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-   -   Akai GX77 recap - which ones to change if any? (https://www.vintage-radio.net/forum/showthread.php?t=175278)

Andrew64 14th Jan 2021 8:24 pm

Akai GX77 recap - which ones to change if any?
 
I have been asked to recap an Akai GX77.

The machine is early 80s and all works, I've checked the capstan motor commutator and other wear points so know hours run are low.

The majority of the caps are Nippon Chemi-com, mostly black with some orange and yellow ones. There are a sprinkle of Marcom ones which I believe are a subsidiary of Nippon Chemi-com.

Now my question is, is it worth replacing all the caps, only some or even none?

If only some, would those in the audio paths be the ones to go for?

Lastly is there anything else that would benefit from a change?

John_BS 15th Jan 2021 8:43 pm

Re: Akai GX77 recap - which ones to change if any?
 
There's an awful lot of them, and there's the risk of collateral damage.

I'd recommend removing a respresentative sample* and testing them. The ones which tend to be critical are coupling C's which feed into a high impedance (c. 100k ish ) where any leakage current may upset the DC conditions. Check those for leakage at the approximate working voltage.

If they're OK, leave well alone.

John
* e.g. C10, C33, C39

DMcMahon 16th Jan 2021 8:13 am

Re: Akai GX77 recap - which ones to change if any?
 
Definitely concur with above, do not replace all the capacitors, a huge job with high risk, very few if any may actually require replacing.

Recapping (as a full blown exercise) generally refers to coupling/de-coupling paper capacitors normally found on some older valve equipment, some Electrolytics and some Tantalums.

David

stevehertz 16th Jan 2021 8:44 am

Re: Akai GX77 recap - which ones to change if any?
 
It's an 'american' phrase/word; recap. They do it because it has become de rigeur, fashionable even to recap any item of vintage hi-fi. Over there there are many specialist vintage hi-fi technicians who make a living out of wading through amps, receivers, tuners, cassette decks etc changing every electrolytic cap in sight and furthermore claim that it is necessary. Given the good living they make out of the practice, a cynic may say that it's biased advice.

Now, to me. I collect and restore vintage hi-fi and I like everything to work perfectly. After normal restoration, when in terms of electrolytic caps I may have had to change the main smoothers due to leaking and hence faulty, I have very rarely had to change any other electrolytics. I've probably changed more transistors and resistors than electrolytic caps! And to my highly critical ears everything works and sounds perfect. In the UK we do not suffer from extremes of temperature like they do in the US, and I'm sure this helps with the longevity of caps, heat kills them. Similarly, in the US they generally push their equipment harder/louder in bigger rooms and use much higher powered amps and receivers that similarly generate more heat, leading to failure.

Your cassette deck is working fine, leave as is is my strong, experience based opinion. Just explain to the customer that recapping is an American obsession that may have some justification in a hot, dry country but over here it's not necessary and is no more than a borrowed, misguided vintage hi-fi fashion.

Uncle Bulgaria 16th Jan 2021 1:41 pm

Re: Akai GX77 recap - which ones to change if any?
 
Quote:

Originally Posted by Andrew64 (Post 1330851)
The machine is early 80s and all works, I've checked the capstan motor commutator and other wear points so know hours run are low.

I'd let that be your guide. If nothing's wrong, don't fix it until it breaks! If it's for a customer, either they'll accept the engineering advice that nothing needs doing to it; or if they insist then you'd have to charge a convincingly gigantic price for the great labour of doing so.

Besides, there's a lot of nonsense written about 'capacitors in the audio path' which I think comes from America, in the same vein as stevehertz's post. When one stops listening to the music, some imagined niggle of dissatisfaction means money must be spent on changing hardware, or taking tiny measured differences in radio frequencies and believing there's an audible result.

If that comes on strong, it's because I've made the mistake of fixing something tiny until it breaks. Shipwright's disease is debilitating! ;)

stevehertz 16th Jan 2021 2:22 pm

Re: Akai GX77 recap - which ones to change if any?
 
You me both Uncle. Lotta rubbish and 'guilt' propagated by inveterate cap changers. The 'improvements' they supposedly hear and the blind faith levels of belief they have in recaps are borderline audiophoolery territory.

Welsh Anorak 16th Jan 2021 2:32 pm

Re: Akai GX77 recap - which ones to change if any?
 
Totally agree. The only exception may be the capacitor fitted across the mains input. These can and do deteriorate with age and can be replaced with a more modern class X2 component. However, if there's one fitted to your machine it's likely to be a Japanese part which are usually reliable.
I see there's a kit available online with 59 capacitors! I would be very reluctant to replace all - or even some - of those as even experienced restorers can make a mistake and we've all had that 'why did I start?' moment. Maybe take out and test a sample as suggested above.
It's a lovely machine and as most capacitors are in the small signal path and of a good make they are unlikely to have deteriorated much if at all.
Far better than random capacitor replacement is a good old mechanical service. Then the best test is your ears - if it sounds good then enjoy it!

ms660 16th Jan 2021 2:34 pm

Re: Akai GX77 recap - which ones to change if any?
 
Each time you take something apart you increase the chances of introducing another fault, sometimes it's best to replace all of a certain type of component in one service if you want long term reliability and good feedback from paying customers.

Lawrence.

DMcMahon 16th Jan 2021 3:08 pm

Re: Akai GX77 recap - which ones to change if any?
 
Quote:

Originally Posted by stevehertz (Post 1331277)
.

Your cassette deck is working fine, leave as is is my strong, experience based opinion. Just explain to the customer that recapping is an American obsession that may have some justification in a hot, dry country but over here it's not necessary and is no more than a borrowed, misguided vintage hi-fi fashion.

Reel to Reel not cassette.

David

Ted Kendall 16th Jan 2021 4:06 pm

Re: Akai GX77 recap - which ones to change if any?
 
Quote:

Originally Posted by Uncle Bulgaria (Post 1331363)
If nothing's wrong, don't fix it until it breaks! If it's for a customer, either they'll accept the engineering advice that nothing needs doing to it; or if they insist then you'd have to charge a convincingly gigantic price for the great labour of doing so.

Besides, there's a lot of nonsense written about 'capacitors in the audio path'

Quite agree.

ben 16th Jan 2021 5:30 pm

Re: Akai GX77 recap - which ones to change if any?
 
Don't get me started on this capacitor nonsense. I have ended up avoiding participating in several US forums I used to use regularly because of the moronic obsession and unscientific positions found there in this regard.

A surprisingly large number of people over there seem to think that the capacitors needed to be changed 'for reliability' because they're 'old'. The response I adopt is: if you're going to do that, then why stop there? What about all those old resistors, pots, transistors and other semiconductors of the same age? No logical responses were forthcoming! ;)

Of course, as always there are shades of grey and exceptions. Caps in audio do not lead anywhere near the hard life you find in enclosed SMPS or high voltage equipment like TVs. But there are caps that are known as problematical: Rifas and the wax types; the red/black plessey electrolyrics... There are others that have seemingly given many people problems such as the gold frakos (though I only ever saw that once on a Uher r2r) and tantalums. Then there's the 'badcaps' plague of a few years back which I suspect is responsible for originating a lot of this nonsense.

But of course, it just comes down a proper servicing 'approach'. The internet is now full of the non technical who do not use a meter, or even deductive reasoning and fault finding techniques, yet churn out their 'advice' to others who then perpetuate the same thing and so the cycle continues!

In this case, if there's no hum or loss of signal, leave well alone.

stevehertz 16th Jan 2021 5:57 pm

Re: Akai GX77 recap - which ones to change if any?
 
Quote:

Originally Posted by DMcMahon (Post 1331398)
Quote:

Originally Posted by stevehertz (Post 1331277)
.

Your cassette deck is working fine, leave as is is my strong, experience based opinion. Just explain to the customer that recapping is an American obsession that may have some justification in a hot, dry country but over here it's not necessary and is no more than a borrowed, misguided vintage hi-fi fashion.

Reel to Reel not cassette.

David

Ok, thanks for pointing that out. Still of the same opinion regarding recapping.

TIMTAPE 16th Jan 2021 11:17 pm

Re: Akai GX77 recap - which ones to change if any?
 
Hum in an audio device is often a sign of a failing electro. Another is weak bass.

Andrew64 18th Jan 2021 11:40 pm

Re: Akai GX77 recap - which ones to change if any?
 
Thank you all for your suggestions, there is a lot of knowledge on this forum that I am most grateful for!

I personally am not in favour of wholesale recapping, particularly a difficult deck such as this. That is why I sought help to clarify my mind.

I have done a cap and trimmer change on my Revox A77 but as 10 caps were duff and itís not a hard deck to do I was happy to do it.

A problem of wholesale component change is, as John mentioned, collateral damage - so easy to do.

In view of this and various points contributed I am going to check the frequency response and various caps then make a decision on how best to proceed, Iíll keep you posted.

dave walsh 19th Jan 2021 12:50 am

Re: Akai GX77 recap - which ones to change if any?
 
You clearly know what you are doing Andrew [which is more than I can say:D] but the reaction here illustrates the strength of feeling. No one seems to quite know where this "change all caps" notion originated except it's probably American and clearly relates to engineers who have such a regular through-put [as mentioned] that they can be totally confident they won't make things a lot worse or can sort it out if they do! It's become a sort of accepted truism which it isn't at all-especially for amateur restorers. It's a form of wishful thinking in a way I suppose if, like me for example, you don't have the experience!

Surprisingly this takes me back to the first vintage Popeye films when he is very upset and releases all the the animals from cages in Olive's Pet Shop. Only the wise old Parrot refuses to leave a perfectly comfortable and satisfactory existence.
He sings the great song- Leave Well Enough Alone!
"I know me stuff and I'm smart enough to leave well enough alone!"
[Of course a sense of humour may be required8-\

One of the much later Hunikun Technical TV series episodes has him stripping
down a van with a funny noise. He doesn't sort it and concludes it's better
just to leave things alone some times!

Dave W

Ted Kendall 19th Jan 2021 8:56 am

Re: Akai GX77 recap - which ones to change if any?
 
Quote:

Originally Posted by dave walsh (Post 1332245)
No one seems to quite know where this "change all caps" notion originated

I think I first heard of this in connection with refurbishment of studio desks, where there are many capacitors in the signal path of each channel, densely packed and running up to 24/7 for a decade. This would have taken enough of the electrolytics beyond their design life to justify wholesale replacement, on grounds of reliability if nothing else - and at the time there were the budgets available to do it. Enough of the audio fraternity took the headline away and pronounced it a panacea, without understanding the background.

Of course there are cases where it's sensible just to do the lot - David's (RW) Revox tuner which had spent many years roasting in a rack is a good example, as are Fostex G series multitracks, where the failure rate is woefully high - but most domestic semiconductor-based kit is best served by replacing faulty capacitors and letting the rest be.

Nickthedentist 19th Jan 2021 10:30 am

Re: Akai GX77 recap - which ones to change if any?
 
Quote:

Originally Posted by Ted Kendall (Post 1332269)
...most domestic semiconductor-based kit is best served by replacing faulty capacitors and letting the rest be.

Yes. An exception perhaps being that if you find a fault caused by a failed electrolytic capacitor, it's sometimes reassuring to replace any "similar" ones at the same time, e.g. the LH speaker coupling cap if the RH one has developed high ESR; or the other Frako 10uF 25V caps if you've just had one that's gone s/c.

I'm also suspicious about ones that live right next to hot-running components. And those horrid SM ones which leak corrosive stuff. And Callins ones.

But the rest I'd leave. Not least because the original components (especially if Japanese) may well have been of better quality than that available nowadays.

Ted Kendall 19th Jan 2021 10:35 am

Re: Akai GX77 recap - which ones to change if any?
 
Fair comment.

Andrew64 19th Jan 2021 2:39 pm

Re: Akai GX77 recap - which ones to change if any?
 
The mention of Frako reminds me of s/c 470uf 25v one I had to change in my Grundig Satellit 3400. I won't complain though, it ultimately resulted in me getting it as a none worker for just under a ton, it was cosmetically almost perfect and came with the case & booklets as well. Must post on that sometime.

The Peak ESR70 meter I ordered has just turned up so can check those caps now…..

Welsh Anorak 20th Jan 2021 4:09 pm

Re: Akai GX77 recap - which ones to change if any?
 
Not sure if this is a granny/eggs comment, but I do recommend retesting the machine after every replacement. It's all too easy to change a handful of parts and be greeted with a fault that wasn't there before!

stevehertz 20th Jan 2021 4:53 pm

Re: Akai GX77 recap - which ones to change if any?
 
So true. I recently needed to change a few electrolytics in a hifi receiver that I'm restoring. And yes, I put a couple in backwards. The darned negative arrow strip subliminally making me think it was the positive. I've been a qualified electronics engineer for 50 years and have been restoring equipment for 40 years, before that an electronics test engineer. So yes, 'measure twice, cut once' - it applies to changing electronic components too.

knobtwiddler 22nd Jan 2021 10:22 am

Re: Akai GX77 recap - which ones to change if any?
 
Part of the recap obsession could be due to the ubiquity of Frako (lots of pro gear had them - even Neve and Studer). They often leak a green gunge which is difficult to remove. At the same time, they lose capacitance, leading to LF roll-off in series coupling circuits. I tend to replace all Frako on sight. But I have a temperature-controlled rework machine, as well as a bank of analysers. Few sights are more disturbing than a bodge recap, with the delaminated pads it inevitably involves. I tend to be quite liberal with recapping, as the unit will often be apart for other work (new pots for example), and I might as well do the caps while it is in pieces. But I agree that, particularly in the case of Japanese brands such as Rubycon, the caps can go on almost indefinitely.

knobtwiddler 22nd Jan 2021 10:28 am

Re: Akai GX77 recap - which ones to change if any?
 
And another thing: changing out Frakos can stop pots rustling (DC). Tants are the worse in this regard. A tant that is over a certain age should always be swapped for a modern low-Z cap. Pro gear can have a lot of pots, and coupled with 40 year old Frakos and tants, it doesn't take a lot of detective work to see why studio engineers are finicky about new caps.

Welsh Anorak 23rd Jan 2021 1:02 pm

Re: Akai GX77 recap - which ones to change if any?
 
Absolutely right - you don't want pro gear to be off the road or performing less than perfectly.
However, for domestic and semi-pro equipment common sense needs to be used. Older Hunts or Callins parts are almost guaranteed to be faulty, but later Japanese capacitors in small signal locations were pretty indestructible. In fact when I've checked I've often found the ESR of the old part to be better than a new one out of the drawer.
I think we're agreed here, and despair the attitude that if you change all the capacitors in any piece of equipment all faults will magically disappear!
With experience you get to know which to change and which to leave alone. In the OP's case, there will be very little to change.

Andrew64 24th Jan 2021 11:58 pm

Re: Akai GX77 recap - which ones to change if any?
 
Good tip Glyn, before I started work testing caps I did a level/frequency test check on the channels with sig gen, meters and scope. Input to output with source selected was fine but with tape selected and recording, the right channel level decreased as the frequency was increased, this only occurred in the forward direction, reverse direction was acceptable. I have to say though, by ear, a prerecorded tape sounded OK but my ears are old.

This was traced to the azimuth of the forward record & playback heads not being aligned. I have to say it is not that far out as finger pressure on either head is enough to correct the allignment. However I adjusted the playback head azimuth screw only to correct this, playing a prerecorded tape seems to indicate this was the correct choice as the highs seem the same for both channels forward and reverse, I will have to obtain a suitable test tape to do a proper alignment. As record & playback seem OK I do not expect many if any defective caps

Andrew64 26th Jan 2021 11:42 pm

Re: Akai GX77 recap - which ones to change if any?
 
I have checked all the caps on the power board and a selection on the SYSCON board with the ESR70 and no problems found, bit of a tight squeeze but you can just get at the back of the boards without removing them.

For the main board I magnified the board layout diagram so it needed 3 A4 sheets, I then carefully cut and sellotaped them together aligning the tracks/components carefully. I highlighted the transistors and caps with different colours and added cap values.

It took a bit of time but made life easy when it came to checking them, again board not removed, round one edge is tight due to overhanging metalwork but you can just about get to them all. Checked with the ESR70 and for the caps where leakage is critical I measured the volts across the relevant resistance loads, audio transistor voltages were check also and happy to say no problems found, not unexpected as it all works.

So I am happy to report back to my friend cap changing on this would be a pointless exercise, just need to get hold of a calibration tape now, I put a ‘want’ up for one but no joy as yet.

Welsh Anorak 27th Jan 2021 1:48 pm

Re: Akai GX77 recap - which ones to change if any?
 
I assume your friend was the victim of the recapping mania we've been discussing? You can now give him the good news. A few drops of oil and grease will be beneficial - and do check the capacitor that may be across the mains - your annotated diagram will instantly tell you if there's one fitted.

Andrew64 28th Jan 2021 11:27 pm

Re: Akai GX77 recap - which ones to change if any?
 
I have replaced a cap! There was a 250v AC one across the mains switch, I have replaced that with a Y2 400v AC one to be on the safe side.

Thanks for the hint Glyn, I have also oiled and greased, took the loading mech apart to do a thorough job, I’ve seen them play up before.

I have explained all to my friend and he is perfectly happy now I have not done wholesale replacement!

djmk1988 16th Feb 2021 9:18 pm

Re: Akai GX77 recap - which ones to change if any?
 
Although Akai didn't use hi-end capacitors in their machines, they seem to have preserved much better than hi-end capacitors on much more expensive machines. I've got pretty much all the big advanced Akai's and a couple of little gx77s (my only 7inch Akai reelers) and never had any problems with them. Only a few years ago the spark suppress capacitor for the power switch on our family's old gx635D went up in big smoke, so that capacitor is probably worth chancing as it tends to go short circuit/explode in smoke. It's the same type of capacitors they used for spark suppression in Revoxes and Studers. So my personal advice is unless the customer definitely wants this done on his deck, to keep away from it as they'll work well for another few years


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