Recapping KRK VXT6 without original datasheets

[slerner]

I'm desperate to save my pair of 2007 KRK VXT6 studio monitors, one of which died.
Hoping for an easy fix, I bought a pair of new-old-stock replacement main boards. I installed one & it was DOA. Tried the other, also DOA. I suspect that 15 years in a Maltese warehouse dried out the electrolytic caps. I tried replacing just the two largest caps, which didn't help. Except to confirm that the old ones wouldn't reach infinite resistance & were a gram underweight.
Q: How do I match the caps, since there's no series marked on the originals and no circa-2007 catalog or datasheets from the mfr TWBOR? I've wrung the web dry over this (wayback archive, patent office, digikey parametric search, ebay, stack exchange)!
I also plan to recap the little “switch” board, too. It runs the status lamp & toggles for auto-mute, ground lift & overload handling (warn, ignore, limit). Its 4 caps have 8080808 printed on them. This corresponds to nothing.
So I'm faced with recapping these boards, based solely on the marked voltage, capacitance, temp rating (all 105c) & physical dimensions. Can someone guess their functions from the pics & tell me at least generally what specs to look for, beyond what's printed on each cap? I don't have a schematic. Nobody seems to, it's been sought here & elsewhere. FWIW: this is a bi-amplification board (30 watts tweeter, 60 watts woofer, 1 mains transformer).
Or better yet, if you've successfully recapped a KRK VXT6, would you send me your shopping list?
Here is my list of caps, numbered according to the PCB. Height may be ±1mm, due to the black goop (which is neither brittle nor conductive).

Main board caps (all marked 105c)
#	V	uF	diam	height
1	25	330	8	12
2	63	100	8	15
3	63	47	8	15
4	50	12000	30	53
5	50	12000	30	53
7	25	1000	10	17
8	25	470	8	15
9	25	470	8	15
10	25	1000	10	17
51	50	10	5	10
201	50	100	8	12
202	50	100	8	12
204	25	100	6	10
301	50	100	8	13
302	50	100	8	13
304	35	47	5	13
502	50	10	5	13 nonpolar
505	50	10	5	13
613	50	100	8	12
CA7	63	470	13	22

Switch board caps (all marked 105c)
#	V	uF	diam	height
401	50	10	5	12
404	50	4.7	5	12
408	25	100	6	12
410	25	100	6	12

[Per Hansson]

Re: Recapping KRK VXT6 without original datasheets

Audio amplifiers don't usually use switchmode power supplies.
Instead they use a big (line frequency) transformers like here.
This means none of the caps usually are required to be low ESR.
So just selecting "general purpose" caps with a 105°C temperature rating from the Japanese manufacturers is enough.

Have you checked if you have any voltage on the big caps after replacing them?
It sounds like something might have gone bad (fuse?) based on your older post here:
https://www.badcaps.net/forum/showpo...5&postcount=10

[slerner]

Re: Recapping KRK VXT6 without original datasheets

Thank you for the quick & excellent response! It's a huge relief that I can use general purpose caps. And thanks for fixing my table.

The fuse idea is interesting. There was so much heat with the initial failure, that I did expect to find a fuse blown. There's nothing inside labeled 'fuse'. However, as Capsleaker mentioned in that other thread, R55 & R56 may serve as fuses. Those look intact on my original board. And on the new boards, of course.

But, [and I presume this is your point] I also found three yellow boxes wired between the mains and the transformer. Amidst the black goo I found cbb62b printed on one. When I searched that ID, I found that it's a metalized poly film capacitor. https://pdf1.alldatasheet.com/datash...CH/CBB62B.html And on the list of 'similar products' I noticed an automotive circuit breaker. Ah ha!

I powered up the unit and YES, my probe-style voltage detector beeped when it touched the main board's power plugs. So, it's good to know the transformer is still working.

I also used the multimeter to test for voltage across the leads of the caps I replaced - nothing. This perplexes me. But, it's the old board that's currently installed and the crash might have fried something else on it. Each time I swap boards I risk breaking something. So, I think I'll finish recapping at least one new board and install it. If the unit still doesn't work, the diagnosis at least ought to be simpler with a fresh board.

Thank you again for your kind advice!

[slerner]

Re: Recapping KRK VXT6 without original datasheets

Ok, one more question.
I've loaded my digikey cart with everything I need. All well-regarded brands Panasonic, CDE, Nichicon, Rubycon. A couple are Wurth, which I haven't heard anything about. But, since it's a German company I figured it's good. Also, some Kemet.
Q: I have already replaced the TWBOR 12000uF 50V 105c 30x50mm snap-ins with JCCON 63V. [I recall reading somewhere in the JCCON docs that these have a 52V "minimum operating voltage". Honestly, I've been unable to find that wording again and maybe I mis-read it. 52V-63V seems like a crazy spec.] I'd like to buy better quality. But, digikey only stocks a 12000uF ≤ 50V in 3000hrs/85c. see link below. To me, a 3000hr/85c Nichicon, Rubycon or CDE seems like a step up from the original 105c/?hr TWBOR or the 2000hr/105c JCCON. Should I go for the 85c?
https://www.digikey.com/en/products/...8Lmqh5JRMYjVAA

[slerner]

Re: Recapping KRK VXT6 without original datasheets

Have you checked if you have any voltage on the big caps after replacing them?
It sounds like something might have gone bad (fuse?) based on your older post here:
https://www.badcaps.net/forum/showpo...5&postcount=10

Umm… I thought I had checked the voltage, but I guess I had not. It turns out my Klein voltage detector pen gives a little beep whenever it touches anything. That's all I got when I touched the board's power leads. If I push the probe into a mains outlet it gives a much louder beep-beep-beep.
The reason I discovered this NOW, is I just installed my new-old-stock freshly recapped board and the amp still does nothing. No lights, sounds or heat. Honestly, I was worried that the unit failed so dramatically without blowing a fuse or circuit breaker. That seemed like a fire hazard. Instead, I guess the hazard was me. There seem to be circuit breakers on each of the 3 the mains wires into the transformer. Little yellow boxes buried in the black goop. I assume the next step would be replacing those?

[Per Hansson]

Re: Recapping KRK VXT6 without original datasheets

There seem to be circuit breakers on each of the 3 the mains wires into the transformer. Little yellow boxes buried in the black goop. I assume the next step would be replacing those?

Those are just EMI filter capacitors, they will be fine.
Your fuse is in the bottom of the IEC input socket:


P.S: The black gunk can be conductive, check out these EEVBlog videos of a similar KRK set:
EEVblog #1072 - KRK Rokit 6 Studio Monitor Speaker Repair
EEVblog #1073 - MORE KRK Rokit Black Gunk Speaker Repair

I'd like to buy better quality. But, digikey only stocks a 12000uF ≤ 50V in 3000hrs/85c. see link below. To me, a 3000hr/85c Nichicon, Rubycon or CDE seems like a step up from the original 105c/?hr TWBOR or the 2000hr/105c JCCON. Should I go for the 85c?

Yes, using 85°C rated caps for mains frequency is no problem at all.
I would 100% choose one of the Japanese 85°C capacitors over the other 105°C examples you provided as momaka said in your other thread here:
https://www.badcaps.net/forum/showthread.php?t=115310

[slerner]

Re: Recapping KRK VXT6 without original datasheets

HA! I can't believe I never noticed that! It's just like the picture. But, I can't figure out how to open that door. Wait - I just did. The fuse is burnt up. And there's a spare in the compartment. I swapped it out and IT'S ALIVE!! OMG I can not thank you enough!

[slerner]

Re: Recapping KRK VXT6 without original datasheets

Oh, I forgot to say. Yes, I saw the Rokit video. My model seems to have a different formulation. It's not brittle and I get no continuity through it. It's actually so gooey I ruined a good brush scrubbing it off my hands. The next day I found a better solution. There's a solvent pad called Remove. It's for cleaning off medical adhesive. That worked like a charm.