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Wednesday, 15 November 2017

Tannoy SFX5.1 Powered subwoofer repair.

Paul popped by.

"I've got this Tannoy subwoofer, it crackles and pops. Can you take a look?"

Yeah - why not......


It's a smallish cube, mounted on little cones, with a downward facing speaker...

I powered it up, and all was quiet. 

Just as I was about to connect the signal generator, I heard thunder in the distance .... and it got louder and louder! The speaker was popping and crackling alright. I quickly powered down.

I removed the screws around the outside of the rear panel, to reveal the speaker. The electronics and amplifier are mounted on the rear panel itself....

The main amplifier, a TDA7293 is heatsinked to the rear panel.










Removal of the board showed signs of distress....

Q151 and Q152 and there associated components had been running rather warm! The colour of the cases of the transistor should be black, you can see in the photo that they've changed to a sort of powdery brown.

Q151 is a 2SC1815, NPN, and Q152 is it's complementary PNP, a 2SC1015.











Static testing on the transistor tester showed both to be fine. But the fault seemed to exist only when the thing was drawing current, so I threw caution to the wind and replaced both transistors. The two diodes, the two resistors and the caps all tested within tolerance.







Switch on again, and it's cured!

In the above picture, you can see two wire links across F152 and F153, where there was place for a couple of fuses. The wire links are original, so the fuses were obviously deemed unnecessary, relying on the non-replaceable thermal fuse in the transformer...

Not sure I like that idea much....

33 comments:

  1. I found similar problems with the KEF PSx000 series subwoofers and Celestion which were identical inside. Lots of electrolytics next to resistor dropper resistors. Several small transistors not doing what they should. Fitting proper regulators on big heat-sinks as well as the trannies worked wonders. Many electrolytics were replaced with high temperature ones. So far after a few years no returns... :-) Andy 2.

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  2. I have the same issue. I'll pop mine open and have a look!

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  3. Great post. Mine shows exactly the same heat problem. I'm more of a software guy these days, so what would you replace the diodes D151 and D152 with as I intend to replace ALL of the components around the scorched bit of PCB? I'm guessing something like 1N914.

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    1. Mine checked out OK. I think the scorching is caused t=by the transistors being faulty, rather than the diodes being poorly rated. They're nothing special, a 1N4007 or something would probably suffice...

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  4. Thanks for this post. I've just replaced my transistors, and my random distant thunder type noises have disappeared.

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  5. My Transformer also hums, and probably needs replacing. Is there a compatible transformer available?

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    1. Measure it's output voltage underload , and get something sutably sized from your local RS/Farnell etc ... I doubt Tannoy supply parts, but maybe worth a go. Note if you are fitting a replacement transformer, you must provide some protection fuses, as a replacement is unlikely to have the same protection built in as the original.

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  6. Hi Andy

    In regards to your comment about the wire links across F152 and 153, what fuse amp ratings would you replace the wire links with. I have the same fault that I'm fixing and think that protecting with 2 fuses is the way to go.

    Thanks for your super-helpful post, I eagerly await your reply!
    :-)

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    1. A wise move. I'd measure the current under load, double the measured value, and use a time-lag fuse to cope with the inrush to the caps.... As a guess 1.5A?

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  7. My mate switched voltage on back of sub now won't turn on can it be fixed?

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  8. I suspect that will have killed the transformer, and probably some other damage. Check the output of the transformer.

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  9. Stumbled over this post as have had a similar issue and sure enough the transistor at 152 looks like it's run hot. Found a1015 transistors and C1815 on eBay. They the right replacements? Look right! Thanks!

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    1. Most manufactturers don't put the "2S" prefix on the device, so they are probably correct.... HOWEVER ... I don't buy transistors on eBay unless as an absolute last resort! I've had far too many fakes. Try to find a reputable supplier. RS/CPC/Farnell/Mouser/Digikey etc etc...

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  10. thank you. replaced a1015, C1815 - no issues so far.

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  11. Just a quick tank you for this post. I was having the same problem with an SFX set I recently picked up cheap. A nice easy fix and my bargain speakers are ready for a few years of abuse.

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  12. A huge thank you for this post, I bought this sub-woofer second hand and thought I had bought a lemon. The transistors or mine hadn't visibly change colour but after getting random cracks and noise with no inputs decided to swap them for A1015, C1815 from ebay and has been working perfectly ever since. Even with my terrible soldering!

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  13. Thanks for this. I'm another user who experienced the same issue and your blog saved my sub from undue replacement / expensive repair bill

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  14. Thanks so much for this Andy. Am a complete novice when it comes to soldering, but a few pence worth of transistors (and a bit of time and patience) and the intermittent thundering has been banished from my sub! Tips: If you're struggling to get the backplate off after removing the screws, just take the speaker out from the underside and put your hand inside to push the plate out. I also found that the white push-fit connector had been 'glued' into the socket, but was able to carefully scrape off the dried glue and gently work it free. Well worth disconnecting it, as it makes working on the board much easier (you'll want it as flat as possible). As previously commented, my part numbers were A1015 and C1815 (also from ebay).

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  15. Hi everybody! I had the same problem on 2 subwoofers , replaced the 2 transistors and they are back running again... the only problem i see on both is that i can't turn up the volume too much... i mean ~ 40 % with signal supplied from an Ipad is the maximum i can go without distorsions. Anything above this will make them sound very poor... I need to mention that i test just the subwoofer(no other speaker playing, so i listen just the bass), and it doesn't sound loud for me, it sounds quite low... Or do i have too many expectations from this subwoofer?

    Anybody which has this, can you please supply signal from a phone / tablet , rise the signal from the device to maximum, set the LPF to 1/4 or 1/2 of the stroke and then please tell me how much can you rise the volume until sound gets distorted? At this volume how is the bass(if you listen just the subwoofer)?

    Thank you all!

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  16. Thanks to this information I was able to repair my Tannoy 5.1 sub aswell. It was showing the same heat damage around this set of components. Replaced A1015 and C1815 with components from ebay, £1 for 10 transistors. Soldering was a little tight to get to but with an extra pair of hands was easy enough :)

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    1. Turns out my celebration was early :( After a couple of weeks the pops and thunder returned. Any suggestion what could cause this to recur would be gratefully received :) I haven't got around to replacing them again just yet in case it is something else causing the problem.

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    2. Replace them again, and see what happens. I won't buy semi-conductors from eBay. There are too many fakes out there.

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    3. Will give it a go later today :) It could be that they are junk, I had issues finding replacements from elsewhere :(

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  17. Hello. I need a picture of the electronics component inside. My tannoy msub10 was burning some resistors, transistors etc on the circuit board and i can not be able to buy that components because i do not know wich one is. I need a macro picture from that!. Can you?

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    1. This isn't an msub10 ... ??

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    2. I know, but the components are similar on the board...that's what i see. The numbers of transistors correspond!

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    3. These are the only photos I have.

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  18. I too have this issue with the SFX sub and find the same deterioration on the pcb, but I am struggling to find the exact replacements transistors for this job, particularly for the 2SC1015. Whilst competent to desolder and replace these components, I am not so technically minded as to quite figure this part out. Does anyone have any suggestions?

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  19. I too have the SFX issue as above, with similar deterioration of the transistors, but I'm struggling to find exact replacements for these components, especially the 2SC1015. Whilst being competent to desolder and replace them, I'm not quite so technically adept at determining suitable alternatives. Can anyone help? I'm UK based and cannot find anything that looks similar on RS/Farnell sites etc. Thanks in anticipation

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    1. Ugh ... it appears to have vanished. May need to rely on the vagaries of eBay ... and I hate that ... https://www.ebay.co.uk/itm/2SA1015-2SC1815-Npn-Pnp-50V-0-15A-0-4W-Pair-or-Individually-5-10-20-50-Pcs/223535558475?hash=item340bc1ef4b:m:mNnYj7nSKgkbTC3h6NJDLEA

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  20. Wow - thanks so much! - and I even trawled ebay myself and found nothing. Sterling work! At least you can buy these in a quantity, so if there is a quality issue, you've got them on hand to replace.
    BTW - thanks for your excellent blog and all the tech information!!

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    1. You're welcome Dingo. I dislike buying components on eBay, there are so many fakes out there. Sometimes there's no option. Beings as these are only just obsolete, I'd hope they're OK. If this continues, I should get the Jaeger book out and find something to fit Good luck!

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