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.

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.

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.

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.

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

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.

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.

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!

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