Tannoy Reveal 6D

[Mattstudio2]

Hi there,i have a pair of 6ds that seem to have done the same thing over a year ago... Sound appeared to become distorted from one box. Then the next day it was gone altogether.. I did however manage to get the schamatics out of tannoy..so was able to start tracing the fault. As there was now no warranty support for thia product i pulled the apart and by a process of elimination, think i've narrowed the fault down to the amplifier board... But hit a brick wall when the caps appeared to test okay...
I'll sit down with this thread,the schematic and the amp module and see if i can't find the problam...

[midibob]

I'm sure you'll get plenty of support from here if you get stuck.
I would start with gunk removal first and most importantly the stuff that's gone hard.

Good luck
Midibob

[midibob]

Shock, horror.

One of the tweeters has now gone open cct.
As these have only been used in the studio as monitors they've never been played loud so I'm a bit miffed.

At about £50 for a spare it's not worth replacing as the speakers didn't cost that. I'm hoping to have a go at repairing it as it could just be a fractured wire to the voice coil. Problem is I can't get the flipping thing apart.
Even under the microscope it's difficult to see how it separates.

Anyone had a go at one of these?

Midibob

[midibob]

Managed to get it apart in the end but the bad news is the voice coil was toast.

Midibob

[masterlink]

I recently experienced the same problem with one of my 6D monitors, out of the blue a loud pop then a constant hiss after switching it on and no sound thereafter. It's a real shame as they've been absolutely flawless since I bought them new nearly 8 years ago.

Midibob, your tips have been invaluable. So far i've managed to disassemble the amp and remove most of the dried brown glue from the PCB, though I've no electrical testing gear so i'm hedging my bets a bit that it's R18 that's faulty (I couldn't even see it on the board at first, it was hidden under so much glue!). I'm going to replace it and see what happens; if that's no good there's a local guy I know of who fixes up sound equipment.

Btw, I don't know if you've found one yet, but I came across this 120 Ohm 5W radial resistor from Farnell: http://uk.farnell.com/multicomp/mcpr...-5w/dp/1737463

PS: A tip for others for opening up the speaker - I eventually managed it by using a small flat-head screwdriver inserted between the corners of the metal back plate and the cabinet to gently prise them apart.

[midibob]

Hi,

Yep, I did see that one at Farnell. If you look closely you'll see that it's US stock only and it's £15.95 delivery charge to the UK!!

Hope you get yours sorted. You'd think there must be something that would shift that gunk without damaging anything else but I've never found anything. No substitute for a bit of elbow grease and a scraper

Good luck
Midibob.

[Khron666]

Well, on the other hand, you COULD try a "normal" axial 5W resistor, like

http://uk.farnell.com/multicomp/mckn...5ws/dp/1903932

and just bend one of the legs so it's parallel with the body Think of a J or (asymmetrical) U shape. If you wanna be really "pro" (or "paranoid"), you can slip some cable insulation on the bent leg, or some suitably small-diameter heatshrink.

And if that bent leg needs extending, a piece of wire or a thicker resistor/cap leg soldered on, can work wonders



Should be just fine, since "even" the originals seem to have been tacked / "hacked" on there with all that glue...

[masterlink]

Hi Midibob,
I went out and bought a multimeter today and did some testing around the board. It looks like it is R18 and L1 that have gone; both read open circuit. I've swapped out R18 for another 7K5 resistor, but obviously L1 is another matter. As Khron666 has pointed out above, would an axial resistor do in it's place (obviously ceramic still)? Did you use something similar for your repair given that you couldn't find the radial type?

[Khron666]

If it's rated for 5W, i don't see why it wouldn't work Of course, you might wanna tack it in place with some sort of heat-resistant adhesive.

A drop of RTV rubber, perhaps? I seem to remember silicone's slightly acidic when curing...

http://www.mitre10.co.nz/how_to_guid...icone_sealant/

Yep, the bathroom sort seems to be indeed acidic

[masterlink]

Thanks for the tips Khron, I'm a bit of a noob to electronics. I normally deal with stuff 'inside the box' (web developer by trade!)

My only concern with using a different type of resistor is how it would affect the audio, as I bought the monitors as a matched pair. Would it have any effect on the frequency response or sound character using wirewound over metal film?

[Khron666]

Nope, these resistors are on the power rails, just before the voltage regulators that drop the voltage from the "high" (whatever voltage the power amps are supplied at) down to the +/-15v needed for the small-signal stages (S/PDIF receiver, digital-to-analog converter, and the opamps that make up the crossover and so on).

Unless you're one of them "audiophool"-types, i *seriously* doubt you'll notice any non-auto-suggestion-induced differences But since you actually got studio monitors, that pretty much rules that out

Not to mention that such power resistors rarely (if ever) come in tolerances tighter than +/-5%, so... Potentially, you could have a ~10% difference between the resistors in the two monitors, straight out of the factory

[masterlink]

Haha, no I ain't no 'phooool I'd just read that wirewound types had less noise / more inductance but I guess if they're not in the signal path it's not going to matter. Good point about the tolerances too.

I'll get some on order and hopefully have the monitor fixed up soon. Thanks again!

[Khron666]

Glad to have been of assistance And yeah, i definitely like to "keep my feet on the ground" (ie. no "phoolery" here either )

[masterlink]

Well...good news and bad news. The good news is I replaced L1 with a similar type 120R 5W resistor I found on eBay, put everything back together and the monitor came back to life! The bad news... after about five minutes of listening the sound then faded out to nothing

While it was working, the sound of the repaired monitor was a few dB quieter than the good one. So I raised the trim pot to about half and all seemed well, played a few reference tracks, all good. I fiddled with the trim pot again after about 5 mins of listening and that was when the sound faded and wouldn't come back.

I've taken it apart again and tested the pot and that seems ok, gives readings of 4.8K at its lowest and 3.2K at its highest. So, i'm at a bit of a loss as to what to do next. Anyone have any ideas what it could be?

[midibob]

Could be a few things.

Don't forget the DIL switches as they can go intermittent. Just flicking them up and down a few times seems to clear them for a while. (At least a year in my case).

Otherwise you'll need to dig a bit deeper. Are the caps OK? This has already been well documented.

Make sure both the supply rails are still good.

Good luck
Midibob

[masterlink]

You know, it could well have been the switches. I reset them just before when i'd taken the monitor apart again. Now i've put it back together, all seems well! Equal levels coming from them both with the same settings

I've been listening for a good half hour now with no problems, I don't think i've ever enjoyed hearing them so much!

Thanks again, Bob!