Tannoy Reveal 6D

[Khron]

Re: Tannoy Reveal 6D

Caps are best tested out-of-circuit, ie. removed from the board.

That C22 appears shorted due to the reason i've stated above

Re: finding caps - they're all pretty clearly marked on the top of the board.

C15 & 16 = the 8mm diameter ones, closest to the connector on the right: https://www.badcaps.net/forum/attach...1&d=1467844995
C22 & 23 = the 5mm(?) diameter ones, next to C15/16: https://www.badcaps.net/forum/attach...8&d=1467845455
C11 & 12 = the blue 5mm diameter ones, closest to the small black electrolytic, near the middle of the board: https://www.badcaps.net/forum/attach...1&d=1467844995

[Valden]

Re: Tannoy Reveal 6D

Yes, I'll have to remove any suspect caps from the board for testing.

While the schematic for the 6D is helpful I need to remember that I'm working on an 8D now. There are some differences, including with cap numbering. That schematic for the 8D would be really handy - which I will pursue, with Tannoy UK and the repair guys at my local audio store.

[Valden]

Re: Tannoy Reveal 6D

The component numbering with the 8D is indeed different from the 6D. The 6D schematic will be useful as a guide only.

I removed the capacitor I suspected was shorted, but testing off-board shows it's not. This is the capacitor that has its negative terminal connected directly to the outlet of the 7915. It's in the role of cap 12 in the 6D schematic. It certainly appears shorted when tested on the board. The same capacitor in my good monitor does not do this; it counts up like a good cap should. Something's fishy.

Khron, can you please explain how removing the 7915 and testing as described in post 117 will help? Your guidance was 'With the whole thing powered off, set your DMM to diode test ( -|>- ), put the black probe on a ground point (remember to pierce through the oxide layer on whatever solder joint you choose), and then with the red one, probe the output of where the 7915 was (or alternatively, if it's easier, on pin 11 of any of the 14-pin opamps)'. I can do this, but what are we looking for here? Are we looking for a problem on the filter board that is putting DC into the audio circuit, in part causing the woofer cone's extension?

Thanks.

[Th3_uN1Qu3]

Re: Tannoy Reveal 6D

Remove the 7915 then, it is almost guaranteed to be faulty.

[Valden]

Re: Tannoy Reveal 6D

Hello Unique.

Thanks for your encouragement. You might not have read in post 116 that I've already replaced the 7915 negative voltage regulator. It made no difference.

I'm hunting for causes of voltage drop in the negative half loop, possibly on the filter board. Insightful suggestions will be warmly welcomed.

Another piece of the puzzle:

- when I plug the speaker and front panel cables of the faulty monitor into the electrics of the good monitor, both the front panel light and switch work (as well as the speakers). The light does not work with the faulty monitor's electrics.

[Khron]

Re: Tannoy Reveal 6D

Either the 7915's faulty, or there's something shorted between the -15v rail and ground. My bet's on the latter

But that's why a measurement on the board, with the 7915 removed, would make things clearer.

With the 7915 removed, we could measure ONLY the resistance (or reverse voltage drop, with the multimeter in diode test mode) of the circuitry that's connected to the output of the 7915. Basically removing the 7915 as a suspect, or at least eliminating a variable / an unknown. You can then also test the 7915 out of circuit, to make sure whether it's good or shorted.

The "new" piece of the puzzle is nothing new - it just re-confirms that the problem is in the electronics of the "bad" monitor

With the diode-test-the-negative-rail thing, we would be determining whether there's something shorting the negative rail to ground or not. The lack of -15v on the filter board pushes its output towards the +15v rail, which in turn, causes the amplifiers to put out DC into the speakers.

Think of these dual-supply (positive & negative) circuits as keeping the speaker cone in balance, at idle. Each supply rail is pulling on the cone in opposite directions. If one of the rails is missing, the other rail has no opposing force countering it

[Valden]

Re: Tannoy Reveal 6D

Thanks Khron. Great explanation. I'll get that 7915 off so we can see what's up. Stand by.

[Valden]

Re: Tannoy Reveal 6D

Ok, I've got the 7915 off. Not easy. The heat sink mounting pin and the three legs of the 7915 are tricky to de-solder and move. The track that runs from the 7915's outlet hole to pin 2 of connector 1 was already damaged/lifted. To re-establish the connectivity that would have run through that outlet hole, to connect pin 2 of connector 1 to the negative terminal of what is cap 12 on the 6D schematic, I've soldered in a jumper wire between those locations. Are you happy with this? I believe they should be connected for the intended tests.

The diode test performed with the circuit inactive, with the black probe on the ground under the big caps and the red probe on pin 2 of connector 1 gives a reading of 656. I'll post again in a minute with voltage tests.

[Khron]

Re: Tannoy Reveal 6D

That doesn't sound like a short-circuit.

With the 7915 removed, there won't be much of a voltage reading to read

Am i mistaken, or had you at some point mentioned already replacing that 7915? Or were you just thinking about ordering a new one?

Given this fresh information, that would indeed point toward that 7915 being the actual problem. As mentioned before, 33v at its input would point to little or no current being drawn through the 220ohm 5w resistor "upstream" of it.

[Valden]

Re: Tannoy Reveal 6D

Voltage test results with 7915 removed and with DMM black probe on ground under big caps:

- with red probe on pin 2 of connector 1 (same as 7915 outlet hole), voltage is +3.8 V.

- with red probe on outlet pin of 7815, voltage is +15V.

I've used plus signs so you know I've read the meter correctly.

I'll look above to see if there were other tests you asked for.

[Valden]

Re: Tannoy Reveal 6D

I had already replaced the 7915. Doing so made no difference to voltage readings, but did make the woofer extend. A bit confusing, I'll admit. I checked for short circuits my work might have introduced but found none.

[Khron]

Re: Tannoy Reveal 6D

I assume / hope you had mounted the new one the correct way around, right?

Hmmmm...

I can't quite recall, had you measured the output of the regulators at any point, without the filter board connected?

[Valden]

Re: Tannoy Reveal 6D

I did measure the regulators with the filter board disconnected, this afternoon. IIRC, the 7915 was around 7V. I've just checked again, but this time with the 7915 removed.

- red probe at outlet of 7815 is 15V

- red probe at outlet hole of 7915 (measured at pin 2 of con 1, as above) is -14.5V. Ha! Makes me think we don't need no 7915!

[Valden]

Re: Tannoy Reveal 6D

Also, FWIW, with black probe on power board ground I checked resistance of the 14 pin opamps and the 8 pin IC on the filter board (circuit inactive). The only 0 ohm readings were each opamp pin 11 and pin 8 of the 8 pin IC. No apparent shorts there.

[Khron]

Re: Tannoy Reveal 6D

Resistance between where the 7915's output should be, and pin 11 (of 14) / pin 8 (of 8)?

Ok, those voltage readings are officially WEIRD...

Check the rectifier bridge as well, with the diode tester on your multimeter.

Also, double-check the traces between the rectifier bridge, the big fat caps (have you measured the voltage across each of those?), the 5w resistors and the voltage regulators.
I've seen / read about that brown glue corroding traces, in time. I wouldn't assume all traces are still in one piece, so i'd double-check everything i can.

[Valden]

Re: Tannoy Reveal 6D

Will do, in the morning. It's half past midnight here in Oz.

Thanks for your help.

[FeenixMusic]

Re: Tannoy Reveal 6D

Lots of knowledge on this thread! I have a pair of Tannoy 6d studio monitors and when I power them up there's an awful crackling noise. The volume knob has no effect and the crackle is present even when the monitors are not connected to any audio source. Does anyone have any idea what might cause this? Has anyone seen it before? In the meantime, with all of the mentions of this horrid brown glue I'm going to start by cleaning the circuit boards up. Thanks guys.

[Valden]

Re: Tannoy Reveal 6D

Lots of knowledge on this thread!

Yes there is, but not from me! I'm hardly the person to reply to your first post Feenix, but since I'm awake down here in Oz and the knowledgeable folk up topside of the planet are asleep - welcome.

See my next post for evidence of what a noob can try and even accomplish with help from gurus here, in attempting to fix these nice sounding but shitly made Tannoy Reveals.

[Valden]

Re: Tannoy Reveal 6D

Yay! I've got -15V from the L7915CV negative voltage regulator, along with +15V from the 7815 positive regulator. I'll try to post a pic taken with my iPhone showing how I've glued the 7915's heat sink to the back panel and used jumper wires to bypass the damaged tracks, caused by removing the 7915 and heat sink twice. I need a lesson on removing multi-pin components elegantly. 😳

I'll try plugging in stunt-double sacrificial speaker to see what happens.

[Valden]

Re: Tannoy Reveal 6D

Hmmm. Keep the cork in the champagne for the moment. I attached a little 8 ohm speaker and a second or so after switch on, it extends fully and stays there. Pop! It did it a couple of times so it wasn't cooked instantly.

Right'O. More probing for me. I'll run the tests you suggested yesterday Khron.