transistors and protection circuit transistors while I'm at it, as well as the trimpots.. Might as well do it right, right?

I have found the manuals for the 8080DB and 9090, but my driver board is the F2436-1, and I'm not finding a schematic for that, just for the F2436... The case says it's just a 9090, not a 9090db

I'll work on a Mouser BOM and post it, you folk can tell me if there are some things I need to reconsider
Thanks!
 
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No harm in increasing 6.3V caps to 10V or 16V, and it shouldn't change the price too much.
 
I wouldn't up the cap voltage if modern caps had the same lead spacing, I'm just thinking of doing it to make them fit nicely. On the smaller ones it isn't going to break the bank
That is a great list! I haven't used Digikey yet,.. Last I checked they charged an arm and a leg for shipping. I'll just have to add some resistors and transistors to that.

I got my manual from eserviceinfo for the 9090, it shows the F2536 driver board, but not the F2536-1 board, and there seems to be a significant difference, especially when it comes to part numbering. The manual I have is certainly legible.
 
There would be a minor advantage to using a higher voltage cap if it fits. There are things that effect capacitor life, the biggest one is temperature. For every 10C under the rated temp you operate, you double cap life. The more you de-rate the voltage on a cap, the more life, though not near as big an impact as temperature. I as a rule like caps to be rated 150% of the working voltage when designing circuits using EC caps. I recapped my 9090DB using Toms list, nicely done :thumbsup:

Joel
 
You really want to diagnose the issue before wholesale replacing parts - not sure if that is your plan or not. Your fuses blowing most likely isn't being caused by caps - that would be the last suspect in my book. Setup the DC offset and bias for each channel as the very first thing that you do - using the procedures that you hopefully have in the manual.
 
@slimecity You're right that the problem probably isn't caps, but if I'm going to re-cap anyhow, why not right? I have a few of the fuse resistors that show serious signs of heat, of course they'll get done at the same time too, and I'll look at the smaller transistors as well.. for the price of them I probably might as well. I will be looking into the DC offset as well, though I don't see how you can adjust the DC offset when the fuses are blowing.
Is it possible (or wise) to bypass the protection circuit for testing purposes?
 
Its probably not possible to bypass that circuit - I wouldn't know. But if the amp is running stable it will stop blowing fuses etc. You don't want to bypass protection measures. Does the SM detail the calibration procedure? You could set all the pots to 0 and slowly wind them up. Depending on what fuses are blowing, its likely that the bias setting is currently too high and this is causing the fuses to blow. As a general guide, you don't want to introduce new things before you fix the existing problem. I have been there - many times, and had to retrace my steps and "undo" a lot of work that may have contributed to a problem. Just my two cents.
 
slimecity said:
You really want to diagnose the issue before wholesale replacing parts - not sure if that is your plan or not. Your fuses blowing most likely isn't being caused by caps - that would be the last suspect in my book. Setup the DC offset and bias for each channel as the very first thing that you do - using the procedures that you hopefully have in the manual.
Click to expand...

In this case, I disagree. Get stable, known good ECs in there before setting DC offset and bias, or he'll just be doing it all over again.
 
I agree with slimecity (sorry Sam), Rx7man, you really must stop the unit blowing fuses, by fixing whatever fault(s) it has, and demonstrate (not to us) that you can set DC offset and bias - when you can do those things successfully then and only then proceed with a recap.

You will always want to check and reset the DC offset and Bias anyway after a recap (you ARE going to change the trimmers aren't you?) - so it's no big deal doing it twice, or is it?
 
I've done the DC offeset on my Marantz 2275.. Just resetting DC offset is no big deal, doing it 10 times is alright by me... but I'll have to go back and re-read the 'common sansui problems' sticky on blowing fuses and protection circuit.. I think this thing may have had several problems when I got it, which makes it harder to diagnose... I know for sure there were several blown caps on the driver board, I replaced them already, but there may be more that are dead, just not bulged out (fixed a motherboard once that suffered of the same problems when the SATA port would die and I was getting random crashes). I did get a pile of trimpots in my last Mouser order, I might even have the right ones in stock...

One of the problems it had was one of the traces on the driver board was corroded out, I blue wired it back.
 
Rx7man - how was that trace corroded, by extreme atmospheric conditions, or leaking cap fluid? Why I say don't bother at this early stage with recapping is that 90% of the time caps display visual signs before they go kaput - either by bulging or leaking (as you have noted). The more urgent problem to me could be easily addressed by recalibrating. I'm going thru the same thing with an Accuphase P300 at the mo, calibrating and re-calibrating after I replace parts and try to find a fault in the protect circuit......
 
Took all the output transistors and driver board out, started up without blowing fuses.. put 1 pair of outputs in, all good, put the 3rd one in and pop, so I think that one is shorted..

Is it possible to derate the 9090 to an 8080 and use 1 pair of transistors per output? Will have to change the bias current to 8080 spec (30ma IIRC instead of 100ma)... At least until I source other transistors for it.. I'm not in a hurry for this thing to work, perhaps I'll stumble on something at some point.
 
Yea that's a hassle, and adds a new layer of complication I guess - have you gone over all the traces thoroughly with a magnifier to look for any other damage/corrosion/cracks?
 
Rx7man said:
Took all the output transistors and driver board out, started up without blowing fuses.. put 1 pair of outputs in, all good, put the 3rd one in and pop, so I think that one is shorted..

Is it possible to derate the 9090 to an 8080 and use 1 pair of transistors per output? Will have to change the bias current to 8080 spec (30ma IIRC instead of 100ma)... At least until I source other transistors for it.. I'm not in a hurry for this thing to work, perhaps I'll stumble on something at some point.
Click to expand...

I don't see why it wouldn't work. The 9090 transformer would be loafing along with the extra bank of transistors out of circuit.
 
Sam Cogley said:
I don't see why it wouldn't work. The 9090 transformer would be loafing along with the extra bank of transistors out of circuit.
Click to expand...
That's what I figured, and I can live with 75WPC.. Bigger heat sink relative to the load as well is good for the output transistors too... it's just a matter then of setting the driver board up right.

Then at some point I might find a new set of output transistors for that channel and bump it back up to full power.
 
OK, this is going to hell in a handbasket.. for no good reason (I didn't change anything, I was about to adjust DC offset, it was 60mv) the one working channel is messing up.. output transistors are heating up like heck, it blew the main fuse.. removed driver board, replace main fuse, and it behaves.. no go with driver board installed.
Protector circuit is still not engaging.. disconnected input leads and ground inputs to ensure DC offset it sees is 0V, nope.. going to check transistors now.

I'm seriously considering completely rebuilding the entire board, perhaps even with a topology change (perhaps MOSFET output stage).. I know it's not going to be a REAL 9090 after that, but this thing isn't in collectible condition anyhow. Might have some spare genuine 2SC1116's if that's what I go for.
 
While the fusistors did look like they got hot at some point, they were all right on spec when I removed them and tested them.. I will be replacing them anyhow
 
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