Tannoy Reveal 6D

[Khron]

Re: Tannoy Reveal 6D

Either way, congrats on the revival

[Valden]

Re: Tannoy Reveal 6D

Ah, Variable Resistor! hehe.

Thanks.

[Khron]

Re: Tannoy Reveal 6D

Variable Resistor 1

Well, sometimes you get lucky :P

[Valden]

Re: Tannoy Reveal 6D

It's not a voltage regulator? When I look at the schematic it's called VR1. And yes, it's rated at 1K (with no units, but Ohms it is! ). I'm happy to call it a trim pot, since that's what it's supposed to do.

Thanks for the advice on trying the contact adhesive. I have a can of CRC CO Contact Cleaner for such purposes. Expensive stuff! I've seen others using isopropyl alcohol.

I have to say, if I'd known that the main problem with this monitor would end up being the second surface mount component I lifted, I'd have been lifting them a lot earlier. Still, those days worth of looking at the boards and schematics and using my full powers of ESP paid off. It's surprising what can be achieved with the worlds crappiest multimeter. Sometimes when it's on the voltage setting it behaves more like a random number generator. Re those Brymen's, TME in Poland seems to be about the best source.

I have half a dozen supposedly failed negative voltage regulators on the desk, all of which test just fine. Oh well, spare parts.

[Khron]

Re: Tannoy Reveal 6D

Those aren't voltage regulator trimpots - they're just literally a volume control, for the tweeter channel

At least before bothering to source a replacement, sure, contact-cleaner's well worth a shot. Definitely can't hurt, anyway

Since they're trimpots, they're (obviously?) supposed to be continually-adjustable (as opposed to a multi-position switch). The schematic says that's a 1kohm trimpot, but you'd need (in an ideal case) to find one with a compatible footprint (ie. pin spacing, etc).

Then again, now that i read your message more carefully, they wouldn't necessarily need to be set to the same position, in both monitors. Mechanical things (ie. speakers) can easily have wider tolerances than electronics, so those levels should best be set using the actual tweeters, imho
Otherwise, even if you have the trimpots set the same, you're at the mercy of whatever sensitivity differences (dB per watt) the two tweeters might have...

[Valden]

Re: Tannoy Reveal 6D

Re the attenuated tweeter level, I had a look at signal strength at the voltage regulator on the filter board (the trim pot Khron mentioned) and compared the two monitors using the audio probe. The output from pin 14 of opamp 3 goes to pin 1 of the trim pot. With the good monitor the factory set output from the trim pot (pin 2) was a touch lower in volume than the input, to my ear. The trim pot appears to be adjusted fully clockwise, which appears to be fully attenuated, from fiddling with the one on the faulty monitor's filter board.

With the faulty monitor, the factory set position was also fully clockwise, but there was a big reduction in signal strength across the trim pot's pins. I found that in turning the fiddly adjustment screw through its 180 degree range, fully anticlockwise, that the output level came up, to equal the input, by ear. The trim pot is very intermittent during adjustment and has only two settings: fully loud at hard left and what sounds much the same in the middle.

Are these voltage regulator trim pots meant to be progressively adjustable, or do they have two or three settings? Would a drop of contact cleaner and some sweeping back and forth help?

FWIW I checked voltage levels with my POC meter (ain't got that Fluke or Gossen yet). The good monitor was steady at 3.8mV in and 1.2mV out, with an audible reduction in level from using the probe. This was measuring DC millivolts though. Wrong? Each time I checked the faulty monitor I saw readings of around 14 millivolts at pins 1 & 2. Que?? The opamps in both monitors appear to be working the same.

The outcome is that I'm now getting pretty good and reasonably balanced sound from the two monitors. The 'faulty' one might be a touch overdone in the high frequencies, but I'm not too fussed given where it's come from. I'll look into replacing that trim pot. I'll report on any markings I can find. Do we know the manufacturer and part number? I'm guessing a properly specced generic replacement would work?

[Th3_uN1Qu3]

Re: Tannoy Reveal 6D

Now would be the time to install a signal generator app on that iphone and trace thru the signal path for the tweeter amp. I am sure Khron can help you with this more than i can, as i have never taken apart this model monitor.

[Khron]

Re: Tannoy Reveal 6D

No worries, it's just "giving back to the community", as far as i'm concerned

Keeping information like this secret benefits noone, not even me

Attenuated tweeter, you say? In a pinch, you could fiddle with the trimpot that's on the output of the tweeter filter section (that's what it's there for, actually - fine-tuning the signal level at the input of the tweeter amp).

[Valden]

Re: Tannoy Reveal 6D

Before I forget, Khron, thanks for your patience and assistance with this. It's been very good of you, to respond so helpfully to a new member's problem. I've really appreciated your advice and encouragement.

[Valden]

Re: Tannoy Reveal 6D

I rang Jaycar and to my surprise they said they had just the thing. But when I got there, just before closing, and showed the girl the surface mount cap I needed, she said. 'Oh, I don't think we have any of those!' I settled for the next best thing - a ceramic cap of 10nF and 50V rating.

The monitor is working! But, the high frequencies are significantly attenuated. Could it be the ring-in cap I'm using? I'll check the schematic to see if opamp 2 (IC2) has anything to do with the highs. The tweeter itself is fine. The highs problem moves with the repaired electrics; the tweeter works with the good monitor's electrics.

[Khron]

Re: Tannoy Reveal 6D

There ya go then! Glad to hear you nailed it that quickly

You'll want the replacement to be rated for at least 25v though.

[Valden]

Re: Tannoy Reveal 6D

I decided to focus on the surface mount components that were single points of failure in terms of creating a short between the negative rail and ground. I lifted one end of C18. Nope. The short's still there. What about C21? Holy crap! The short's gone. Connect it again with a molten strand of solder. The short is back. Break the strand? The short's gone again.

With a bit of luck this could be the fix. Now I'm on the scrounge for a 10nF SM ceramic capacitor.

[Khron]

Re: Tannoy Reveal 6D

That's the only realistic way to hunt down short-circuits - separating the potential culprits.

Fingers crossed

[Valden]

Re: Tannoy Reveal 6D

Thanks for the suggestion re cutting the tracks. I'll have to start calling it the Frankenfilter board.

The short/s I'm hunting for is/are present when the board is unpowered, as well as powered. Bewdy!

*************

I've been checking out the Brymen BM869S. There's a very interesting test video on YouTube, by Joe Smith.

https://youtu.be/K-4L2JarVxA

[Khron]

Re: Tannoy Reveal 6D

There needn't be a "hard" or permanent short from the negative rail to ground inside one of the opamps - it might just be a transistor inside that is made to conduct fully when the opamp in question is powered.

A simpler test - get a nice sharp box-cutter knife / stanley-knife / whatever it's called "down under"
And then just (carefully but firmly) slice through the trace going to the negative supply pin of each opamp, one by one, and power-test the board between each operation.

Once you've detemined which one's the culprit, you can then just scrape off the solder-resist from both sides of the unnecessary cuts and bridge them with a solder blob (or a piece of resistor leg / wire, if needed).

I'd start from the opposite end of where the connector is, and work your way towards it. Once the semiconductors are cleared, then we can start suspecting the passives.

That being said though, you miiiiight wanna check the negative rail bypass caps (10nF between ground and -15v), if they're surface-mount ceramics - they've been known to fail shorted (i've revived several laptops that way )

[Valden]

Re: Tannoy Reveal 6D 8D repair

Status update for repair of Tannoy Reveal 8D studio monitor.

I have confirmed that the power board is working, by using a dummy load to simulate the filter board being connected. In this configuration the two voltage regulators are supplying +15 and -15V, as they should. However, once the filter board is connected, voltage at the output of the negative voltage regulator drops from what should be -15V to -0.1V, relative to ground measured under the big caps on the power board. Measurements taken at the connector of the dismounted filter board show that there is a short circuit between pins 2 and 4, being the -15V rail and ground. I'm presently hunting for that short circuit.

Using the filter board schematic for the 6D as a guide, the first suspect was capacitor 49, one of the two electrolytics on the board. With it removed from the board the short circuit persists. Thoughts then turn to the five LM837 quad opamps and the one LM833 dual opamp. The negative rail connects at pin 11 for the 837s and at pin 4 for the 833. However, resistance testing reveals no short circuit between pin 11 (or 4 for the 833) and any other pin on these ICs. Even if there was, none of these IC pins connect directly to ground. At least one other component would need to be shorted for a short in an IC to be part of the overall short circuit between the negative rail and ground. The suspect components are surface mount capacitors and resistors. Are these prone to failing and going open? If it's more obvious than this, I haven't seen it yet

So, I'm continuing to look for the cause of the short circuit between the negative rail and ground on the filter board. I'll have to start lifting the surface mount components one by one …

Don't call the priest for this board just yet.

[Khron]

Re: Tannoy Reveal 6D

A noble intention, but perhaps a bit premature / hasty

As i said - first i'd want to check / establish how things look from a DC perspective (voltages, operating points at idle etc). Once that's cleared up & settled, THEN it's time to move to check the AC behaviour.

Perhaps a bit late, but here's a "testing checklist" that might come in handy:
http://sound.whsites.net/troubleshooting.htm#test2

Although it must be said that some of the details there refer to an amplifier made up of discrete components, but the same principles apply
Also, see lower (section 11.0) for tips regarding testing the filter board.

[Valden]

Re: Tannoy Reveal 6D

I played audio so I could trace the signal through the opamps, to find if any are not working. Seems a reasonable approach. Luckily, the 7915s are only $1.85. But, the electronics store up the road has only 13 of them. Might not be enough.

[Khron]

Re: Tannoy Reveal 6D

Yeah, can't really imagine why you'd wanna do that

I mean, at least in theory, first you'd wanna get the whole thing to work ok in static conditions...

Now that i'm looking more at the filter schematic, it seems like the whole thing is DC-coupled, apart from the high-pass sections.
So at least in theory, if some sort of too-large signal(?) somehow messed up (some of) the input opamp stages, that might've blown/shorted something inside IC1.

But until you re-replace the 7915 and measure all the pins of all the opamps, i'm only speculating

[Valden]

Re: Tannoy Reveal 6D

Bugger. The Eagles killed the 7915 regulator!

I played my iPhone into the analog audio input on the filter board and the 7915 is now reading -0.5V at the output, just as it was before. Now it might not have been the audio that caused this, but that's the only thing I did. I'll buy a few more 7915s tomorrow and try to identify what's wrong on the filter board before playing audio into it. Sheesh!