Any Good Guides on Amplifier Re-Cap/Rehab?

Apologies if this has been covered, but the search didn't yield anything (though my search-fu may be weak).

I've been making some baby steps towards repairing my Sony STR-6800 SD. So far, that's involved replacing components on a power protection section of the board on which it looked like some resistors had gone out of spec and started to cook. Fortunately, nothing outside of that section of the board was damaged and things appear to be working more or less correctly with new components in place.

Likewise, I've cleaned the pots, though could probably stand to do a more thorough job and apply some Deoxit Gold to keep everything good and lubricated.

Which brings me to the ultimate question: has anyone here got any pointers or know of any decent guides for the steps that I should probably take to fully rehabilitate this receiver? At this point, it's kind of a pet project to get this thing back up to 100% functionality, so I don't want to outsource this to a tech (nor do I particularly want to spend the money).

Based on my reading, it sounds like I want to replace all or at least most of the capacitors in the circuit and potentially also all resistors in any of the power portions of the circuit. This is all fine except when we get to the monster caps coming right off of the transformer. I'm not super concerned about making the replacement - finding something of appropriate value and soldering it into place should be easy enough - it's more about making sure essential components are mounted correctly.

The way things are set up now, the large capacitor coming off of the transformer has some sort of metal ring or mount around it. I'm assuming that's there to prevent it from vibrating. Based on the caps I've replaced so far, these things have shrunk considerably in the 40 or so years since this thing was manufactured, so there's about zero chance I'd be able to get an identical replacement for the large power cap. This is the sort of thing I want to be sure I don't bung up as I work through this beast.

So yeah, short novel, but that's what I'm dealing with. Any input or suggestions would be appreciated. In an ideal world, I'd like to see this Sony come out in better shape than I received it, so the more knowledge I have going in, the better!

 

There is a post on audiokarma by a tech who did a complete tune up on a Sony STR-6800 SD, including pics and a list of parts replaced, and what components he replaced them with. If you do a google search on recapping Sony STR-6800 SD
the first listing should be on audiokarma. Look for the 3rd result or so down titled Restoration and Upgrade of Unican Eric's Sony STR-6800SD. Good luck!

 

Much appreciated. He seems to be venturing into territory that I'm unlikely to approach (i.e. subbing in components that don't match what's already in place) just due to my lack of deep understanding, but still good to be able to reference someone else's work.

If nothing else, I'm very pleased to realize how good the condition of my Sony is compared to the one he worked on. Bulging caps and heat damage from poor circulation in that unit. I had a fried corner of a board, but once that was addressed, the thing more or less worked normally barring the odd hiccup here and there.

 

Replace the coupling capacitors (usually 10uF) with ELNA Silmic II. These sound good sounding for an electrolytic type. The 'monster caps' are the easiest to replace and should be upgraded to new.

 

The large filter caps are clamped to keep them physically in place. Larger and heavier components can not rely on just their solder connection to keep them secure. The clamps and/or glue also help to keep vibration down. The filter caps on many vintage amps/ receivers are high quality, and do not necessarily need replacement. Look for any physical signs such as leakage or swelling. If the amp idles quietly, without any hum (nothing plugged in) the filter caps do not need replacement. As suggested, the coupling caps more often go bad. These should be replaced.

I am sorry about using deoxit on the pots. There isn't enough information online (yet) warning against using deoxit types of products.

The oil preserver contains conductive additive. This alters the values of the pots, and potentially alters the sound of your receiver. Moreover the trace and wipers were probably not oxidized in the first place (why assume they are?) but only a miro-film deposit of resin naturally dispersed in the air, and dust. The acid in deoxit introduces a corrosive chemical that permanently bonds to the molecular composition of the pots and switch contacts. (not good) This can not be undone, pending perhaps a neutralizer product and flush to remove the conductive preserver.

Also important to know, the wiper and trace of any high quality pot are self lubricating, and must make intimate contact. Oil isn't necessary, and acts as an insulator.. Lubrication of a pot just isn't a good idea.

In the future, I recommend regular contact cleaner, short bursts, work the control ....wait.... then repeat. Do not "fire hose" the pot, as this washes out the lube on the shaft bearing and this displaces on the wiper and trace (also not good) If over-flushed, the original damped action of the pot will also be diminished or completely gone.

One needs to know what they're doing. Even (some) techs are not hip on how to properly clean pots and switches.

The belief in deoxit is a modern cult. There are those who swear by it. Just allow a few more years, or a decades and see what happens to those valuable vintage parts ceremoniously ruined by this product- just getting the word out! (the "believers" will say, "spray more deoxit, it works great")

Sorry about this bad news post!

 

30 years is considered time to replace caps. Yes. I had 50 year old caps performing well

 

Yea, this is one of the main problems when restoring vintage gear, the electrolytic capacitors are much different now, the aluminum plates are super highly etched as a result of technology advancements, and the result is very thin and brittle plates with a very thin paper separator, and the cases are drawn much thinner and more brittle too, which means the size can be much smaller. But that means the forces are concentrated in a smaller, lighter, stiffer, and much more resonant package, and they generally sound much worse than their much more massive vintage counterparts. And the leads are typically steel to aid in pick and place operations. Many of the larger electrolytics of old also had generous amounts of tar-like damping substances inside.

In any case, there are some companies that specialize in supplying vintage-style capacitors to the restoration industry, so all is not lost. And many people prefer the more modern capacitor sound, so there is that too, though I can't imagine why, they are mostly more harsh sounding.

 

Get Nichicon LKG series III with gold solder contacts. These are audio grade available in two sizes in each capacitance size. These will not have any negative effect on audio quality sound.

 

Here's where I start to sound like an idiot bashing rocks together...

Which caps are the "coupling capacitors?" So far, I've been working off of the circuit diagram, but it's very tentative stuff I'm doing. Basically, I'm trying to match up any symptoms I'm experiencing with the likely board and then identifying the values of the components in that section of the circuit. The specific roles a component may be playing in the circuit are a bit lost on me beyond what the service documents offer up (Power Amp, EQ Amp, etc.).

Oh, and so I'm clear on this, my current "gremlin" involves periodic outages from the speakers. Usually, the right channel is the one that gets dodgy on me. The signal gets "fizzy" for lack of a better word and sometimes cuts out. This is usually rectified by wiggling the knob that controls the EQ pre-sets (presence, et. al.). It may not even be that the knob is relevant to the problem and it goes away on its own, but I've noticed that I'll have some days where the receiver performs completely normally and others where I have a few instances of that channel irregularity.

As of the moment, more thoroughly cleaning the pots and re-capping the EQ Amps are my best idea. The larger question of re-capping the whole machine is mostly down to the age of all of the components rather than down to any visual damage or imperfections. Even the capacitors I have replaced, near that burnt out corner of the power board, were not bulging or visibly damaged in any way I could see before they were removed from the board. Once removed, there was obvious singeing on the sides of their casing.

Thanks for the tips.

The filter caps don't show any sign of bulging or damage and there's no real hum from the unit at normal listening volumes. I'm not sure if it's related, but there IS a periodic vibration that can be felt from the metal front plate. If I place the back of my hand lightly against it, there's this constant almost buzzing vibration. It's not audible and doesn't seem to correspond to the music. Being perfectly honest, I thought I was being low-level shocked by the receiver when I first noticed it, but there was no arcing or muscle twitching, so it seems to be a conducted vibration. Here's the funny part: after sitting for a while, this vibration goes away completely. It only seems to return when the receiver is moved around, so I am left to assume some component is vibrating at a high rate, but then settles into place. Not sure which component that may be, but thought I'd mention it while we're on the subject.

I'd never heard anything negative about Deoxit, but this is all good to know. I used some very trace amounts from a nearly empty can of Deoxit red to lubricate the pots on the front panel. This was likely necessary as, while the pots weren't seized up, they moved much more freely after the limited cleaning they were given. Likewise, this also improved the issue with even playback from the two channels. Before I replaced anything in the unit, it would play much more loudly from the right channel than the left. Once the pots were cleaned, it was much more consistent barring the issue I mentioned above, which is now intermittent.

Are there cleaners that you would recommend?

How dramatic a difference is created in, say, re-capping the power circuit vs. the EQ amp? Are there makes that you'd recommend as replacements for this kind of work? I'm coming to this project in a somewhat odd way in that I have no idea what this receiver sounded like from the factory. I enjoy its sound now, but have no idea how much that has been affected even by the work I've done so far. Because I'm not married to a sonic characteristic from this amp, my main goal is doing solid work and putting good components in to create a decent piece of hardware.

Incidentally, though I don't know the series, I replaced the old Nichicon caps with new Nichicon caps. How particular do I need to be about which caps I select beyond picking a good brand?

Again, sorry if this is all remedial, beginner stuff. This is my first go-round with this kind of work. Most of my soldering in the past has been on guitar wiring, so it's a bit of a step up!

Thanks for this. Beyond knowing Nichicon was a good brand, I had no idea what to aim for in terms of caps that were ideal for audio applications.

How big of a deal will the physical size be with these capacitors? Or, put another way, do I absolutely want to replace like with like or am I fine to put in smaller caps so long as the values match?

 

A schematic would show coupling caps. It connects a transistor or op=amp to next amplifying device. There are cheap enough, use Silmic for all small capacitors. DeOxit is best terminal & potentiometer cleaner. The large caps comes in two sizes and likely to match the factory stock diameter. But, will likely be shorter in length- no big deal. I do not believe power supply large caps have much effect on the sound. I believe the rectifiers have more effect. Use fast switching low noise diodes for the power supply. The rest of capacitors do affect the sound, so use the best sounding caps. I am not steering you wrong.

 

Popular brands of contact cleaner can be found on Amazon, Radio Shack, local automotive parts stores, CRC and Radio Shack (without lube) are easy to find. Constact cleaner would also free up stiff pots just the same as deoxit does, since deoxit is mostly contact cleaner formula. The difference is that deoxit contains acid and oil based preserver with dielectric properties. As mentioned, oil is an insulator so a conductive additive assists in electrical contact in switches. This same conductive preserver (oil) also leaks voltage to ground, and alters the value of the pot, ie: a 100k pot may become a lesser value.

When deoxit works, it does so because it is contact cleaner. So, then, contact cleaner accomplishes the same result, except not the long term potential (likely) long term damage. Sometimes contacts can be oxidized. When contact cleaner fails to produce results, then use deoxit. The switch contacts were already toast to begin with, so "you get out the heavy artillery".

For everyone:
Look.. this isn't my opinion. Any acid will eventually re-oxidize the part that it cleaned. Secondly, contacts are most often NOT oxidized. The introduction of an oxidizer to "clean" contacts not oxidized doesn't make sense, does it? Please refer back to my original post, contacts most often are dirty, adhered dust stuck (stubbornly) on deposited natural airborne resin, this resin in very small amounts in regular air from the great outdoors, cooking smoke, etc. This residue is NOT oxidation. Over time the resin accumulates as a very thin micro-film, and dust sticks on this. (Contact cleaner displaces it or removes it) The OEM (original equipment manufacturer) pots and switches of any receiver are unique and almost impossible to replace, except by the purchase of a parts unit not subjected to a tech with a can of corrosive deoxit.

 

Two observations really. First I absolutely agree with either Elna Silmic or any of the Nichicon capacitors - particularly the signal level bipolar ones (ES series), which have exceptionally low harmonic distortion. Both types are surprisingly cheap for what they are.

Secondly, I have done tests on leakage of Deoxit D5 and G5 (assessing their suitability in test equipment that needs superb isolation from ground). Contacts were placed 5mm apart on a perspex plate (screws and bolts). Sprayed liberally with Dexoxit, and then tested with a meter capable of measuring up to 10^13 ohms with 1kV applied. The resistance was greater than 10^13 ohms (ie greater than 10,000G-ohms) at 1kV, both when still wet and then after the film was dry. So it simply cannot cause leakage paths within a pot to reduce its value, plain and simple.

And what is your evidence that it is acidic? You might have been fooled by the fact that it probably contains oleic acid - which is actually not acidic. It is what is called a fatty acid, and is non-polar, hence cannot be acidic. The term acid comes from the fact that the carbon chain terminator is COOH. But in the case of unsaturated fatty acids (like oleic) it is strongly covalently bonded, and does not give rise to free acidic radicals. And anyway it is not soluble in water - and hence cannot be acidic anyway. In fact it is part of a normal human diet. It is related to fatty acids in butter and butter spreads and cooking oils - which clearly are not acidic. Omega-3 is a fatty acid - same thing, not acidic.

If you are absolutely determined that standard Deoxit D5 and G5 are bad for a pot, in spite of the facts, they do a specific product called FaderLube (or F-series) and FaderGrease intended for things like mixing console faders, but is equally good for rotary pots.

 

Thanks for your response. I need not show evidence oleic acid is an acid. (it is an acid which reacts with base materials as per MSDS warnings) If your testing showed open resistance across 5mm, then perhaps the formula you tested does not contain any conductive additive. This is a two edged sword. Oil is an insulator, therefore any oil preservative on contact points will tend to inhibit full electrical contact. Dielectric across contact points can not be a good thing.

 

Such nonsense.

Oleic acid is not an acid that reacts with bases. The term oleic means that it is derived from olive oil - you trying to tell me that olive oil reacts with bases? Do you seriously believe that omega-3 (also a fatty acid) present in oily fish like salmon and tuna is an acid that reacts with bases? That fatty acids in the spreads you put on your bread are acids?

And where is the MSDS sheet for Deoxit that shows that it is acidic, precisely?

I'm finished arguing the toss with you on this FRiNgE. Unless you have specific and scientific information to contribute rather than uninformed opinion.

 

The first thread I've ever read or seen that pisses on DeOxit!
I've used it for years with no problems at all, let alone acidic or corrosive!
There are heaps of electronic repair people that use and swear by it too.
I'm very happy with the product and had No failures from using it.

 

FWIW: I have read a number of places never to use deoxit on potentiometers because it has been claimed to damage pots. This is what Caig makes a product called fader lube for. I have never tried any Caig product on pots yet. But I do plan to try fader lube one of these days. I have always felt safest using a zero-residue cleaners which state that they are completely safe on plastics.

However when it comes to switches, I spray liberal doses of deoxit into those regularly with no ill effects.

 

Been a while since I posted this thread.

For a while, the receiver was behaving, so I was inclined to leave well enough alone (though I was still familiarizing myself with the layout of the boards and the schematics).

Where things stand now, I've taken the highly technical and advanced step of replacing the festoon lamps in the front panel, so it actually LOOKS powered on now. I know, I know. Hold your applause until the end, please!

Actually, Even that opens some repair possibilities on this Sony. The lamps to the sides of the radio "dial" had actually cooked off the colored coating on the sides of the glass running across, so where it would have been a vibrant green off of the factory floor, it's now spotty green bordering on white in some spots where what I assume was intended to be a light filter is most damaged. The logic of putting incandescent lamps in a tight metal enclosure is a bit lost on me, I'm afraid...

Yes, I'll probably be looking at sourcing or creating colored LED replacements that I can slot in. The lack of heat and the ability to sub in colored bulbs rather than "repair" the glass (assuming it's even possible) are distinct entries in the "pro" column for that idea, even if I gather it's a bit of a royal pain to assemble something like that.

As for the caps, I've yet to take any additional steps - mostly because I really want to avoid modifying the sound. An additional round of pot cleaning (don't worry, I didn't drown the things) addressed any channel dropout i was experiencing, so that symptom I'm considering resolved. Unfortunately, the protection circuit randomly clicks on and off some days. Funny enough, this seems to be connected to humidity and/or barometric pressure.

What I'm leaning towards at this point is a full re-cap of the power protection board. It's the board where I replaced the cooked components from one corner, so it's not unthinkable that other components are failing, just not as visibly.

I did hit a wrinkle on something discussed up-thread. The large filter cap is actually a two-in-one component, which I don't believe I can source a direct replacement for. It's a Nichicon "Dual-C," which each "half" rated at 1000uF, 63W. There are three rather large solder pads under it: positive, negative, and ground. In theory, it would be possible to replace it with two individual caps with the same rating, but I'm unsure of how easy a time I'd have fitting two caps into the space it currently occupies or even if it's worth messing with that component since the receiver idles quietly. Curious if anyone else has dealt with one of these beasts. I can't even find used components of this type on EvilBay pulled from working units, so I'm going to go ahead and guess that it'd be quite the hunt to find one NOS or something.

Anyway, all that serves as an update on the (mostly mental) process.

 

You can buy tall & narrow caps that two will fit where the original was installed. New is 12.5mm x 40mm.

 

I don't repair amps for either a hobby or a living, so let's start there.

I do agree, that most of the time, pots are not oxidized, but rather have accumulated junk that was in the air.

When in doubt, I always use alcohol to clean most electronic's. It is a good solvent and it evaporates.

I have known many experienced technicions that refrain from using DeOxit, which is good enough for me.

It is apparent, that DeOxit contains a cleaner, what else it might contain, remains a mystery to me.

Another good, effective cleaner is hydrogen peroxide, as it is not acidic. We use it at the motel to clean the coils and other parts of the window air-conditioning units with, for that reason.

The problems with many commercial cleaners is that many leave a residue, which is not good.

They also, may contain additives to "improve things". As an example, people will use photo flow as a wetting agent in DIY record cleaning solutions. If you put too much photo flow in a film negative after processing, if will leave a film. Once these films have dried, they can not be removed.

Another thing that photo flow does is to include a lubricant in the film negative, which helps keep it from drying out and becoming brittle. There is not real need to leave this behind on the surface of a record.

One of our members recently commented that records may be noisier after cleaning than before. This is because the gunk in the groves also can serve as a record lubricant. Thoroughly clean it and the "lubricant" is no longer there. I believe that the analogy was made making the comparison of a freshly cleaned record to a freshly cleaned piece of glass, that is "squeaky" clean. It "squeaks" because of the friction that is created, when running your finger across the surface, due to the friction of your finger against the clean piece of glass.

So there are manufacturer's who put "lubricant's" in cleaners for that precise reason. To reduce friction and to allow something to operate more smoothly.

Lubricants tend to be oil based, which in an electrical circuit constitutes an dielectric, effectively acting as a insulator to and adds capacitance to an electrical circuit. But, when added to a pot, will allow it to rotate more smoothly. That is what the customer would be expecting when receiving back a component to be cleaned and serviced, isn't it?

Put a lubricant into a commercial record cleaner, and the stylus will glide quietly through the groove. People will think, "what a wonderful record cleaner, this must be".

The problems with lubricants is that they dry out and leave a hard to remove residue on the surfaces that it comes in contact with.

Place a few drops of salad oil in a corner, out of the way. Come back a month later and see what is remaining.

Don't know. I am not qualified to address these issues, but do I need a "fatty acid" that is an oily substance as residue on my pot?

How about let's not. We can always say that we did'

Since some things can not be undone, lets strongly consider the implications of using them in the first place.

I make my own record cleaning solution (which I also use to clean my tile floor's), with the same type of surfactant used in products like photo flow, but without other unnecessary lubricants, artificial perfumes and such.

You can wash your hands with a drop or two of Triton X-100, wash them thoroughly in distilled water and if you smell your hands afterward, you will see that they are clean but there is no remaining smell, like you have when washing with soap.

Soaps and detergents will most always contain lubricants to soften and protect the skin, which is an organic substance.

This would not be needed in the grooves of a record or on the surface of a pot.

As I have a tendency to err on the side of caution, I would prefer not to have DeOxit or a similar product used on my vintage equipment.

There are many safe cleaner's out there that are safe to use, when used correctly!

Is DeOxit an acid? Don't know? But all that it would take to find out is to spray some in a small cup, like a bottle cap and take a PH meter and measure the PH.

 

What's the best manufacturer for that form factor? It doesn't look like Nichicon makes anything in that size with the rating I would need - at least according to Mouser and Digikey.

 

Oh, and sorry to double post here, but another interesting discovery I made seems worth a mention.

I was checking the pictures posted on this AudioKarma rehab thread for one of these Sony units: Restoration and Upgrade of Unican Eric's Sony STR-6800SD

Of interest to me is the fact that the power board pictured here includes a bunch of diodes which, on my unit, were replaced with wire jumpers. They look too standardized to have been after-market work I was unaware of before taking custody of the receiver, so I'm left to assume one of these is a later revision of the model. I'm curious which one and also how often substitutions like this would have been made in production runs of old receivers.

Also, it leaves me wondering if I'd be better served installing diodes in these positions or if other changes were made to the circuit rendering them redundant or counter-productive. Ah, my kingdom for a robust background in electronics engineering and amplifier circuit knowledge!

 

I thing I see a lot of guys using, is WD40.
A lot of people say never to use it, but through reading and youtube, WD40 is an excellent cleaner.
I use it all the time on potentiometers, and then i'll clean off with isopropyl and then add some deoxit
to lubricate and protect it. WD40 I found is good, but you don't wanna leave it in pots as it'll eventually
collect more dust and debris and give you even your trouble.

 

Yes it will. Many people use WD40 to lubricate locks in door knobs, which is a bad thing to do. Yes, the key will slide in and out better than it ever had before, but the sticky WD40 will attract dust and all sorts of other "gunk" that may be in the air. It will also dry out and "gunk" up the lock itself.

Instead, buy a can of graphite lubricant from the hardware store. It is the correct thing to use in keyways. It will lubricate but it will not collect gunk, not will it ever gunk up anything itself.

 

There is a community out there who are into old teletypes. Monster boatanchors which have astonishing complexity of motor driven moving parts.

One of the verboten things to do is lubricate an old machine with WD40. It basically dissolves all the old grease and oil and moves it into the deep recesses of the mechanism. And evaporates leaving tarry goo, which renders the machine absolutely solid. The only recovery is a complete and nightmare strip down, part by part clean, and reassembly. Teletypes are not my thing by the way, but because of an interest in restoring old cipher machines, I am on a mailing list to do with this sort of thing.

Now WD40 has its applications I am sure. Somewhere. But is has no place either in delicate mechanical things, or in audio components. There be dragons.