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Old 06-08-2012, 01:52 PM   #1
midibob
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Default Vox mini 3 amp

Hi all,

Been grappling with this one for a while and no success so far.

These little guitar amps are rated at 3W and are quite nice, good sounding busking or bedroom amps.
I have a number of these with blown output chips and thought they would be quite a simple repair!!

On inspection I found that the chips were micro smd 9 ball WLCSP types. They are 1.2mm square and you need a microscope to see them.
Trouble is the type code bears no relevance to anything I can find. No IC manufacturers I've contacted so far have been able to identify the type number 'BP27'.

There are so many of these class D amp devices available with different specs and gains that it's impossible to guess which one would be the correct replacement.
I've tried the Vox forum with no joy either. Schematics are non existent too.

Pity it's not dodgy caps, easy stuff in comparison.

Midibob
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Old 06-08-2012, 02:50 PM   #2
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Default Re: Vox mini 3 amp

http://www.digikey.com/product-searc...-audio/2556583

Filter by Supplier Device Package , 9-uSMD since you say they have 9 contacts.

Could it be one of the Boomer series chips ?

http://www.digikey.com/product-detai...TLX-ND/1871632
http://www.digikey.com/product-detai...DKR-ND/1207570

etc ?
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Old 06-08-2012, 03:48 PM   #3
midibob
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Default Re: Vox mini 3 amp

Hi,

Thanks for the reply.
No, I don't think that one is the direct replacement. Only going by the application sheet which shows two resistors connected to the inputs whereas the vox has direct cap coupling. This is to select the gain I suspect but some of these chips have switched selectable gain too depending on whether one of the pins is grounded or not.
The techies at Texas Instruments did say it might be one of theirs with that marking (BP27) but couldn't confirm one way or the other or tell me what the actual device number was?

As I say there are so many variations and I can't afford to test them for suitability.
Other devices that could fit the bill are :-
SSM2377 (Analog Devices)
SSM2335
SSM2315
HT6845 (Heroic)
ALC103 (Realtek)
SA58672 (NXP)
AAT5101 (AAT)
MP1740 (MPS)
BD5460 (Rohm)

I'm sure there are plenty more from other manufacturers.
It's a nightmare....

Midibob
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Old 06-08-2012, 07:08 PM   #4
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Default Re: Vox mini 3 amp

bob, is there a FCC ID somewhere on or in the device?
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Old 06-09-2012, 04:44 AM   #5
midibob
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Default Re: Vox mini 3 amp

Ah, never thought of that. What a good idea.

Well just looked and unfortunately I can't find one?
All I can find is that it conforms to Part 15.
The user manual states this but no further detail. Also there is a picture of the back plate which has the conformity stuff on it which again just states Part 15.

Not sure how I can find it on the FCC website without it.

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Old 06-09-2012, 06:22 AM   #6
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Default Re: Vox mini 3 amp

thought so. i saw the back plate too but no ID.

can you you post a basic pinout with some surrounding components maybe?
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Old 06-09-2012, 11:24 AM   #7
midibob
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Default Re: Vox mini 3 amp

OK, lets see how this goes.

The pinout I've had to do with Windoze Paint so it's a bit rough. it's drawn as you would be looking from the topside.

IC3 is the chip in question which I've already removed.

The last picture is of the chip, not easy to read I'm afraid as I don't have access to microscope as yet.

Midibob
Attached Images
File Type: jpg mini-P1000706.JPG (594.5 KB, 232 views)
File Type: jpg mini-P1000708.JPG (394.0 KB, 212 views)
File Type: jpg smd1.jpg (82.0 KB, 186 views)
File Type: jpg Pinout.jpg (16.9 KB, 159 views)

Last edited by midibob; 06-09-2012 at 11:32 AM..
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Old 06-09-2012, 10:56 PM   #8
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Default Re: Vox mini 3 amp

Hello Bob. This part looks to be a Texas Instruments TPA2039D1. The pinout and specs match: http://www.ti.com/lit/ds/symlink/tpa2039d1.pdf
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Old 06-10-2012, 05:00 AM   #9
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Default Re: Vox mini 3 amp

Yes that does look quite good.
I did have a TPA2034 on my short list but not this one for some reason?

Next problem is trying to find somewhere to purchase them in the UK?
I've looked at Farnell, RS components, Rapid and Digi-key so far. Digi-key is the only one that lists them and they don't have any!

Oh well, the search goes on.

Midibob
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Old 06-10-2012, 06:02 AM   #10
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Default Re: Vox mini 3 amp

bob,
you can order free samples (up to 3 per part IIRC) directly from TI.
i've found their sampling policy to be quite generous, and no shipping charges apply.
(as long as you don't overdo it i suppose.)
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Old 06-10-2012, 11:29 AM   #11
midibob
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Default Re: Vox mini 3 amp

Another brilliant idea.
At least I'll be able to prove they are OK for direct replacement then I can concentrate on ordering some.

I've found Mouser have them in stock but they are about 3 times the price in small numbers. Still, cross that bridge when we get there.

Thanks to all and watch this space.
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Old 07-08-2012, 10:00 AM   #12
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Default Re: Vox mini 3 amp

Just thought I'd update the progress on this one.

As you may suspect there's good news and bad news....

Starting with the good.
The chips arrived from Texas very quickly and that fitted in nicely with the arrival of my microscope. So it was all systems go.

And then the bad...
1st problem was chip number 1 decided to make a leap for freedom as I was attempting to position it and was never seen again!!! The slightest twitch of the hand and these things are gone.
Now the 2nd chip once positioned didn't want to connect all the bumps to the circuit board. After many failed attempts the device needed reballing. It is possible to do this by hand but only just.

Just for info under board preheating was used along with a hot air soldering station sticking as close to the temperature profile as possible.

I'm, beginning to come round to to the fact that as a DIY project this isn't viable which is a shame.

Haven't given up yet though.
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Old 07-08-2012, 01:29 PM   #13
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Default Re: Vox mini 3 amp

I would just say screw it and wire in a chip that's more easily handled by a human. There's a ton of space on the board, actually, why they went with a device that small is beyond me.
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Old 07-09-2012, 03:27 PM   #14
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Default Re: Vox mini 3 amp

Yep, I was thinking about that. Even a SOIC type package would be workable although you would then need some kind of adapter board. There are adapters available for conversion between various footprints but I've not seen one for WLCSP??

I suspect built in obsolescence could be one reason as it's the most likely device to fail on the board and only a specialist repair shop would attempt it and I dread to think at what cost.

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Old 07-19-2012, 03:00 PM   #15
midibob
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Default Re: Vox mini 3 amp

Geronimo!!

Well had a few days off to get away from it and tried again.
This time it worked although it's not exactly flat on the board but all the balls have soldered to the tracks.

Plugged in with some trepidation as I thought the poor old chip would have self destructed after the amount of failed attempts, but no, it appears to be working fine.
So it would seem that the IC is the correct one although I've yet to compare it against another working amp, but it does sound loud enough.
Just got to hope I haven't aged the caps with all the heat cycling!!!

I'm well chuffed.
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Old 10-28-2012, 09:30 AM   #16
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Default Re: Vox mini 3 amp

Hello Midibob . I too have a Vox mini 3 in pieces , and with some weak logic , and the powerfull evidence of your repair success , suspect I have the same problem . More weak logic and no knowledge lead me to ask whether it would be remotely possible to try and do this repair with hairdryer , thermometer , powerful optics and bloodymindedness .I have been on a short learning curve and never dreamt any of the micro repairs and components used were within human grasp . How stupid of me . Please get in touch if you could offer some advice . many thanks , mic . I have tried to contact direct , and leave my email , but dosn't seem to work .

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Old 10-28-2012, 03:03 PM   #17
midibob
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Default Re: Vox mini 3 amp

Hi Mic,

I wouldn't attempt a repair using anything but a proper SMD heat gun and an under board pre-heater. Without proper temperature regulation and directed airflow you'll more than likely ruin the board. The tracks under the chip are extremely fragile and if damaged a 'normal' repair would become impossible.

Having said that I am currently working on producing a daughter board which can be retro fitted with conventional tools and the users normal eyesight!!
It's not at the production stage just yet as I haven't had time.
Also, due to the work involved I'm wondering how many might benefit so it might depend how much interest it generates. You are only the second person so far.

Out of interest do you know what caused the o/p chip to blow? I'm suspecting a lot of them are caused by folks messing around with the speakers although I can't be sure.

You can confirm the chips demise by testing the resistance of either of the speaker leads (with the speaker disconnected) to ground. You will usually find one of them is around 35 ohms whereas they should both be >200K ohms. Obviously make sure it's switched off first.

Hope that's useful.
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Old 11-17-2012, 02:20 PM   #18
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Default Re: Vox mini 3 amp

Hi I have the same problem with you mini3, lights but no sound, if I use the headphone listening algo.quiero know if they have reached a solution or at least the parallel circuit to integrate mensionan "Ic3". excuse my English as I use google translator.

kevin of Argentina
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Old 11-18-2012, 05:40 AM   #19
midibob
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Default Re: Vox mini 3 amp

Hi Kevin,

Bienvenido to the forum.
No problem with the English 'mi español es atroz' !!

I see there are more of these amps failing but this is the first report I've seen from another country. Do you know what caused the output chip to blow?

With regards to the parallel circuit I haven't done any more work on it due to lack of spare time. Maybe in a few weeks I can start producing the PCB's as I have the layout sorted.

'espero que esto traduzca bueno'

Midibob
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Old 11-19-2012, 11:27 AM   #20
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Default Re: Vox mini 3 amp

he seems to was for the effects much gancia or something from what I've read in other forums of people with the same problema.aca with a friend are trying to do a parallel output using LM380 conosco not much about it because it does not but if I am electronic cash hereby publish it on this forum and if I quite understand your mensage.saludos from Argentina
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