Tannoy Reveal 6D

[Khron]

Re: Tannoy Reveal 6D

Well, as the old saying goes - even a kick in the a*s is a step forward

But yeah, with that 7915 issue out of the way, that indeed narrows down the possibilities considerably.

[Valden]

Re: Tannoy Reveal 6D

So... With the new 7915 in circuit (and wired up correctly? ), you ARE getting -15v at its output?

Yes, the relocated and custom wired 7915 is producing -15V at the output. Having that working correctly makes diagnosing the other fault, up on the filter board by the looks of it, easier!

[Khron]

Re: Tannoy Reveal 6D

Yes, sounds like the 8D has two of the LM3886 bridged, driving the woofer.

So... With the new 7915 in circuit (and wired up correctly? ), you ARE getting -15v at its output?

Well, if the finger-thermal-testing doesn't reveal anything relevant, the only other step i can think of is quite tedious, but should pretty much totally clarify things.

Black probe clipped / "permanently" connected to ground, and probe every leg of every opamp on the filter board. Note down the readings and post them here.

The outputs of the LM837 (quad opamp) are on pins 1, 7, 8 and 14, and the outputs of the LM833 (dual opamp) are pins 1 and 7.

https://cdn.badcaps-static.com/pdfs/...a12f80b5d7.pdf
https://cdn.badcaps-static.com/pdfs/...2cc9f50a3d.pdf

If both the woofer and tweeter are affected, and the -15v rail works as it should, i'd expect the issue to be "upstream" of the crossover stages, ie. before the high/low-pass filters for the tweeter/woofer.
Not sure if the filter board is the same between the 6D and the 8D, but on the posted schematic, that would be anywhere between the inputs and IC2B - you can see the green signal line splitting off to the right (entering a subsonic-high-pass-filter section) and upwards (entering the tweeter high-pass)

[Valden]

Re: Tannoy Reveal 6D

A quick test with that sacrificial stunt-double speaker shows that my voltmeter readings from my previous post play out as expected. The speaker cone sits still when hooked up to the tweeter pins. It pops out fully extended when connected to the woofer pins.

[Valden]

Re: Tannoy Reveal 6D

OK, this is interesting. I've checked voltage at the speaker connector pins. Red probe to positive speaker connector pin.

- with the good monitor, it's 0 for woofer and tweeter, with filter board connected.

- with the faulty monitor, its 14.9V for the woofer with the filter board connected. With filter board disconnected it's 0V.
- For the tweeter connector, it's -15V with filter board connected and -22.2V with the filter board disconnected.

Explain me that! Wait - I've found a problem with my temporary 7915 wiring. Because the power board was upside down when I was soldering I put a wire from the 7915 output to the high frequency audio connector pin. I've corrected this. The pic below shows the red wire has moved from pin 5 to pin 2, comparing with the pic in post 139. I'll now recheck those speaker connector voltages. Hopefully nothing's blown up.

New measurements are: tweeter pins are 0V with filter board connected and disconnected; woofer pins are 14V with filter board connected and 0V disconnected.

I'll go out on a limb and suggest it's a shorted low frequency opamp on the filter board, putting 15V into the low frequency audio track. I spoke with the tech at my audio gear supplier and he talked about the opamps being skittish in these monitors. He suggested I try to feel if one is a lot hotter than the others. BZZZZDT. Or look for smoke, of which I've seen none.

[Valden]

Re: Tannoy Reveal 6D

I've scraped goop off the even numbered pins of the three amp chips. I'm getting -37.1V at each pin 4, being the negative rail connection.

[Valden]

Re: Tannoy Reveal 6D

I proposed 'A shorted amp chip?' Probably not actually.

The amp chips' output is on pin 3. Pin 3 of the middle chip goes to one of the woofer connector pins. Pin 3 of the left chip goes to the other woofer connector pin. This suggests that the middle and left amp chips work in reverse phase. One pushes the cone while the other pulls.

Yep, from following the tracks, that is how the left amp chip works. While the audio input goes to the positive audio input pin 10 of the middle amp chip, it branches off and goes to the negative audio input pin 9 of the left amp chip.

Remember, this is for a Reveal 8D, which has three amp chips. The 6D has two.

[Valden]

Re: Tannoy Reveal 6D

The HF output is extending the test speaker too. The problem is affecting all the amplifiers.

The amplifiers run off the +/- 36V rails, not the regulated +/- 15V rails. Will look for a problem in the 36V rails.

- I'm getting 36.7V and -36.7V from the rectifier.

- looking at the LM3886 amplifier ICs, all three have 36.3V at supply pins 1 and 5 and 16V at audio output pin 3, except for the amp chip closest to speaker connectors, which has 0V at pin 3. A shorted amp chip?

[Valden]

Re: Tannoy Reveal 6D

Khron asked 'Resistance between where the 7915's output should be, and pin 11 (of 14) / pin 8 (correction - pin 4 is ground) (of 8)? Answer - 976 ohm for all them. The 8 pin IC is labelled JR448AC LM833N. Another opamp? Google might know.

Edit - these measurement were taken with the 7915 back in circuit and apparently working.

The current challenge is, what's making the woofer cone extend outwards? This could be because the negative voltage rail is not reaching one of the amplifier chips. I'll try the stunt-double speaker with the HF output.

[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.

[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

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.

[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

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

Thanks for your help.

[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

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.

[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!

[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 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.

[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.