K8060 problam - and previous posting deleted?

Kits Audio Hi Fi Projects
1

Hi,

I wrote to you about a month ago regarding problems with 2 K8060’s blowing fuses and/or burning out resistors.

The reply I got from support wasn’t very helpful, but when I complained it seems the post and my account were deleted?

I need help with these kits, particularly with what I may have done to cause these specific resistors to blow, and I repeat I have performed all the instructions listed in the kits. It seems like my problems are similar to those experienced by other people too, so surely it would be in everyone’s best interests to post some trouble-shooting tips to support the build manual.

Can you restore my original post and help us all with an answer please?

If not, unfortunately I will have to return the boards as faulty and post a formal complaint on the retailer (Maplin) website, which I really don’t want to do because from other posts it seems that once these are built and working correctly people are very happy with them.

I look forward to receiving your answer.

Tony

2

Dear sir,

Some accounts are maybe deleted due to spam problems, sorry about that.
You may always post your problem again, but we are not able to solve all problems trough mail or forum, so maybe you can send your defective kit via your dealer (or directly) to us for repair.

3

Hello,

I have exactly the same problem with my kit everything is correctly sold but after having powered it on the R19 and R20 melt. How can I check that nothing else has been destoyed?

Regards

Ange

4

Hello,

I’ve found the issue I’ve inverted TIP147 and TIP142 what components could have suffer from this mistake?

regards

5

In that case, we replace all transistors. It is the cheapest, fastest and most reliable way to solve this problem.

6

To darthhog:

Sorry, we cannot restore deleted posts.
Please check forum rules regarding language and attitude.
If the replies you got were not helpful, then maybe you should return your kits for inspection/repair.
You can return them to:

Velleman Kit Tech. Dept.
Legen Heirweg 33
9890 Gavere
Belgium

7

Hi,

well it seems we may have stumbled upon the answer…

I built two kits, one after the other, except for final assembly to the heatsink when I did the two side by side. Looking at the assembled kits I have two TIP142’s (T8) on one board and the two TIP147’s (T7) on the other.

This is really disappointing - the manual gives no warning of this potentially very easy mistake, in fact looking at the copper side of the boards it looks exactly like the pin orientation is reversed as you would expect if using two identical power transistors in mirror-image configuration. I simply thought I was mounting four identical power transistors and the manual did nothing (apart from an obscure and easily overlooked reference in the title on page 12) to suggest otherwise, in fact since it generally groups both transistors together in the text it strongly suggests to the reader that they are interchangeable…

So if I read the Velleman answer correctly, I now need to get (and fit) replacements for all 16 transistors (two boards), and R5, 6, 16, 17 on the burnt-out board.

How do I do this, and will you update the manual or add in a warning sheet with new kits so others don’t make the same very easy mistake?

Thanks,

8

We understand that you are frustrated because of the mistake you made, but blaming the manual is just too easy. Not only does the manual indicate the transistor references, also on the PCB their references are printed. Sometimes ‘assuming’ is just not good enough. This is a very popular kit, thousands have been sold, with almost zero returns, which learns us that the manual is quite OK.
I’m sure you can get replacement transistors from Maplin or any other UK electronics distributors.
We’re not saying that all transistors will be defective, but our experience learns us that it is much quicker to simply replace them all instead of starting to desolder and testing them individually. If you overlook one defective transistor, it might take out all others at the next power on.

9

I disagree.

Posts on this and other forums suggests that this happens often. This is not helped by the fact that the manual warns the user specifically about positioning of diodes, electrolytic capacitors, the LED and T6. It is therefore easy to assume (because the text doesn’t warn the user otherwise) that there are no special considerations for T7 and T8, which is more than a little ironic considering that these two in particular if mounted incorrectly will do the most damage!

I would imagine you don’t just want some or most of your customers to be happy - you want ALL of them to be happy! In the industry I work in clarity is key, and in this case your instructions are more than a little open to misinterpretation. I am not asking you to agree - I am telling you, as a consumer, that is the case.

In a similar vein, I would expect you to volunteer to send out replacement parts free of charge to anyone affected by this omission - that would be the right thing to do.

Perhaps (I hope you will not delete this post this time) any other customers with similar problems would like to comment and we can see how many agree with me or you?

Best,

Tony

10

There are no errors in the manual, the problem is clearly caused by an assembly error you’ve made. You claim it is caused by the manual not being clear, that’s an opinion and we have no problem with that. If a kit is returned and the problem is caused by a manufacturing error or defective parts, we fix it for free. I’m sure you’ll understand that we cannot start sending out free replacement parts to solve problems caused by user error. One final note: I’m sure all customers will agree to receive free parts, don’t bother asking…

11

OK - for the benefit of my fellow builders, particularly those in the UK sourcing additional components (transformer and heatsink) through Maplin…

I have finally got the kit working and I’m really pleased with it. The bits that I’ve had to work out for myself are:

The Maplin heatsink is too short to mount the power transistors T7 and T8 as indicated by the manual. To get aound this I mounted the transistor connectors to the REAR of the board with the long side soldered into the PCB and the short side facing inwards, so if you look at it from the side it looks like:

[color=#FFFFFF]-----[/color][color=#000000]-------------------[/color][color=#FFFFFF]-----[/color]
[color=#FFFFFF]------[/color][color=#000000]|[/color][color=#FFFFFF]------------[/color][color=#000000]|[/color][color=#FFFFFF]------[/color]

Then mount the power transistors to the connectors so that the finished assembly looks like this:

[color=#FFFFFF]-----[/color][color=#000000]-------------------[/color][color=#FFFFFF]-----[/color]
[color=#FFFFFF]-[/color][color=#000000]===|[/color][color=#FFFFFF]-------------[/color][color=#000000]|===[/color][color=#FFFFFF]-[/color]

Then work out the position for your drill holes on the heatsink. To make it that little bit better I also mounted the LED underneath the board and matched it with a hole in the heatsink to give a visual indication of power on/off from the exterior.

To reiterate the points made above in this thread - be really careful to spot the difference in the two power transistors T7 and T8 (TIP147 and TIP142) before mounting, and double-check before powering up. Anything wrong in this area will again blow the 1a fuse and probably damage other transistors, although there will be more on this when I rebuild the non-burnt-out board to see if the fuse protected it. DON’T be tempted to use a higher-rated fuse - I did and set fire to four resistors!

Transformer connections for the Maplin unit are as marked on the board, working anti-clockwise - Y - Yellow, R - Red, B - Blue, G - Green. This has the effect of shorting Red and Green as a centre-tap, giving c70v AC between Yellow and Blue, which you can test off the board to be safe. If you use the 1a slow-blow fuse specified when testing, connecting Red and Green together and measuring across Blue and Yellow will NOT blow the fuse, but an incorrect configuration will - a good way to test before committing power to the board.

OK - you’ve tested and connected the transformer, you’ve double-checked the power transistors and you’ve run over everything obvious with a multimeter to check for potential shorts. Obvious ones are between the pins of the power transistors, from the metal body of the power transistors to the heatsink, signal in/ground, speaker out/ground and +40v/-40v on the end of the rectifier diodes. Ensure VR1 (bias adjustment) is turned fully anti-clockwise, and that nothing is connected to either input or speaker terminals.

Connect AC power and check the LED - it should light and stay lit. There should be no discernable hum coming from the transformer. If the LED lights and then immediately goes out the fuse has blown - re-read the above notes on the transformer and the power transistors first because that was the cause of the problem in my case.

Next check the voltage across R19. It should be zero or close to zero. Turn VR1 up and the reading from your tester should start to rise, slowly at first and then much more quickly. If you’re lucky at around the 9 o’clock position it should rapidly rise above 10mV - wind it back to 10mV and let it rest for a few minutes before giving yourself a pat on the back for a job well done!

If not, as it did with me first time around, the maximum voltage I could reach with VR1 turned all the way to the right was 3.3mV. This again seems to be quite common.

I started by checking for continuity between all the components using the circuit schematic at the back of the manual. Eventually I traced the fault to a dry joint on the collector of T8 - found by checking resistance between the +40v at the top of the rectifier diode and the middle pin of T8. Resoldered the joint, re-assembled the board back to the heatsink, tested again at R19 and easily found 10mV. Hey presto - the amplifier now works exactly as I wished for.

So, in summary:

Reposition the power transistor connectors as described to make the whole thing fit on the Maplin heatsink;
Make sure you mount the correct power transistor to the right connector T7 is a TIP147, T8 is a TIP142;
Wire up the transformer as described - the colour letters on the board are correct;
If the fuse blows the transformer and/or power transistors are the most likely candidates - look there first;
If you cannot get 10mV over R19 refer to the circuit diagram in the manual and start working component to component checking for continuity.

Stay with it - you will get there and when you do, it’ll all be worth it! :wink:

All the best,

Tony

12

I had the same problem with R19 and R20 melting but I have TIP147 and TIP142 the right way round, what’s going on here?

13

Hi,

sorry to hear you’re having problems. I’m just about to build yet another board after one of mine fried itself - probably as a consequence of being in the sun for most of a day at a school fete and therefore overheating. Something went bad however and the familiar smell of burning electronics filled the garage for weeks after!

That said, up to that point I’d been using the amps to drive powered monitors for our (very loud) live band - and they’d performed really well, so all I can say is stick with it and you’ll be pleased with the results.

As to your problem, the only thing that I can think of to cause those resistors to melt/burn is running the high output power from the TIP’s back through them, that or somehow getting them to be in the middle of the +/- 40v and ground. Logically they melt when they are asked to handle much more power than they’re built for, and that means something in the build is wrong, or you’ve managed to short something inadvertently. I’m not looking at one of the boards now but from memory the centre of the board carries 0 volts; the outside the higher positive and negative voltages that drive the loudspeaker output in its two phases. Looking at the melted resistors if they are melted on just one side (of the board) then I’d tend to suspect you’ve accidentally mis-positioned or shorted something close to that area. If it’s both sides then it’s more likely to be a build error and transistors are either not oriented the right way or transposed from one side to the other. A last check should be that you’ve not somehow managed to get a dead short across the speaker terminals or wired up the short-circuit protection incorrectly such that it causes a dead short - both will give a path of high voltages across those resistors.

As you’ll see from my comments above Velleman don’t help an awful lot with support over the wire; preferring that you send the board back to them. My personal experience is that if you sit down and work through it methodically, with a multimeter (preferably one that can tell you if PNP and NPN transistors are behaving correctly), you’ll find the problem sooner yourself.

One last word of warning however - there is a fair amount of talk on these pages that if the cause of resistors melting is transistors, then there are probably several that are damaged and you might be better replacing them all. The alternative is that you find and fix one, but the damage lying in wait elsewhere causes it (or something else) to pop as soon as you power it up after the repair…

And one final thing - were you running the recommended 1a slow-blow fuse? I never got to find out whether that had actually protected the components on the board that hadn’t caught fire, but in principal if you’ve got the right fuse in it should cut the power well before anything melts?

Anyway, keep at it, and best of luck,

Tony

14

Hi, no I didn’t use the fuse as I was still testing it on the bench and so didn’t have a safe way of housing it.

I think it’s something to do with the transistors but the only place I can get one is online so with postage it comes to about £13 so I might aswell buy a new one from Maplin.

Oh yeh and I saw the post on here about the 34V torrodial and mine was the same could this be the problem?

Thanks
Boscoe

15

Hi Boscoe,

for power I used one of these:

maplin.co.uk/Module.aspx?ModuleNo=218978

which works really well - thoroughly recommended.

As far as the transformer goes, as long and you have wired the colours up correctly and got the diodes in the right direction then you should be fine - as I said in the long post try (carefully! - and with a 1a slow-blow fuse in place) connecting the Red and Green wires together then powering up with a tester (set to AC with a range of 100v) across Yellow and Blue - you should see 70v AC - if that’s the case then the transformer is as it should be. It’s not beyond the realms of possibility however that you have got a dud - I remember reading elsewhere on this forum that one of us had precisely that problem with these symptoms.

Otherwise, I think what you’re doing is what I would do - new kit, build it slowly and methodically, double-and triple-checking the type and pin orientation for all transistors, and if you’re building it to the Maplin heatsink then be extra careful in the mounting of the power transistors as it’s very tight and easy to short them accidentally to the heatsink. The same for the temperature sensing transistor buried in the heatsink itself. To be double-sure test for continuity at each stage and particularly with the big transistors to make sure that everything that should be connected is, and everything that shouldn’t be isn’t - if that makes sense!!

Lastly, on first power-up make sure you have an 8-ohm speaker connected BEFORE you power-up (test the ersistance across the speaker terminals to be sure) and let the amp LED go out before disconnecting - I know it is supposed to have short-circuit protection but I don’t trust it!

Good luck and let us all know how you get on.

Tony

16

Okay thanks for the help and I won’t be building one for awhile now as I don’t have the money ( I know it’s only £15!!), just out of interest what is the light bulb on first power up supposed to do?

Thanks

Boscoe

17

Lightbulb prevents damage to kit when an assembly error has been made.