Tannoy Precision 8D active studio speaker dead...

[wraper]

Check marked places.

[LektroiD]

Well spotted!

I have rerouted the trace and we now have power, proper input and output voltages at the regulator, expected voltages at the header, and the power LED on the front of the speaker is now operational once again.

However, no sound... I'm going to check out all of those opamps on the filter board next (unless there are other suggestions)...

[wraper]

Well, one of my first suggestions about LM3886:

Also measure voltage on the pin 8 (mute). I'm asking this because if the controller mutes the power amp, you wont get any sound even if amplifier is completely ok.

[LektroiD]

Mute pin ( is just bouncing around a few .mV. Same response on all of them

Pin 4 and 7 both go to ground.

[wraper]

Are you sure that pin 4 goes to GND? It is negative supply and should not be connected to GND. Even in single supply connection it cannot be connected to pin 7 in principle. Also I see thick negative supply trace on the top side of the PCB going behind LM3886's along the edge of the PCB.

As of considering normal dual supply connection (but check first pin 4, there must be -35V, must measure continuity to ceramic resistor on 7915 input):
Voltage on mute pin must go below zero to approximately -2.6V according to how I understand datasheet (it is current, not voltage driven). If current is not sinked, voltage will stay at zero and mute is on. I suppose all those pins are connected to one point, likely through resistors and further go to connector. Check where traces go and parts connected there.

[LektroiD]

Just tested with the front soft power switch connected and activated, there is -1V going into mute, and pin 4 was only earthed while there was no power, it is in fact, -36.6VDC

[wraper]

Just tested with the front soft power switch connected and activated, there is -1V going into mute, and pin 4 was only earthed while there was no power, it is in fact, -36.6VDC

That means it was not earthed, you just made wrong measurements somehow. I guess LM3886s should be working then. I would try to put some audio signal directly to power amp pcb. Maybe just touch audio input with tweezers or small screwdriver while touching metal part of it and listen if the hum appears in the speakers. Just be very careful to not short something, or some part may explode. I'm going to business trip today, so my further help might be delayed if any.

[LektroiD]

It's not easy to do any tests while the speakers are connected, the extra short cables are fixed into the cabinet (I don't want to tug at them too much as I know how flimsy these things are). The back needs to be virtually closed before I can attach the cables. This is one of the worst designs I've seen when it comes to maintenance, not to mention all the snot the boards are covered in. Considering these were £1000 each when new, I certainly won't be considering Tannoy when I next upgrade the studio.

Hopefully this pic will give an indication of the constraints I'm working within...

[wraper]

I see you have oscilloscope. Connect it instead of speakers.

[wraper]

Or you can check with oscilloscope if signal is present on power amp input instead. If not, check preamp.

[LektroiD]

Good call... I'll feed in a 1Khz square from my FG, see how far into the circuit it goes.

[LektroiD]

Fed a 1KHz square in at +/-1V, I got a sine out of one of the chip amps (pin 3 - output), the others displayed nothing. Then, due to the tight space I'm working in, I managed to short out two of the pins on one of the other chip amps, nearly welding the probe to it.

Now the sine I'm getting is modulated with another lower frequency sine, this added carrier sine is present on nearly all the connections of the chip amps.

[Yago]

Is the lower freq 50Hz?
Could have knackered a diode or cap in the PSU section and AC is getting through.

[LektroiD]

Back after waiting for some new test probes to be delivered. I seem to have misplaced my Tektronix probe adaptors which are safer for probing chip pins - those standard hook things are too clumsy for chip pins. Anyway...

I seem to be getting a waveform back into the power board, but I'm getting strange results from the chip amps...

There is a waveform going into two of the chip amps, but the output is flatline (zero/zilch/nada).

Mute pin has -1.06VDC going to it

I hope the sketchy illustration clarifies what's going on.

[Yago]

Saw this and thought of you Lektoid! :
http://www.ebay.co.uk/itm/Tannoy-Precision-8D-Amplifiying-Unit-tested-and-working-/191411958647?pt=DE_MusikInstr_Lautsprecher_Monitore&hash=item2c910ab377

Might be handy for the future to have a spare!

[LektroiD]

Saw this and thought of you Lektoid! :
http://www.ebay.co.uk/itm/Tannoy-Precision-8D-Amplifiying-Unit-tested-and-working-/191411958647?pt=DE_MusikInstr_Lautsprecher_Monitore&hash=item2c910ab377

Might be handy for the future to have a spare!

It would be perfect, except shipping only in Germany. 

[krivx]

I would contact and ask about shipping. Most sellers will, especially if you have good feedback already.

[LektroiD]

I asked about shipping, and he got back to me saying it would be somewhere around €20 depending which courrier, I asked if he could give me the exact shipping cost so I could buy it and not had a reply.

I would rather get the unit I have up and running to be honest, this evilBay thing is like chasing my own tail.

Anyone got any suggestions regarding the tests I did today?

[LektroiD]

may i suggest, since you did find a PCB track problem. would it be good to first completely eliminate the rest of the "spots" so that then you can maybe repair all the possible broken PCB as round 1? in a 25 yr old stereo drawmer compressor, i had to isolate channel 1 from channel 2 in order to find and repair all the PCB track related problems, maybe similar problem in this PCB too. so did that gunk actually corrode the track around the regulator? or it was something else?

Looks like I ripped the trace up when I swapped out the regulators. That's fixed now and I haven't noticed any other problems on the PCB

[LektroiD]

R23? I just checked for continuity, and yes it's tied to ground

[LektroiD]

did you managed to fix the amp? just curious ...

I battled long and hard, but eventually caved in and went for the evilBay option. Now the other speaker seems to have a slight issue making intermittent noises (without audio input), probably one of the crap caps drying out. I'll have a look when I can next muster the strength to get it off the stand (they seem to weigh about 15 tonnes, and I can't lift too much after a car accident last year).

Anyway, here they are in all their glory...

[pinyoro]

Beautiful studio!!

[LektroiD]

dang man .... if i were you ... i would try to get my hands on a meyer HD1 (or something similar analog sounding, silk tweeter etc) ... your gear seems to have so much analog sound in it ... you definitely need a better pair than those imo

btw ... that akai sampler with the floppy ... does it still work?

I use the analogue inputs on the speakers, not the digital.

After nearly 25 years working as a studio engineer, I found the dual concentric design much easier to find the sweet spot than separate tweeter/driver combination, which is why I have favoured Tannoy for many years. Up until the 8D's were working I was using my System 800 passives (which are now on back on my hifi separates next door). Once you have tuned your ears to a particular brand, it's absurd to move to another; just to spend the next 6 months tuning your ears to them. In many cases, speaker placement and room mode tuning is much more important than the speaker itself. Therefore, money is much better spent treating the room acoustics once you have found your weapon of choice. If the Meyers work for your ears then that's great, but I have no plans to jump ship any time soon.

Yes the sampler is fully working, also has USB card, which apparently is quite rare... However, I was thinking of selling the sampler as I don't use it much.

[LektroiD]

I have a problem with the replacement unit. This is an intermittent fault so may be why it wasn't picked up when it was sold.

Occasionally (usually after it has had No audio fed into it for a while), it drops by a few decibels, the only way to kickstart it is to send a few short bursts of high volume audio to it. Then it works normally, but this is not ideal as I have neighbours who I'm sure don't appreciate bursts of high volume audio emanating from my property.

I have tried the amp in both units to ensure it is not a faulty driver or cable.

I'm suspecting a dead opamp, but I don't want to look into repairing just yet as I'm in discussion with the seller to try to resolve this, and the unit may need to be returned in the same condition as it arrived. I just want some ideas as to whether this may easily be repaired, and whether to ask for a part refund on that basis. Provided it can be repaired.

[KhronX]

On these models (actually, both Reveal and Precision 6D/8D's), the most common issue is one or both of the 5W ceramic dropper resistors ahead of the voltage regulators failing open-circuit.

The brown glue drying out and turning corrosive and conductive is a ticking time-bomb, and the switches can go wonky too.

Most recently, the 80Hz high-pass switch on one of my Precision 6D's had kicked the bucket, after i took the back off to take care of an intermittent contact on the tweeter output connector.
Nothing a squirt of contact-cleaner and 20-30 operations couldn't fix

You can find the schematics here:
http://91.121.194.115/tannoyschematics.zip

The filter board is almost definitely the same. The only (electronic) difference between the 6D and the 8D is that the 8D has two bridged LM3886's driving the woofer, where the 6D only has a single one.

I hope this doesn't violate any forum rules, but there's a considerable-ish thread on this subject over on the badcaps.net forums:
http://www.badcaps.net/forum/showthread.php?t=16644