Tannoy Reveal 6D

[Valden]

Re: Tannoy Reveal 6D

Yes, my initial findings this afternoon led me to be concerned about the 7915. It is looking rather guilty. I'll compare results against my good 8D tomorrow to confirm.

My multimeter is a pretty shitty generic POC, dressed in Dick Smith Electronics labelling. It does measure negative voltages, though I sometimes forget to make note of them. I'm sizing up a Fluke 179 or 3000 FC, to make life more enjoyable.

[Khron]

Re: Tannoy Reveal 6D

What voltmeter / multimeter do you have?

Most digital multimeters (DMM's) WILL put a "-" sign in front of the reading, if the black probe is, say, connected to the ground of the circuit, and the red one to a negative voltage

Also, the pinouts of the 7815 and 7915 are NOT mirrored.


versus


Probing between the output of the 7815 and the 7915 should've produced a reading around 30v, actually: 15v - (-15v) = 15 + 15 = 30v (difference between the two points).

So i guess you have your culprit right there - the 7915 regulator's... not really regulating much anymore
Either that, or there's something fishy between the 220ohm 5w resistor, and the 7915's input pin.

A reading of 17.6v between the 7815 output (which should be +15v relative to ground) and the 7915's input would mean that the latter is around -2.6v relative to ground, when normally that should be in the -18v area.

[Valden]

Re: Tannoy Reveal 6D

Thanks for these suggested checks. I will pursue them in the morning.

Given my concern that power supply to the filter board might not be good I've been testing the 15V regulators. My findings so far are:

- the L7815CV positive voltage regulator is delivering 15V, measured from outlet to ground. Looks good. This one was easy to measure.

- the L7915CV, being a negative voltage regulator, was tricky to measure. In the end (and after consulting the schematic for the 6D and comparing the 8D's board truth - similar in this respect) I probed from the outlet of 7815 to the 'outlet' of 7915, then to the 'inlet' of 7915. The results were 15V and 17.6V respectively. I think this means that the 7915 is working, and is chewing up a couple of volts in doing that work.

- Not being an expert, I was curious about results from probing the 7915 directly. Sure, the inlet and ground pins are reversed relative to the 7815. Apart from that, I found that measuring from outlet or inlet to ground would not produce 15V, but only 0 or about 2.5V. My son and I think this is correct and is due to this regulator being situated in the negative half of the 15V loop.

Thoughts?

More testing tomorrow.

[Khron]

Re: Tannoy Reveal 6D

See if you can use a crocodile / alligator clip to hook the black multimeter probe to a ground point (solder a piece of wire to one of the ground legs of the two big filter caps, if needed), and then probe around for voltages "down the line", with the red probe.

I guess you can follow the 6D schematic - apart from maybe a 2nd amp chip for the woofer, i doubt the circuitry's much different.

Right on the rectifier bridge (and, i assume, on the main filter caps) the voltages look normal. Check the voltages on each leg of the two 5w resistors, then on the input & output pins of the 7815 & 7915 regulators (datasheets are easy to find).

Then move on to the connector going to the filter board. Measuring on the underside of each end (on the amp board & filter board) would be the most certain, and remember to try to pierce the oxide layer.

Also, check the voltages on the connector going to the front panel - there should be a +15v and a-15v going to that as well.

I assume they "went to town" with the crap brown glue in your speakers as well? If that's the case, copper trace corrosion is (also) very likely.

Re: the 9.2 ohm measurement - oxidation and other crap on the outside of the solder joints or connectors can easily account for that That's what we have those sharp tips on probes for

[Valden]

Re: Tannoy Reveal 6D

Tannoy Reveal 8D symptoms continued:

- correction to the measurement of the voltage being passed from the power board to the filter board. I measured the wrong pins. TBA.

[Valden]

Re: Tannoy Reveal 6D

Tannoy Reveal 8D symptoms continued:

- using an audio probe reveals that the audio signal is not getting off the filter board. I'm picking the audio up on the board near the input jack and then at some components nearby, but not further across the board towards the connector that takes it to the power board. Will check the digital/analog input switch.

[Valden]

Re: Tannoy Reveal 6D

Ah, the white ceramic resistors. I know those ones well. In one of the pics in a post of mine above you'll see I've floated the 120 ohm one away from the board. As experienced by TJC on page three, it was cooking the board.

In the 8D, it's a 5W 100 ohm ceramic resistor rather than 120 ohm. I've measured it in situ and I'm getting 100 ohms. So it looks OK. I'll continue checking other components. Any suggestions welcomed.

In trying to identify what's causing this loud hum, a fresh summary of symptoms is:

- digital board is not working
- shortly after switch on, a loud hum/grinding buzz noise comes from the speakers, irrespective of digital/analog input selection
- front light is not working but mute function is working. It stops the loud hum.
- transformer seems to be OK, delivering 27.1V each side, which is the same as the transformer in my good 8D.
- the rectifier is measuring as 54.4V AC at the two inside AC pins and 73.8V DC on the two outer DC pins.
- the two white ceramic 5W resistors seem OK, measuring as labelled; 100 ohm and 220 ohm.

I'll report further findings. Suggestions welcomed.

- OK, I just plugged the woofer from the broken 8D into the power board of the good 8D. The woofer works perfectly. I do wonder why I was getting 9.2 ohm measured through the woofer's connector, but won't be dwelling on that.

- power supply to the upper filter board looks Ok. I'm getting 15.4V between pins 1 & 2 of connector 1 on the power board, which links up to the filter board.

- thermal fuse adjacent to amp chips is OK

[Khron]

Re: Tannoy Reveal 6D

It's one of the two big white 5W ceramic resistors, on the bottom of the "power board".

As you might've read in this thread, it's really common for those to fail open.
On the previous page (page 5) you can see i up-rated them to 10W ones, "just in case". I kept them at the same values (120ohm for the positive rail and 220ohm for the negative one).

[Valden]

Re: Tannoy Reveal 6D

Ah ha! The front LED has indeed crapped out, I noticed last night. I will go looking for that dropper resistor. I realise we're talking about an 8D here, but from the schematic for the 6D (which I have from this thread - at post 28), can you name it or pinpoint it please? Thanks.

[Khron]

Re: Tannoy Reveal 6D

That's kinda what i figured - the only real way the digital board could cause noise is if it was selected with the switch on the back.

Other than that, perhaps if the dropper resistor on the positive rail crapped out (ie. went high-resistance or open-circuit) - although that might "kill" (ie. turn off) the front indicator led as well...

Well, in that case, my prime suspect would be the speaker connectors

[Valden]

Re: Tannoy Reveal 6D

Sorry, I should have been clearer. The loud hum/buzz noise a couple of seconds after switch on happened at first with the faulty digital board uninstalled, then again with that board installed. So it appears to be independent of the digital board.

I will go ahead and swap the woofer over to the good monitor tomorrow and test it. Hopefully it's OK, though the 9.2 ohm reading has me wondering. I guess the fact it was producing the buzzing noise is a positive sign.

Thanks for your help so far.

[Khron]

Re: Tannoy Reveal 6D

And you're positive those issues stem from the digital board?

The speaker connectors in (at least) one of my Precision 6D's had gone wonky, and upon closer inspection, one of the "tongues" inside the connector going to (i believe) the woofer just fell out - i ended up just stripping & soldering the wires to the bottom of the board.

No, swapping connections shouldn't be an issue. If a voice coil goes open-circuit, you'll "just" not hear sound out of that particular driver.
In fact, that's a basic troubleshooting step

[Valden]

Re: Tannoy Reveal 6D

Hi Khron.

Yes, the digital board in one of my 8Ds has been out of commission for a couple of years. I fired the monitor up this afternoon and got a loud buzz, so switched off quickly. Probing so far reveals nothing unusual except that resistance through the speaker connectors is inconsistent. 4 ohms for the tweeter, but 9.2 ohms for the driver. I would having thought that should be 4 ohms as well. I'll swap that speaker to the good monitor and test it. Any risk to the circuit in the good monitor in running this test?

Thanks.

[Khron]

Re: Tannoy Reveal 6D

As far as i recall, it's no real big deal.

3.3v regulator, an opamp (or two?), S/PDIF transceiver and the DAC.

Is it giving you trouble as well?

[Valden]

Re: Tannoy Reveal 6D

Hi folks.

Does anyone have the schematic for the digital board in these Tannoy Reveal 6D and 8D studio monitors? As mentioned above, I found the schematics for the power board and the pre-amp/filter board, at post 28 of this thread. Excellent.

I'll keep looking in the meantime.

Regards.

[Valden]

Re: Tannoy Reveal 6D

As mentioned above, my son and I have repaired our Tannoy Reveal 6D studio monitors. The job became easier once we found the schematics linked above in this thread. Thanks for those!

Background: In 2008 I purchased a pair of Tannoy Reveal 6Ds for mixing/mastering in our home studio and a pair of Tannoy Reveal 8Ds for listening to the results in our family room. Both pairs have had faults. A few years ago I pulled a working digital card out of one of the 8Ds and installed it into one of the 6Ds (they're the same), to keep that pair working. At the moment the other 8D has a fault in the analog signal path - I'll get to that one day.

The latest problem with the 6Ds was almost complete loss of main driver output in one of the monitors. Actions taken in attempting repair were:

- swapping main drivers between the two 6Ds to check performance. The driver was OK. Pulling the drivers out of the cabinets is tricky. I used a heavy duty paperclip with a right angle tip about 3mm long, with a chisel point made with a Dremel, to insert behind the speaker surround inside each screw hole, to gradually ease the driver out. The rear surface of the driver's magnet housing is goop-glued to a cross brace inside the cabinet. It doesn't just fall out. Prising with a screwdriver would damage the front surface of the cabinet and the plastic speaker surround, so progressively pulling with the bent wire was safe and eventually worked. No damage done.

- Inside we eventually found that the white 120 ohm resistor on the power board had cracked solder joints. Wiggling it lifted a track from the board; a result of heat damage. We reinstalled the resistor using 15mm lengths of paperclip to move it away from the board. Unfortunately this first repair did not make the music come back.

- Next we found what looked like corrosion under the chassis ground screw, with the lead coming from the analog input connector. In trying to disassemble that we found that it had no effect. The screw ended up stripped, so we made a new ground connection, seen in the pics.

- My son and I watched this video by Billm and made the probe pictured below with an old guitar cable. With this and my son's old Roland amp we hunted around and discovered that while the low frequency audio was making it off the filter board to pin 3 on connector 1 of the power board, it was significantly attenuated at input pin 10 of the low frequency amplifier chip, with very low output at pin 3 of the chip. We checked resistor 9, the only component between the two points and it was OK at 510 ohms. By holding the board in the sunlight every which way and looking closely at the track coming from pin 3 we saw that it was corroded, probably from the goop applied to stop the connector from moving. We tried a quick jumper cable and the tunes came back! The jumper cable is now properly soldered in place, between pin 3 of connector 1 and the soldered junction of resistors 9 and 13. I'm listening to the Eagles greatest hits now - us dudes born in the sixties are allowed to do that.

Thank you to TJC on this thread for his Reveal 6D repair site we found before this thread, and his link there to the amplifier chip data.

Now let's see if I can post some pics.

Here's the audio probe. We played a familiar song into the analog input and traced high and low frequencies on the filter board. The highs go to pin 5 of connector 4 on the filter board. The lows go to pin 3.



The next two pics show the jumper cable that replaces the dodgy track from pin 3 of connector 1 on the power board to the junction of resistors 9 and 13.





Here's the fix to the 120 ohm resistor.



Here's the re-routed ground from the analog input jack.

[Valden]

Re: Tannoy Reveal 6D

Hello all. I've just joined, to say thanks for the posts, pics and the schematics and to share the repair my son and I have completed with our Tannoy Reveal 6D studio monitors. I have pics to post, which will be in the next post. Please stand by. :-)

[midibob]

Re: Tannoy Reveal 6D

My pleasure. It's nice to know it's helped folks.

[Khron]

Re: Tannoy Reveal 6D

UPDATE: Happy to say the Precisions work as well as could be hoped Considering i won't be gunning them 24/7, i quite hope the LM3886's won't mind the heatsinks being horizontal, though...

They at least "feel" like they reach lower down in the bass than my Soundcraft Spirit Absolute 4P's, with a wee bit more "sparkle" up top, and less midrange (~4KHz) shouty-ness / harshness.

Thanks a whole bunch for this thread, midibob

[Khron]

Re: Tannoy Reveal 6D

On the other hand, without this forum / thread, i might not have been so confident in grabbing this pair. Although i probably would've snapped them up anyway, but this gave me the extra confidence in a near-certain success