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franjam's κDCX build for non-engineers & the inexperienced

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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby amb » January 20th, 2018, 6:08 am

I replied to both your messages. Please check to make sure they didn’t end up in your spam box.
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby franjam » January 31st, 2018, 1:55 am

Hi TI,

As you know I'm awaiting the imminent arrival of the kDCX PCB, in the meantime a problem has arisen with my DCX and I thought I'd post here as much as anywhere else, I hope that's ok :

I started getting an intermittent rustling sound in the left hand mid/bass driver in the last few days ; this morning when I switched on the system and the "rustling has become more or less permanent but it varies in intensity from fairly quiet to a sound like leaves in a high wind.

I have isolated this by switching off elements preceding the DCX including removing the the input cables, the sound persists coming from the left bass driver which corresponds to the first analogue output.
Could this be a dried out cap?, ( the sound has just ceased , I'm listening to the radio). I'm obviously hoping the kDCK will cure this but I would like to understand what the problem is?

Thanks.

EDIT: The sound is not volume dependent obviously and seems to be completely random.
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby amb » January 31st, 2018, 5:10 am

Could be dried out caps (how old is your DCX2496)? But just as likely one or more opamps became noisy.
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby franjam » January 31st, 2018, 5:45 am

My model is the january 2015 model so 3 years old exactly ; I've had it myself for about a year and it's seen almost daily use since then....but I would have thought the caps would last longer than that..
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby amb » January 31st, 2018, 6:00 am

Yeah it seems too new to be a capacitor issue. Btw, read your PM.
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby franjam » February 2nd, 2018, 2:24 am

Ok I'm going to talk about the kDCX build but first my DCX is getting worse! : yesterday the sound cut out and the display screen flickered from blank to the DCX startup screen, then it all came back. I am worried that this may be more than the analogue pcb, any thoughts..?

EDIT: the only thing I have been able to find resembling this fault talks about faulty cables and Behringer cutting corners in connection quality ; I did recap the PSU recently so I'll open it and check all connections.

POST EDIT 7 Feb 2018: This particular problem turned out to be a connection fault between the PSU and the DSP PCB. I had recently re-capped the PSU and obviously I disturbed something on the PCB socket. If one reads around on this problem of a faulty display screen, different things are suggested, including doing a re-set or replacing the EEPROM chip or re- flashing it, all of which I was close to trying. I can be a little impatient and quickly imagine that the problem is major ; what I have learnt is that the problem is often a simple one and therefore so is the cure. As the problem started after my recent re-cap of the PSU there was a good chance the fault was somewhere there, ( as Ti so rightly suggested, credit where it's due ;) ). I therefore checked voltages, resoldered the socket pins on the PCB, checked the cable and hey presto I got my DCX back! :D So thanks to Ti for the suggestions and the message to myself and you all is : don't panic! take your time , be patient, be methodical and 90% of the time the solution will be straightforward. :)
Of course that leaves the other 10%...... :o :shock: :geek: :P
Last edited by franjam on February 7th, 2018, 12:52 am, edited 1 time in total.
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby franjam » February 2nd, 2018, 3:31 am

Ok, so the kDCX pcb arrived at last, only took about 30 days to get here, thankyou USPS. :evil:

Obviously champing at the bit I started immediately with o78 and o79. First time I've touched SMD's and they are SMALL!! So if like me you not done this kind of build before make sure you have everything in Ti's tool list 'cos you will need it all. A good magnifying glass on a stand is indispensable especially if you're eyesight is not what it was ;) . It's easy to put too much solder, so a little is really a little and if you can buy extra resistors do, 'cos that bit about not finding them again is true :lol: I was a little nervous when I started and I found that if you squeeze too tight with your tweezers then that incy- wincy little resistor does tend to pop out and fly off somewhere. You then have to order one smd resistor from Farnell to finish your pcb :D . So my advice is, avoid that, buy a couple more ;) .

O78 O79 resized.jpg


Ok it isn't all perfectly sraight but hey first time :P

I then started on the main board. Those FETs are also TINY!! :o :shock: I really was not prepared for the sheer tinyness of everything, so again, be careful when you see photos on this forum, they are invariably close-ups ; imagine very small parts, then divide that idea by ten.... :lol: Anyway I soldiered on, held my breath, sweated a little, put too much solder, then not enough and gradually after about 18 FETs and 20 odd op-amps I started to get the hang of it :D . I was almost sorry it was over, he lied. I could now move on to the endless amount of resistors :o .

On a slightly more serious note, you do have to be extremely methodical : there are a lot of (VERY) small parts. I am following the parts printout, taking one packet out at a time, then one part out of its packaging at a time. When you get to the resistors and once you understand the layout you can start to solder in series, one value at a time.

op-amps and FETS resized.jpg


This brings me to a question for Ti, or anyone else with experience for that matter..

On some of the resistors the solder flows through the hole and bulges out on the top side, sometimes a lot. on others it doesn't necessarily go through and "blobs a bit round the leg of the resistor. I am using Loctite 0.56mm 60/40 solder. It is difficult to get a consistent thing going and I've not come across this before..any suggestions?

Something else that bothered me at the time especially on the o78/79 pcb, as I was fiddling around alot trying to get it right, the chip and pcb were gatting quite hot, same for the FETs, it occurred to me that I may "fry" the chips, is that a possibility ?
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby amb » February 2nd, 2018, 8:48 am

The solder wicking through resistor holes is a matter of how much solder you apply. A little solder and it won’t, but more solder it will because the holes are plated through. If you feel like there is too much of a solder blob (on either side), use a solder sucker to remove some solder and then reflow with just a little fresh solder.

As for “frying” the chips, consider that SMD reflow profile subjects the parts to close to 250°C in an oven for several minutes. The soldering iron tip is hotter than that, but the time duration that you’re heating the part is much shorter (or hopefully so!).
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby franjam » February 5th, 2018, 9:58 am

Hi TI,
I'm going to post my build with various details and pics but I am currently on final tests and have a problem.

(Got my DCX back it was a PSU ribbon connection thing..see previous edit.... :) ), The kDCX is built and all is well until I get to the J13 test : pins 7 reads -15.2mV and pin 8 reads +50.9mv !? the others are good at 2.5v, I have no idea where to look for the problem, the circuit diagram says they go to X13 7 and X13 8 which is Input B OPA1632 outputs (U2B) as far as I can tell but where do I go from here? :?
U2B legs read :B
1)1.23V
2)2.5V
3)14.17V
4)-15 mV
5)48.5mV
6)-14.05V
7) 0.1mV
8)-18.2mV
It's as if U2B pins 4) and 5) lead to J13 pins 7 and 8....?

Thanks.

EDIT: Solved it!!! I'd missed the soldering on one side of the op-amp :oops: , don't know how but it just goes to show.... :) So onward with the rest of the tests.....; :geek:
Last edited by franjam on February 7th, 2018, 1:00 am, edited 2 times in total.
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Re: franjam's κDCX build for non-engineers & the inexperienc

Postby franjam » February 5th, 2018, 10:56 am

DC measurements on the XLR outputs are all over the place :cry: AC measurements all good at 0.......cable is in the right way I'm sure...help! the FETs were the first thing I did , they got very hot , maybe I fried them... :| they all read -14.05 mV on pin 1, Q1/2 D-K

readings mV :

Output, pin3, pin2, 3+2

1), -52.4, -61.3, 8.5
2), -27, 33.3, 61
3), 10.7, -3.8, -14.7
4), 9.6, -3.2, -12.7
5), -17.7, 24.7, 42.9
6), 22.1, -15.4, -37.9

All other tests are good. Make any sense to you?
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