[Presently42]

As the Headwize web-site is currently not functioning and I know of no replacement for the brilliant beta22 threads there, I decided that I would post my request for aid here. Do let me know if there is a more appropriate place.

Having successfully installed all parts on to the boards (a three-channel configuration), I attempted to apply power, using the directions on the Initial Setup page of AMB's beta22 section. I had already verified that the accompanying sigma22 was working correctly. When I applied power, the LEDs on the left (positive) side illuminated whilst those on the right did not. At first, I presumed that I had incorrectly installed them. Soon after I reached this erroneous conclusion, two of the three C16s exhibited signs of malfunction: the tops were thrust outwards and bits of the fluid were ejected. Upon closer inspection, I noticed that these dead caps were installed correctly, but that the lone survivor was backwards. Assuming that some how the polarity had been flipped by the one, I reversed it and plugged in just the surviving board. As soon as power was given, both LEDs on the board lightened — but only for a few moments. Soon, I heard fizzling. Cutting the power, I observed nothing unnatural. I turned on the power again: the left LED lit but the right one did not. Again, C16 fizzled and the top was thrust outwards.

Given these strange tidings, I find myself at a loss for explanation: some how, the negative side must be positive, mustn't it? Why, then, did the right LED lighten, if only briefly? Why haven't the other two polarity-dependant caps displayed the symptoms of death? Are these good question, or do they sadly miss the point?

Thus do I request aid in my quest to complete the project.

 

[FallenAngel]

There are a couple of Beta22 threads on Head-Fi, and a few knowledgeable builders as well (myself kind of excluded as I've only build a one 3-channel Beta22 and had minimal problems with it).

Double check polarity on all electrolytic caps - they have a nasty tendency to blow up (wear goggles when powering up amps for the first time). A single reversed cap might cause a lot of issues.

The best bet is to replace all of the caps that look like they might have been damaged, as well as the LEDs.

Double and triple check all our caps, resistors and transistors for correct mounting - remember how funky the 2SK170/2SJ74 are mounted.

 

[johnwmclean]

Presently42,

I suggest you post good quality pictures as well, all sigma and beta boards. The Pro builders here might have a better idea of the problem. Sorry to hear the news.

 

[linuxworks]

I'll admit to having built a b22 (mine) and made a boo-boo (NOT a mistake, mind you, but just a boo-boo) and, well, when parts 'chains' go down they go down ;(

be prepared to replace a lot of parts. if there was one rail 'going strong' and the other had problems, that can cause a lot of parts to need replacement. its good to know about hakko808 desoldering guns (I used mine more on this project than ever before).

rather than spending a lot of time trying to voltage-narrow it down, I simply chose to replace whole sections that seemed to have gotton hit. once I had all the caps installed correctly and that part was working, the only things that needed replacing were the transistors. and for those, I had quite a few spare sets that, well, weren't spare by the time I was done with the whole thing

get your caps and R's right. they won't 'go' on you once the + is really +and so on

then try to narrow down which of the transistors you need to replace - or just 'go fresh' and get a whole new set and don't even have to -think- about it further (time is worth more than the parts are, I think, and replacing a few or all is almost the same thing).

 

[wolf18t]

Do you have a DMM? Before resoldering any caps just check again the voltage on the negative rail just to be sure you got the right polarity.

In case of ground decoupling caps, remember the positive lead (the longer lead) must be soldered on the ground trace when working on the negative rail side. It is exactly the reverse when working on the positive rail side and it is sometime confusing. You can also check the silkscreen markings on the PCB there should be a "+" or "-" (I just don't remember which are on the B22 PCBs) symbol beside the top solder pad.

 

[dbfreak]

Did you check if your umbilical cord connectors were wired properly?

 

[ephrank]

x2 on posting hi-res photos. Don't use a cameraphone, thats low-res. Use a 5MP or better camera.

 

[Presently42]

I have now lost much face. The fault lay in the connexion between the receptacle on the sigma22 side and the power output terminals — namely, v- was connected to G and G to v-. This explains why v- did not work whilst v+ did.

Other than the three blown C16s, all other caps look fine. The other parts also look to be correct, though there is no telling with any of them save the rs, which seem to measure correctly, save a few, which I am presuming are in parallel with others (the circuit is, for me, too complex to discern easily what is in parallel or series with what).

As to measuring voltages, I decided that I would not turn on the power again until I was sure that I would not cause more damage knowingly.

Concerning the photos, I'm not sure of what I should take a picture: the tops of the boards don't seem to tell me much; perhaps the bottoms should be the subjects of the compositions? I don't think I have any good digital cameras; only my camcorder. I shall have to test a crappy digital camera that I do own.

Sorry for having taken so long to respond. And thanks much for rendering assistance to one such as myself.

 

[johnwmclean]

Dang, Presently42 - if there’s one thing to check, double check and check again it’d be the V- V+ and G wiring...

 

[Presently42]

Silly positive and negative: who's responsible for electricity having polarity any way?

Is adding power to the beta22 with out C16 safe, that I might test voltages? I figure that it is, seeing as I think the cap in question has to do with filtering.

 

[Pars]

I would think that would be safe as well. It is only a filter cap on the V- rail and you have C12 in still I assume?

 

[wolf18t]

I don't think firing up without C16 installed will cause more damage.

But there's good chances reverting Gnd and V- could have made some damage on a few places. Now I would plug only 1 board to PS and debug them one at a time using AMB provided operating point PDFs.

 

[Presently42]

I plugged in each board as suggested: all LEDs illuminated and nothing seemed to be awry.

As to the voltages, I believe that I can not take them without two things: Firstly, all parts must be present so that Secondly, the trimpots may be properly adjusted. Or am I wrong.? Does C16 need to be present to adjust the trimpots correctly?

 

[amb]

I suggest that you take the time and install all parts before proceeding.

 

[Presently42]

Hmm. I was hoping that I would be able to make only one order to mouser: were I to order just the dead C16 caps and were there to be more parts needing replacing, I would have to make two orders, which is at least $16 in shipping.

Bit of a catch-22, I suppose.