Restoring vintage audio gear

[RiRaRi]

Hello. Let me introduce myself and what i do. I buy vintage radios (solid state for now), boombox, cassette decks, walkmans etc and now i want to properly and professionaly restore and sell them. Items are made in 70s and 80s. I know how to properly lubricate each part, change belts etc. But one of the biggest issue of these devices are electrolytic caps and what to do with them.

Here is my idea:

I am planning to buy proper esr meter and i think best option is LCR so i can measure at different frequencys for some caps that can not be measured on 120Hz. The frequency that ESR meters like Peak ESR70 and Bob Parker measures at (or do they?).

All radios that i buy "works". I was thinking even if they somewhat work measure each cap in-circuit and replace the ones that are even a little bit out of spec and leave others. If few are out of spec then make full recap. Is it better in any case, even if it works replace all caps? Because the least thing i want is that customers radio begins to fail in near future but also i think full recap of working boombox from 80s is overkill. Should i just if radio is working replace big caps since they are first that begins to fail? What do you think and how would you restore solid state radios and devices? Is my approach good? Thanks

[RoGeorge]

I wouldn't change anything as long as it works.

Back then ESR was not such a big problem, particularly for audio gear that usually doesn't have SMPS or other high current pulses that will require low ESR caps in good shape.

[RiRaRi]

Thank you. Thing is i didnt start to fix them properly yet and i have full warehouse of devices haha

You already gave me usefull information so thanks
But you know how people say: working time of electrolytic caps is 30 years for commercial use and 50 for non-commerical.

I am looking for best approach. Do bigger caps fail easier? Is it better to replace few bigger then and leave others if everything works?

[Wallace Gasiewicz]

Start by reading about caps available today_
https://resources.altium.com/p/which-type-capacitor-should-you-use
By the way, you are going to have a heck of a time determining if electrolyte caps are out of spec, since the specks are extremely broad.

[RiRaRi]

Great literature. Thanks, ill read it.

Why do you think its gonna be heck of a time? I just read their specs online and check ESR but usualy if less then 1 ohm it is good and if it is more it is bad. I will check capitance and esr. I know there is leakage test too but i hope i wont need it.

[Wallace Gasiewicz]

Because the tolerances can be large and the Leakage should be  measured Also.It is in the article.

[trobbins]

Perhaps don't expect that all ecaps you see are the same, or measure the same. You indicate the equipment you want to test spans a decade or two, and you won't know how long any item will have been in use or just left in a cupboard.

Certainly try and measure esr to grow your experience, and note the make, model and era of those that show a wide range of esr within one item of equipment.  Do the same for new ecaps of the same rating, to indicate the range in values to be expected as ok.  If a cap is still ok after 30 to 40 yrs, then what does that tell you about its chances of failing over the next year or two.

[Wallace Gasiewicz]

Electrolyte caps should have some leakage, mostly in the PS. The leakage is important.  The correct amount. The PS filters work better this way. These are your big electrolyte caps mostly.In some audio applications the DC blocking caps, say between one audio amp stage and another, are electrolyte. These particular electrolyte caps should be low leakage. I have replaced some of these with newer style caps say Tant or maybe even Multilayer Ceramic. 
If you can use a multi layer ceramic, do it, they are really cheap and quite good.  But I am not a purist or an audiophoole, and cannot hear well anyway.By the way, MLCC in thru hole packages are frequently just a surface mount cap put inside a package with leads.

These AC coupling or DC blocking caps (whatever you care to call them) can go bad and can severely limit or shut down your otherwise good amp. If you are repairing these things for a little income to support your habit, it is a happy circumstance when you find that sort of fault. Easy Fix. Sometimes easy to find, they can just go short and you can see this on a multimeter ohms reading.
The blocking caps in RF sections of radios are usually ceramic and are not a big problem, usually.Some RF caps are MICA and are hard to come by. I try to pick them up at Hamfests. Mostly these are in transmitting sections, so you may not need them. They are almost "immortal" . Old ones are OK.

Restored radios usually have all the PS caps replaced, since you are dealing with transistor radios, this should not be a problem, new electrolyte caps are better and smaller.  Usually a cap of higher voltage rating is used while trying to stay close to old capacitance value.
In tube designs, restorers have been known to gut the "cans" containing the old electrolyte and hide the new caps in the old cans. Go think!
This probably should be first since Safety is First.  Use the proper X and Y protection caps (also known as line filters) on the AC input. There are lots of articles on the web and lot of references in this forum about this.

[Wallace Gasiewicz]

Oh, I forgot to include,
I think you should get a component tester for caps and transistors, like the peak or BSIDE.Worry about specific freq response later when you are dealing with Hi Fi stuff.If the component works on these cheap (but really good ) testers it is OK for audio use.Start with one of these and later see if you really need a multi freq tester.I have all sorts of cap testers and almost all of the time, a quick check with my BSIDE is quite enough.

[RiRaRi]

Thank you very much. I was planning to replace caps in power supply yes. May i ask you for model of that BSIDE?
I wanted to get proper ESR meter or LCR like DER DE 5000 for checking if caps should be replaced because they might die in the near future. Dont know should i get Bob Parker, ESR70 from Peak or proper LCR if price is not an issue. I just want to get better tester for in-circuit and out of one. But also, if Bob Parker or Peak measures at different freq then i dont think LCR is neccesary.

[Wallace Gasiewicz]

I use BSIDE ESR02proThere are some threads elsewhere on EEVBLOG discussing these things. Look around, lots of the brands are quite good.I would get a good tester like these cheap ones and a good Multimeter, you don;t need one with transistor tester since you are going to get a component tester.Since you are dealing with lots of audio, I think the other thing you will need is an OscilloscopeI THINK unfortunately that the digital scopes are not as good as the old CRT scopes for audio (gosh, I can feel the responses coming)But fortunately a cheap old CRT scope with even 10 or 20 MHz will be plenty. Make sure probes match scope. 
Ham Radio gatherings are a good place to buy stuff, I don't know what sort of flea markets are available in Croatia.You are going to need test leads, with various clips (alligator etc...) these can be expensive new, but you can pick up some used.Another thing to look for is a triple power supply, or a good old variable PS. Prices at hamfests are a lot cheaper than on line, less than half mostly.

You are going to need these things anyway, so get used to them and use them a lot before going further in your test equipment purchases, like LCR.
Also if you buy used test equipment, odds are that if you don't like it or grow out of it, you can sell it and not take too much of a financial loss.  Not true with buying new stuff.A real LCR meter is useful when you are dealing with RF not necessarily audio....one of mine tests at 1 MHz
Higher freq LCR are necessary for small capacitance and small inductance used in RF. Like I said  Later....

[RiRaRi]

Thanks for in-depth answer. First i would like to ask do i really need transistor/component tester if i have good multimeter with diode function (Fluke 179 in my case)? Is there some other things i can see on these testers that i can not on DMM that can indicate health of transistor?
Second is that i need ESR, so maybe if LCR is overkill i will get something like Bob Parker design or Peak ESR70 beacuse i need something little better and more accurate then those 15 dollar chinese component tester. I want to have as accurate reading as possible but also i heard that it is not so important because caps which are bad or will go bad in near future have multiple times of original esr. So i would change those ones that are even a little bit higher esr than one in datasheet.
Also, do you think my approach is not good? Beacuse i dont think scope is neccesary for restoring/servicing boombox, radios, cassette decks etc. The stuff that is not high-end complicated hi-fi gear. I will test each component with multimeter, esr for caps and transistors (with transistor tester?). Also i will change bigger caps or the ones in power supply even if they measures good. After that, if everything indicates of good health i consider that radio restored and working. TBH i really want to learn how to use scope but it sounds very complicated for someone that doesnt have degree in electronics and know only its basic and what each component do. So my last question is: when i am scoping do i get more indication of components health then doing it as described with other gear? It takes longer thats for sure, but is there any other advantage?

Thank you so much again for helping. This conversation will really benefit me and my work

[chilternview]

Also i will change bigger caps or the ones in power supply even if they measures good.

There's an old saying, "if it ain't broke don't fix it". And that applies to repair work; why change a cap unless you know it's causing a malfunction (or is imminently likely to, for example leaking electrolyte or showing signs of bulging). Of course a DE5000 or similar is a good investment if you take this up seriously, but it's not essential at first.

You mention you want to buy, restore and sell gear. You will be eroding your profit margin if you needlessly replace all the electrolytics that are not quite in spec.

I volunteer for a repair cafe and of the electronic goods that we get for repair, I'd say well over half the faults are mechanical.

[coppercone2]

replace caps on a basis of how easy they are to replace. If something is a PITA to access and you need to access it to repair something and then you end up like redoing a bunch of wires then replace everything so you don't have to go in there again. If its easy access you can save money.

I had good caps look anywhere from brown to new inside for the spraque electrolytics.

I found that some designs are so terrible to open up and also clean flux off of, that it just made sense to replace everything I could at one go.

Like even from a repair service prospective, if you are going to be the guy that fixes the gear in a while when people return it, it just makes sense to get rid of PITAs at first opportunity.

Mr carlsons lab on youtube is rather... greedy when it comes to components, you can save money using those methods of testing,.