How to start a recapping?

[Rattakat]

My Sansui AU-3900 is working. But after years of usage it sometimes plops. When i opened it i see why. One of the filtercaps is gone.

I want to restore this thing because it was for years my best friend at my computer table. After getting smarter how to look up schematics i found out you need more. What now?

 

[cyrano]

The first thing I do, is make a list of all the electrolytics. I print that list and start desoldering and measuring. Even if I replace all of them, it's interesting to see how many of the caps are bad.

Once the caps are replaced, I start measuring voltages and comparing them against the schematic. If a schematic is available, of course. Any measurements that are way off, usually allow me to find bad resistors or bad transistors, bad switches...

Than you still need to clean pots, switches etc.

The Sansui AU-3900 is certainly worth restoring.

 

[Script]

Schematics or not, I first put a mark (permanent marker) on top of ALL old caps plus take several pictures -- then replace one cap at a time or several at a time but only if those caps are of one value (eg. 22uf). This way there's no confusion (same or following day or week later) of what goes where and what has and what hasn't yet been replaced.

With some (old) boards, cap orientation can be a bit unclear after desoldering, so I mark the PCB.

 

[living sounds]

It's always a good idea to shoot a lot of pictures from various angles before attempting any changes to gear.

 

[Tubetec]

Id consider just changing what very obviously needs changing first ,then see if the issue is gone , definately replace the main filter caps
There may be no great need to do anything beyond that unless theres an issue ,
Looks like all radial mounted caps which means getting modern replacements is easy in any case .
A random spot check of electrolytic coupling cap values will tell its own story .

 

[TwentyTrees]

Lots and lots of reference photos! I also measure dimensions of all the caps before I desolder them - height, diameter and pitch - to make sure my replacements will fit nicely.

 

[user 37518]

Some people like to take out all the old caps and then put in the new. That might be faster, but I prefer doing one at a time to make sure I get everything right.

 

[pucho812]

Whenever a recap is in order before doing any of the actual work, you got to do a lot of legwork. Ideally, you can get schematics, but if you can’t, you should be able to recap regardless. So what I always do first is make a list and double check it of every capacitor value. I will next test caps with my Tester. Then I will mark all the capacitors needing to be changed with a sharpie. I do the mark so that it’s visible, but still allows me to see the value of the capacitor. Lastly, I ordered what I need.
The more prep work , if you can do ahead of time, it will be easier when you actually have to do the work

 

[Ike Zimbel]

Schematics or not, I first put a mark (permanent marker) on top of ALL old caps plus take several pictures -- then replace one cap at a time or several at a time but only if those caps are of one value (eg. 22uf). This way there's no confusion (same or following day or week later) of what goes where and what has and what hasn't yet been replaced.

With some (old) boards, cap orientation can be a bit unclear after desoldering, so I mark the PCB.

I have run across at least two devices over the years that had mistakes on the cap markings printed on the board, so pictures AND marking the polarity is a very good idea. It's been a while but I believe one of the devices is the early API-550 Eq module has a decoupling cap marked backwards on the board, and the other device is a fairly recent 24v SMPS that gets used in a line of gear that I service and sell.

 

[Ivan K.]

In addition to the above advice, I'd recommend 105 deg C, long life (5000hrs min), low ESR caps. Since larger, modern caps are usually 10 to 20% lower in value than marked to save money, I'd increase all the PS caps by the next higher value, or more. Also, check new cap lead spacing, diameter and height.

Unless you have a good cap tester with Kelvin clips, ESR is tough to measure accurately. I recommend a UK company, Peak Atlas ESR Gold ESR Plus model ESR70 | Peak Electronic Design Limited. $94 at Digikey in the US

 

[Script]

Careful with caps glued onto PCB.

I tend to cut off as much glue with an exactor knife as possible -- without damaging the board !!

Then preheat the cap with a HOTGUN (if at hand) until glue starts to melt.

And/or use bigger iron (higher temperature) for desoldering, hoping that the cap absorbs enough heat to make the glue gooey again. Meanwhile carefully wiggling the cap. This might take a while.

Either way it's important to not use too much force, as that might rip a trace/via of the board. Cos then you'd have to restore it with a wire and mask it with UV curing solder mask ink (see pic) or nail polish.

 

[58Glammer]

Id consider just changing what very obviously needs changing first ,then see if the issue is gone , definately replace the main filter caps
There may be no great need to do anything beyond that unless theres an issue ,
Looks like all radial mounted caps which means getting modern replacements is easy in any case .
A random spot check of electrolytic coupling cap values will tell its own story .
View attachment 103203

I never go half way if an old unit‘s elcos start to be bad and leak. I change all electrolytics then. It makes no sense to just exchange the bad ones as the others will start to be bad soon after. Then you need to start over again with opening the unit, looking for the failed elco ect..
I start with the PSU and continue with the rest. Get good brands like Panasonic or Nichicon I saw some good tips like using a marker for the old ones Superimportant.. and if there‘s no +/- markings on the board (e.g. Roland SVC 350 Vocoder) make them markings yourself..

 

[Tubetec]

The Japanese makers did tend to use very strong glue to secure psu caps down , it doesnt allow much movement when the component internals heats or cools , you sometimes see hot glue around the edge or silicone sealant to anchor the cap body to the pcb .

If your starting out 'new to electronics , try not to jump in out of your depth is my advice ,
Just do what needs to be done , ok the Sansui is probably close on 40 years old but that doesnt mean all the eletrolytics have failed or are about to ,
Sure measured values maybe somewhat low across the board and ESR will have crept up but if the designers did their job right it will have minimal impact on the sound . A piece of equipment that has lived its whole life in the relatively stable conditions indoors can last 70 years and still work without a major surgery Something thats lived 20 years in the chicken shack, unheated garage or shed isnt likely to work well at all .

If your amp is back to working the way it used to after replacing a few main caps , leave it at that , return to enjoying the tunes and find the next project .

Learning to use the soldering iron at the correct temp and of the right wattage for the job is key , minimal dwell time on work area is also hard to master at first ,take a few scrap PCB's and try out using the solder vaccuum pump and solder wick to remove a few components and clean up the traces , then resolder the old part back in ,
PSU caps tend to have heavy traces and require much more heat than the other smaller components to solder , to much heat for too long , you lift a trace and you've needlessly made work for your self .

 

[Mr. Moscode]

My advice is to get the schematic and where you find capacitors in the audio path replace them with 50 volt film caps. They have 5 mm lead spacing and should fit in quite a few places. They are non polarized so you can't put them in backwards, either. The amp will sound cleaner.

If you can get the schematic post it here and we can help you sort it out.
Happy Soldering

 

[Mr. Moscode]

You may be able to put in power supply caps of the same voltage rating but larger in value, like instead of 10,000 mfd, maybe 22,000. The cap technology has gotten a lot better in the last 40 years with higher capacity in smaller packages.. Also Nichicon makes caps for audio use, supposedly with better characteristics for audio. That will give you more reserves for bass whomps and cleaner high end.

 

[JohnRoberts]

I am not a big fan of end users second guessing design engineers (guess why?). My standard advice about recapping is to measure first, to benchmark performance to help identify outliers (generally low capacitance due to loss of electrolyte over time). If you find an obviously bad capacitor replace all of the same type/value as they are also likely to be on the way out.

Modern caps are generally smaller and better, both good things.

JR

 

[Ike Zimbel]

Careful with caps glued onto PCB.

I tend to cut off as much glue with an exactor knife as possible -- without damaging the board !!

Then preheat the cap with a HOTGUN (if at hand) until glue starts to melt.

And/or use bigger iron (higher temperature) for desoldering, hoping that the cap absorbs enough heat to make the glue gooey again. Meanwhile carefully wiggling the cap. This might take a while.

Either way it's important to not use too much force, as that might rip a trace/via of the board. Cos then you'd have to restore it with a wire and mask it with UV curing solder mask ink (see pic) or nail polish.

Good point. This is especially true for phenolic circuit boards, which a lot of HiFi gear uses.

 

[Whoops]

If an electrolytic can has already failed other are already not up to the task or will start to fail soon. Also the unit is old so the Lytic capacitors are already past it’s lifetime.
Replace All Electrolytic caps in the unit, easy and cheap. Don’t replace just the ones with the value of the one that failed and don’t replace only that one, replace ALL

There’s already great advice in this thread.
I recommend Panasonic branded capacitors, any series of Panasonic, rated at 105 degrees

 

[living sounds]

In addition to the above advice, I'd recommend 105 deg C, long life (5000hrs min), low ESR caps. Since larger, modern caps are usually 10 to 20% lower in value than marked to save money, I'd increase all the PS caps by the next higher value, or more. Also, check new cap lead spacing, diameter and height.

Unless you have a good cap tester with Kelvin clips, ESR is tough to measure accurately. I recommend a UK company, Peak Atlas ESR Gold ESR Plus model ESR70 | Peak Electronic Design Limited. $94 at Digikey in the US

I would recommmend not to use low ESR caps where standard caps were used. They can actually be detrimental and cause problems. Mainly stability, in cases where the circuit actually relies on the cap resistance for stability.

In the signal path I also often had the impression that many low ESR caps were not well suited for the reverse polarization (however brief) caused by AC (audio) signals.

I like to replace signal path caps with bigger and / or bipolar caps where it makes sense. Measurements show that bipolar caps offer far better low end distortion specs than polarized caps.

As for brands, I like Nichicon, especially the audio line, and the red Würth caps.

 

[Whoops]

I would recommmend not to use low ESR caps where standard caps were used.

All modern caps are low ESR though.
I never, ever had any problem with recapping with a lower ESR capacitor, neither I know anyone that did.

If the Op re-caps the device with any Panasonic or Nichicon cap he will be fine, no need to make it complicated, it's a simple operation

My 2 cents