Ok, so actually a really confusing set of boards…!!
I can spot the 528, with its blue adjustable pot. So below that, as pictured, are two 526’s alongside each other, but these are for different inputs…? Guessing that the one in the bottom left corner would be for the Phono Input, input 1…?
Yes, a bit complicated with the swappable boards on so many inputs, which is perhaps why (as well as the arrival of the CDS) this was changed fairly early on to just having swappable boards on the phono input and straight through on the other inputs.
Hi,
i am late - you could add an “@” and search for the user name - so we (I am) are notified. 
All is said by now - older 52 with need of service.
Really like to emphasize @Richard.Dane comment - prefix is perfect for your LP12 and feeding it from 52 is preferred to feeding it from hicap.
Hi Richard, i ordered the 2 new 523k phono boards today. they will arrive by end of the month. I will have the capacitors checked upon arrival before installation. are there any photos with them installed and or instructions on how to install? thanks again for all your help.
HI Ian, i did exactly that about a year ago had both parts serviced. I did not hink to ask about the phono boards just assumed they were in there. Took some time to get my system all up and running the way i envisioned. then i decided to upgrade my 82 to the 52 and found this problem. Ordered the boards now will have them checked upon arrival then will have to install them and hopefully i will be good to go. thanks again for your help.
Carefully remove the outer sleeve (feet need to be removed) being careful not to break or chip the fascia as it can get quite brittle with age. Trace back the boards that go to the BNCs on the Phono input. Remove the old boards by pinching the lock tabs on the little white retainer that fits through the middle of the board and just gentle wiggle the boards up so they disconnect from the pins. Fitting the new boards is the reverse. Be sure that all the pins locate and that the lock tabs engage.
Unclear how you would do that…? Measuring capacitors still in circuit will not give correct results - and removing them yourself is outside the forum TOU.
The 52 seems to have been a ‘work in progress’ long after its initial release. I recall an FAQ post from your predecessor detailing some of the changes:
https://forums.naimaudio.com/topic.php?oid=1566878604356287&coid=159503632588890
Very good re-post. The key seems to be -
*** Main Board Revision 3 (latest)
From Oct 1992 (S/N 80965) links fitted in place of link boards.
Suggesting that there are 3 versions of the Main Board(s).
And more good work by @Adam.Meredith … again… 
Hi Ian, i confirmed withe seller today that these 2 photo boards are NEW and never used or out of the box. He is confident that there is no need to check anything and that they will work well out of the box. He has sold several other pairs without any issues. I am trying to get some install diagrams and instructions to install them once received. No success so far for my vintage. maybe someone on the forum has info they can share. regards Frank
Frank, see my post above with instructions;
HI Chris/Richard. thank you both so much for the education on my vintage 52. I reviewed the crono of Significant changes by S/N and my SN is 68593 so I am in the pre SN 79143 group. Which changes do you suggest i have done to my 52 to optimize the performance? Thanks Frank
These 523K boards may well be ‘un-run’, but they were not made this year…!!
Capacitors deteriorate based on time from their manufacture - not on their running time.
Bloody Annoying Facts.
Your Sellers confidence is not well founded, IMO. But YMMV…
They will likely ‘work’ - but why not get them serviced…?
Frank, yours is an early one so unfortunately it’s not cost effective to do updates such as the display board. Just don’t lose the rather lovely metal remote handset as the code set was proprietary to Naim, replacements are unobtainium, and no other handset will work with the pre-amp. The RC5 display board update was very worthwhile because of this, but was very costly to do, so was dropped around 10-15 years ago. Otherwise, a service of the pre-amp and PS would be the first priority and the POTS8 upgrade is probably the most worthwhile after that (or at the same time).
HI Richard, I received the 523k moving coil phono boards, installed them and now connected the NAIM 52 into my 6 135 mono system to replace the NAIM 82 and 2 high caps. I was up for hours last night playing my favorite Lps. The upgrade in sound is truly astounding far exceeding my expectations. I had no idea the 52 was this superior to the 82. The level of detail and channel separation is fantastic. I had my 52 and power supply serviced about a year or so ago but had no sound when i connected it into the system. Turns out the cables were fine it was the missing phono boards. Do you and others also agree there is a really significant improvement in sound from the 82 with the 2 hicaps? I could not be happier. thanks again for all your help.
Frank
Try the 82 with a Supercap it has some advantages in excitement over the Nac 52.
Yes, it is a significant step up. I still have my 82 which I used to put in to my system (with the s/cap) occasionally after I got my 52. I don’t bother anymore because the 52 is superior in every way.
I love mine in a passive system with 135’s, but in your six-pack system it should be the clear winner and sound as amazing as all the claims for it say it is. Congratulations!
If you don’t think it is better, then it isn’t.
If you don’t hear a difference then there isn’t. 
Nac 52 Nap 135 six pack was my dream system with a Linn turntable and Nak Dragon being the icing on the cake. Difficult to improve unless spending copious amount of cash imo. Definitely an improvement over the Nac 82[good as it is].
