Translate

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 2S1815, NPN, and Q152 is it's complementary PNP, a 2SA1015.











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....



*** STOP PRESS *** 12th May 2020.

Many, many people visit this site to look at this page, and, sadly can't find the correct transistors. 

The SCA1015 is obsolete, a KSA1015YTA is still available..  https://uk.rs-online.com/web/p/bjt-bipolar-transistors/8064403. You can try a BC556, but you need to fit it backwards, and reverse pins 1 & 2 (Check the datasheets)
The 2SC1815 is still available from mouser, or you can fit a BC546, again reversing the leads. (Check the datasheets).

These transistors are pushed hard in this application. When (if) I ever see another one, I'll look for a better solution. 

*** STOP PRESS *** 13th January 2021.

PeterCB has been working on his subwoofer, and replaced the 2SA1015 with a TIP32, and the 2SC2818 with a TIP31.

"So I went ahead and replaced the transistors with TIP31C/32C in a TO220 package. Been soak testing for about six hours now, they don't even get warm. The new transistors fit perfectly in place of the originals, just facing the opposite way, see picture"


This has got to be the best solution. An easily available transistor, that's not being pushed beyond it's limits. 

Thanks PeterCB! 

*** STOP PRESS 15th March 2021 ***

Avid reader Springknees has kindly created a schematic of the offending power supply section. 

It can be found at https://www.chantrybarn.co.uk/woofer.php and is reproduced here with permission. 









106 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.

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

    ReplyDelete
  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.

    ReplyDelete
    Replies
    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...

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

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

    ReplyDelete
    Replies
    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.

      Delete
  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!
    :-)

    ReplyDelete
    Replies
    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?

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

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

    ReplyDelete
  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!

    ReplyDelete
    Replies
    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...

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

    ReplyDelete
  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.

    ReplyDelete
  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!

    ReplyDelete
  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

    ReplyDelete
  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).

    ReplyDelete
  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!

    ReplyDelete
  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 :)

    ReplyDelete
    Replies
    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.

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

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

      Delete
    4. See the latest stop press!

      Delete
  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?

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

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

      Delete
    3. These are the only photos I have.

      Delete
    4. Still need images ???
      I have the same issue changed the transistors and 4 weeks later its started again..

      Delete
    5. See the latest Stop Press!

      Delete
  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?

    ReplyDelete
  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

    ReplyDelete
    Replies
    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

      Delete
  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!!

    ReplyDelete
    Replies
    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!

      Delete
  21. I'd just like to add my thanks. I was ready for chucking the speaker in the bin, but found this blog and for £1.98 and a bit of faffy soldering I fixed it.

    ReplyDelete
    Replies
    1. Well done Nick, another saved from landfill !

      Delete
  22. Thanks for your extremely helpful posting. Saved my little sub!

    ReplyDelete
  23. Congratulations nelmdog! Feels good, doesn't it!

    ReplyDelete
  24. Great post, thanks for the help :)

    ReplyDelete
  25. Hi, I have the same speaker, Tannoy SFX, but I'm getting a russelling noise even when speaker not connected to anything.
    Could this solve it?

    ReplyDelete
    Replies
    1. Only one way to find out.... Go for it!

      Delete
  26. Had the same issues, opened it up and traces/pads seem to be non existent around the transistors and peeling up on the capacitor next to it. The board very brown/black. In the case of this sort of damage is it a goner? The subwoofer is 8 years old at this point but still a shame they don't let you buy just this board as I'd feel so guilty dumping such a big speaker

    ReplyDelete
  27. Carefully use some bits of wire to replace the damaged traces... You can do it!

    ReplyDelete
  28. I will give this repair a try as my subwoofer has started to make random thunder sounds.

    ReplyDelete
    Replies
    1. Hi, I don't suppose you live around the Yorkshire area and looking for a little job to do at the moment?

      Delete
  29. Same problem for me. The circuit board doesn't look happy at all. I'll be putting it on ebay with a link to this page so someone can have a go at the repair.

    ReplyDelete
  30. Hi Doz, I've lived without my sub woofer for about a year and a half now, until I found this post! I've decided to have a go at fixing it myself (nothing to lose) but am having trouble sourcing the 2SC1815 NPN and 2SC1015 PNP. Are you able to point me at somewhere I gat get them (where I don't have to buy in bulk)?

    ReplyDelete
  31. Ha, read deeper into the other comments and saw your eBay link, so have bought there! Thanks Doz.

    ReplyDelete
    Replies
    1. Whilst I hate buying parts on ebay, due to the huge number of fakes out there, go for it, and good luck!

      Delete
  32. Same issue on my sub - failed transistors. Those two form a ±12v supply for the analogue board with LPF etc. but they regulate down from ±40v so they are under a fair bit of stress and working close to max power dissipation.

    I changed the 220ohm drop resistors for bigger wattage 560ohm to lighten the load on them and stood them off the board. IR thermostat showed them running cooler. So far so good but a switching regulator would be better.

    Poor design really.

    ReplyDelete
  33. I tried to replace the transistors you mentioned but damaged the board in the process. Can I change the whole amp ? I cant see any with the same connector. Is that a major problem? They seem quite cheap. Thanks

    ReplyDelete
    Replies
    1. That's unfortunate. With a little engineering, I suppose you could fit a different circuit.

      Delete
  34. Hi, another rumbler here! Do you know if the KSA1015YTA is the same (or near enough) as the KSA1015? The former is in stock at Mouser, along with 2SC1815.
    Thanks for the clear explanation and pictures.
    Cheers
    Pete

    ReplyDelete
    Replies
    1. That's the part I listed in the STOP PRESS bit ... looks good from where I'm sat! Good luck!

      Delete
    2. In fact, I ought to make that a bit clearer really...

      Delete
  35. Do you think it would be possible to bypass the internal amp with another one , still using the original inputs and the electronic crossover . Thanks Dave

    ReplyDelete
    Replies
    1. The transistors that fail supply the LT to the x-over, so that would have to be dealt with first, but yes, anything's possible with a little engineering.

      Delete
    2. Thank you very much ... I'll probably buy a nobsound amp and run it off that ..

      Delete
  36. I have replaced these transistors twice now, and the issue keeps coming back. The second time I sat them far from the board in hopes that they wouldn't get so warm.

    Could it be poor quality transistors? I bought them from eBay before your "stop the press" addition. I would buy new from mouser but their delivery charges are crazy and farnell have a 200 piece minimum purchase!

    Any thoughts would be appreciated.

    ReplyDelete
  37. These transistors are for the crossover, yes? Is there a way to bypass the crossover to solve the problem? The signal from my av amp should already be suitable and therefore the crossover is not needed in this setup.

    ReplyDelete
    Replies
    1. No, they're in the power supply. Albeit the power supply to the x-over. See what the output IC is, and get a datasheet for it. You could remove the two transistors, cut the track from the x-over and drop the audio from your amp straight into the output IC.

      Delete
    2. I'll take a look at that. Cheers.

      Delete
  38. I purchased a nobsound 100w sub amp from Ebay and it works brilliantly...given up trying to fix the tannoy amp . Poor components pused to their limits.

    ReplyDelete
  39. Hi, can you fix mine. Obviously not for free 😁👍

    ReplyDelete
  40. Does anyone know a replacement transformer.
    Mine's dead so I can't even check the outputs. TIA... Mart

    ReplyDelete
  41. Very useful site, my sub last night decided it was thunder time ! Taken apart as like pictured my transistors are burnt. Order pleased with Mouse, will update when they arrive and I have fitted

    ReplyDelete
  42. Stumbled across this page as I have the same sub (purchased second hand) with similar crackling/thunder problems. Used the parts suggested in the Stop Press addition and ordered from Mouser. As others have said the postage is pretty steep so I order multiples of each in case I needed to replace again.

    Unfortunately the previous heat abuse had de-laminated the PCB at the Q152 transistor and the two of the tracks fell away. As I didn't have any copper tape to hand I have just used bent the pins of the transistors and soldered to the corresponding components on the board. All seems to be working well so far. Guess only the test of time will tell...

    Thanks for this useful guide. I've manage to fix a nagging issue for not a lot of money. Very happy.

    ReplyDelete
  43. great! had exactly similar problem of random scary "pops" from this sub even with no signal. I ordered KSA1015YTA and KSC1815YTA plus replacements for all but the two big smoothing caps. Had to also repair some lifted/vanished PCB track which didn't make for photogenic soldering!

    didn't work first time but after inspecting carefully I found another dry/lifted joint on a resistor. Repairing this and I now have a decent sub again.

    keep up the good work!

    ReplyDelete
    Replies
    1. Fantastic work! Well done. Another saved from landfill :)

      Delete
  44. Hi Doz, I have nearly the same sub the problem I have is the 800mA fuse keeps blowing I think the transformer has gone. But the problem I am having is finding a replacement as there is no specs of the transformer its identical to the one in your article. If the transformer was working I can then see what voltage the secondary side has and get one to replace it. Do you know the specs of the transformer I know it must be under 50v as the capacitors are 50v.

    ReplyDelete
    Replies
    1. I'm sorry, I don't... several people have asked before. It needs someone with a working one to make a quick measurement.

      Delete
    2. Yeah I thought that might be the case, I will keep digging online and see if I can get some information on it. :)

      Delete
    3. I've slept on this... I think we can make an educated guess... the datasheet for the amplifier IC has examples using a +/-29V supply, so what's the betting that's what is used. so if we spec a 20 - 0 - 20 transformer at 80VA, I think you're in with a good chance. Let me know how you get on.

      Delete
    4. Incidentally, if you this route, I'd fit fuses in those places I mentioned in the original article, and another in the primary, as any replacement transformer is unlikely to have a thermal fuse fitted.

      Delete
  45. Thanks so much for this. Replaced the 2 transistors with some from https://www.ebay.co.uk/itm/2SA1015-2SC1815-Npn-Pnp-50V-0-15A-0-4W-Pair-or-Individually-5-10-20-50-Pcs/223535558475(couldn't stomach £16 postage from mouser) ... Even with my poor solder removal skills that took of part of the track ... No more thunder.

    ReplyDelete
  46. Hi man, can you remember what type of zener diodes are on this board?

    Cheers, Keith

    ReplyDelete
    Replies
    1. Sorry, no. Perhaps someone will read this and comment ... are they not marked?

      Delete
    2. Even with a jewelers loupe I cannot make them out 🤣

      Delete
  47. This comment has been removed by the author.

    ReplyDelete
  48. Hi Doz, thank you so much for providing this information. I have a question - since these 2 transistors perform a fairly basic function supplying the +- 12v to the crossover, would it be ok to substitute some general purpose transistors that can handle a bit more power, such as a TIP31/32? I guess that might need changing some resistor values, that is beyond my knowledge, what do you think, is it worth me trying putting in a TIP31/32 and see what happens? Thanks again, Peter

    ReplyDelete
    Replies
    1. I've mentioned this in the comments above. When I get another in for service, I'll have a look. Haven't seen one for ages now...

      Delete
  49. So I went ahead and replaced the transistors with TIP31C/32C in a TO220 package. Been soak testing for about six hours now, they don't even get warm. The new transistors fit perfectly in place of the originals, just facing the opposite way, see picture here: https://imgur.com/a/ljqoSvJ
    Thanks again Doz for the guidance.

    ReplyDelete
    Replies
    1. Great work PeterCB ... I'll publish that up top if that's ok with you.

      Delete
  50. I replaced both transistors but my resistor R152 has burnt out. What resistor and where do I need to purchase as a replacement?

    ReplyDelete
  51. Hi doz, im a relative novice to this. I replaced both transistors and seemed to be fine for about a day, upon another look I noticed resistor R152 was burnt out and the transistor Q151 was getting very hot. What resistor do I need for R152? Is it a 220 ohm 1/2v 5%?

    ReplyDelete
  52. Looks like the stop press transistors cause resistor burn out. According to Tomtom. Is this going to cause the same problem for everyone?

    ReplyDelete
    Replies
    1. Unlikely ... we need more info.

      Delete
    2. Looks like there's no problem with the Mod.. that's 3 people who have successfully fitted the larger transistors now, with no issue. I think the resistor cooking is due to a further fault.

      Delete
  53. I replaced with A1015 and C1815

    ReplyDelete
    Replies
    1. Thanks for the update.I suspect you have a further fault, not much help I'm afraid. Are the transistors still OK?

      Delete
  54. Thanks very much for the clear and helpful information. Had the rumble and cutting out randomly. I replaced both transistors with tip31/32 as suggested and working perfectly. No rumble or cutouts so far. Less than £3 to repair. Well happy.

    ReplyDelete
    Replies
    1. Well done! Another saved from landill!

      Delete
  55. I just did the TIP31/TIP32 mod and thought all was well. Cone was operating nicely, clean sound... then I noticed a nasty hot smell. The two new TIPs are also roasting hot so there must be another duff component, but without a circuit diagram it's hard to detect the problem, know what component/value to change, or whether just to give up and drop £200+ on a new sub... some of which also have the odd user review about making random rumbling noises!

    ReplyDelete
  56. Hi Andy - Many thanks for your blog, I eventually replaced Q152 with a CV7672 (equivalent to 2N2905A), which has a higher voltage/current specification and a different pin layout. While in the process, I drafted a schematic for the failing circuit - I included some voltage and current measurements that might be useful to anyone interested, it's available for download/printing at:-
    https://www.chantrybarn.co.uk/woofer.php

    ReplyDelete
    Replies
    1. May I put your diagram up here somewhere? Obviously crediting you for the excellent work!

      Delete
    2. No problem - it's Open Source :)

      Delete
  57. Hi Andy - I've updated my schematic to correct a current value. I've also added a guess at part numbers for the zeners and my calculated power dissipations for Q151 and Q152. I also updated my webpage to include some thoughts on power dissipation and transistor selection.

    ReplyDelete