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NAP 160 puzzling cap explosion...

So, I was right, it's only taken me 3 afternoons to do the second one, now I've got a routine going. All well and happily brik driving, so just one more to do:


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Although - It also occurs to me that I've no idea whether my Hicap has ever been serviced... hmm.
 
A Hicap is very easy to service : two large reservoir capacitors to unscrew and a handful of tantalum capacitors to replace. Don’t really need to unsolder any wire if you want.
This one has an Avondale TPR4 but a stock one will be similar :

 
Funnily enough, I'd been eyeing up the Avondale TPR boards... Need to take the Hicap out of the system and check it over - at the very least the power LED has packed up, so that needs sorting (especially now I've replaced the neons in the 160's switches). Also glad to see it's not just me who organises their workbench with empty yoghurt/ice cream tubs etc.!
 
The LED packs up because the series resistor is buried underneath the Helsyn sleeve. It's clearly visible in the pic above. You just need a 1/4W 3k3 resistor to replace it.
When I serviced these I always did that as a matter of course. I also tie-wrapped some insulation around the input socket and fuseholder as well as insulating the mains switches to modern spec.
 
Well the good news is that all 3 NAP160s are now finished and working... the bad news is I've not yet opened up the Hicap, as when I swapped it out with my SNAPS (modded AFAIK to dual rail - normally it happily powers my Naxo 3-6) I got a ground hum, so had to keep the Hicap in to check the last NAP was ok. More investigation tomorrow, I guess...
 
So further investigation has been done, and I'm still at a loss as to why the SNAPS doesn't pass signal to the amps, just a buzz. Opening it up I can't see anything obviously wrong, although it is non-standard inside. On the subject of the Hicap, I'm suspecting that it hasn't been serviced - anyone able to tell me what denotes the date on the black Sic-Safco reservoir caps?
 
On my caps, this is the 5th line, first number is the year, second number is the week.
These as per below were made in 2010, 20th week of the year :

 
Thanks Gervais, looks like the caps in mine are the originals then - the label's slightly different, but looks like 30th week of 1987, which would seem right for a 1988 serial no. Time to go cap shopping again...
 
smee said:
So further investigation has been done, and I'm still at a loss as to why the SNAPS doesn't pass signal to the amps, just a buzz. Opening it up I can't see anything obviously wrong, although it is non-standard inside.
Click to expand...

A picture would be good, but bear in mind that the SNAPS isn't wired like a Hicap, The left two, and right two DIN sockets are wired for audio between them, but not all 4 sockets. If you have made it dual rail and added a 5 pin like the HC then unless you've also bridged the blue wires in between the middle DINs you'll only get audio out of one socket.
 
Cheers MJS, annoyingly it wasn't as simple as operator error on my part! Having taken my NAC 32.5 and a 160 down to my workshop and done some more faultfinding, the problem seems to have been that the relay in the NAC wasn't consistently closing on power up - so the NAC would appear ok, but not pass audio apart from a classic "open cable" type hum. It seems to be behaving after a lot of on-off switching, I suppose it may be prone to sticking as it's normally on 24/7? I'm assuming that either it's coincidental that it did it with the SNAPS not the Hicap, or it's something to do with the power delivery of the SNAPS (not having sufficient oomph to click the relay over somehow?)

Here's the SNAPS btw...

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It looks like the main cap has been replaced, and possibly the tants, but the bottommost resistor on the LH reg circuit has been replaced with a preset (to allow adjustment of output voltage maybe?) I'm wondering whether it would be worth upgrading the regulators to a TPR4 or used Hicap reg board?
 
Check the voltages of the SNAPS, if a rail is sagging due to leaky tants then it may not exceed the 20v zener voltage in the simple RC timer in the pre-amp output relay. If you can, check that zener and the 47uF cap too. Any of those will stop it switching reliably.

The 1k pot on the SNAPS board is to allow it to be used with a NAT101 tuner whose analogue tuning stage is calibrated for exactly 24.55v input.
Spare Supercap boards fit easily into the SNAPS - there's more than enough room to make your own TPR using a pair of them.
 
smee said:
Cheers MJS, annoyingly it wasn't as simple as operator error on my part! Having taken my NAC 32.5 and a 160 down to my workshop and done some more faultfinding, the problem seems to have been that the relay in the NAC wasn't consistently closing on power up - so the NAC would appear ok, but not pass audio apart from a classic "open cable" type hum. It seems to be behaving after a lot of on-off switching, I suppose it may be prone to sticking as it's normally on 24/7? I'm assuming that either it's coincidental that it did it with the SNAPS not the Hicap, or it's something to do with the power delivery of the SNAPS (not having sufficient oomph to click the relay over somehow?)

Here's the SNAPS btw...

​
It looks like the main cap has been replaced, and possibly the tants, but the bottommost resistor on the LH reg circuit has been replaced with a preset (to allow adjustment of output voltage maybe?) I'm wondering whether it would be worth upgrading the regulators to a TPR4 or used Hicap reg board?
Click to expand...
A TPR4 will give you a better sounding experience than a used board from a Hicap.
 
Latest update, Hicap now recapped, I went for 22000uF 63v Kemets following a trawl of threads on here, and had enough tants left over from the "Great NAP160 recapping of old '22" to do the reg board. Also replaced all the sockets with Preh's. Suspicious sticky residue around the top of one of the '87 vintage Sic-Safco's suggests this was not a moment too soon... (Oh and as per MJS's prediction, it was the series resistor that had stopped the LED working.)

The relay problem has not gone away but still only shows itself when trying to power the Nac32.5 from the Snaps, it's fine with the Hicap. Metered both PSU's and got the following:

Hicap (freshly recapped)
Rail 1 - 25.46v
Rail 2 - 24.47v

Snaps
Feed from rectifier - 37.41v
Rail 1 - 24.27v (this is the adjustable one)
Rail 2 - 23.84v

Tants don't look particularly ancient, and I've got another 10000uF 63v Kemet (like the ones I installed in the NAPs) to go in place of the 40v BHC that's in it at the moment along with more Preh socket goodness. Further investigation/tinkering will have to wait until the weekend now though, as I'm off working away for a few days.

Gervais Cote said:
A TPR4 will give you a better sounding experience than a used board from a Hicap.
Click to expand...

I realised after I'd posted, that the Hicap reg is (I think - I'm happy to be corrected) the same circuit as the Snaps one, just better executed (and fed by a bigger/better transformer with two separate outputs), so I agree the TPR would seem much more worthwhile.
 
Latest update - Acquired another CB Hicap from the classifieds on here (only 6 units behind mine serial wise) and did the same re-cap/re-socket/re-LED resistor routine. Active Brik service restored! Continued fiddling with the SNAPS, changed reservoir cap, sockets, wired them as per a hicap. Swapped 680R for 820R on the non adjustable reg to give 24.6v and matched the adjustable side. Tried it powering the NAC, only to find that whilst the LH channel un-mutes fine, the RH doesn't... until the rail (luckily the adjustable one) is wound up a bit higher (24.7 to .8v). Only then does it fully unmute, which explains why the Hicaps could do it (rail 1 on both of them is running at about 25v) but not the SNAPS. Presumably this isn't right (given the stock SNAPS voltage was 23.8v) so the relay card in the NAC is definitely the issue - do these symptoms help pin down the problem to either the zener or the cap as mentioned by MJS above?

Having been supplanted by a Hicap, I've knocked up a DIY SLIC cable and I'm trying the SNAPS in place of the NAPSC that normally powers my Headline 2...
 
I'd change both cap and Zener whilst you're in there. Fwiw my 72 unmutes quite happily at +24.0V. Naim's Zeners aren't 100% reliable, I had to change one on a 323 and did the same on the other channel as a precaution.
 
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