Where to source replacement parts for QCX mini? #qcxmini #magicsmoke #parts


Ian VA7ITM
 

Having accidently released magic smoke from D2 (note that the AMS1117 voltage regulator is fine) I am looking for some replacement parts. If I assume everything on the 5V line is fried then I need:
FST3253 MUX, SI5351A, 74ACT00, 1N4148 x 2 diodes, ATMega328P processor, LM4562 op-amp and possibly also the LCD. My original reason for fault tracing was low audio output... so I probably also need OPA2277 x 5.

With the exception of the OPA2277, where local prices in Canada make repair uneconomical, I can source most other parts quite inexpensively. The problem is I cannot get them all from the same place... in fact I need to go to 3 separate places. Once each adds on their $10 shipping fee then suddenly again repair is uneconomical.

My last hope was Aliexpress... but again you have to buy from multiple sources and thus multiple shipping charges... though the charges are less.

Of course, the ideal solution would be for QRP Labs to sell these replacement parts so only one shipping charge.

Failing that, has anyone found a common source (or a store in Aliexpress) for all QCX mini replacement parts?

73 Ian VA7ITM


Shirley Dulcey KE1L
 

You should be able to get most of those from Digi-Key or Mouser. You'll have to substitute an SN74CBT3253CDR for the FST3253 but that's a Hans-approved substitution; the supply of FST3253 chips in SOIC has dried up (ON Semiconductor stopped making them a while ago) so future QCX kits will have the TI chip.

NONE of the major distributors have the Si5351A right now; the chip is back-ordered for months. Take your chances on an eBay, Amazon, or AliExpressseller, find a ham who can provide one, or desolder one from an Si5351A breakout board if you have one of those. I don't recommend trying the last method unless you have a hot air rework station.

LCD displays are always crazy expensive from the major distributors. You're better off getting those from specialty dealers or Asian sources. buydisplay.com is one good source. Hans may be able to provide info about where to get a suitable display; you have to make sure to get one with the correct dimensions because the fit in the case is tight.

Good luck!

On Wed, Jan 27, 2021 at 2:31 AM Ian VA7ITM <ian.mcalpine@...> wrote:
Having accidently released magic smoke from D2 (note that the AMS1117 voltage regulator is fine) I am looking for some replacement parts. If I assume everything on the 5V line is fried then I need:
FST3253 MUX, SI5351A, 74ACT00, 1N4148 x 2 diodes, ATMega328P processor, LM4562 op-amp and possibly also the LCD. My original reason for fault tracing was low audio output... so I probably also need OPA2277 x 5.

With the exception of the OPA2277, where local prices in Canada make repair uneconomical, I can source most other parts quite inexpensively. The problem is I cannot get them all from the same place... in fact I need to go to 3 separate places. Once each adds on their $10 shipping fee then suddenly again repair is uneconomical.

My last hope was Aliexpress... but again you have to buy from multiple sources and thus multiple shipping charges... though the charges are less.

Of course, the ideal solution would be for QRP Labs to sell these replacement parts so only one shipping charge.

Failing that, has anyone found a common source (or a store in Aliexpress) for all QCX mini replacement parts?

73 Ian VA7ITM


Alan G4ZFQ
 

Having accidently released magic smoke from D2 (note that the AMS1117 voltage regulator is fine)
Ian,

Then what makes you think you need all those components?

If the regulator is good then none of the 5V parts would be damaged. Did you check the 5 volts?
Look at the schematic D1 and D2 simply feed the Si5351.
You either blew D2 by shorting it to ground or the Si5351 is faulty.
Replace both diodes, see what happens.
Faulty OPA2277 have been known, sometimes simple voltage checks has determined which one. But there are other just as likely reasons for low audio.

Cool, logical diagnosis is required.

73 Alan G4ZFQ


Ted 2E0THH
 

Hi Ian

I have to completely agree with Alan.
If you fault find your way through it you might find that the solution is just one faulty component.
If you have never done fault finding before it is fun and quite easy to learn (beyond Hans' guide, lots on youtube). I see a lot of talk on here about scatter gun approaches,  but the chances are that you might cause more issues with this approach, certainly working with SMT. It is much more satisfying to identify the fault through cool, logical diagnosis as Alan suggests.

For a probe, I use a piece of thin, solid core wire with only the tiniest (0.1mm) of conductor protruding from the insulation. This ensures that the likelihood of accidently shorting 2 pins on an SMD chip with the probe are virtually nil.

73s Ted


Mike
 

A better probe, with more accuracy, is a steel or stainless steel pin, as used
in dressmaking.
Solder a wire to the head. then cover with heatshrink laving a millimetre or
so uninsulated at its point.

On 27 Jan 2021 at 3:38, Ted 2E0THH wrote:

For a probe, I use a piece of thin, solid core wire with only the tiniest
(0.1mm) of conductor protruding from the insulation. This ensures that the
likelihood of accidently shorting 2 pins on an SMD chip with the probe are
virtually nil.

73s Ted


Ian VA7ITM
 

Thank you all very much for the helpful replies.

@Alan @Ted, replacing D1 and D2 is actually the first thing I'm going to do as I can source those from a local store for $1! It was when I started to look at a worst case scenario, and what I might need to replace, that I then realised repair may not be economically viable because of having to pay shipping costs from 3 different suppliers.

But you're right... I may be lucky and may have only destroyed one or two devices. I'll check the various voltages once I replace D1 and D2.

PS the probes for my DVM and DSO150 cheap-o-scope are "pin" probes suitable for SMD work... but some great ideas there on how to make some.

73 Ian


Ian VA7ITM
 

Thank you Shirley for the alternative to the FST3253. I was not aware of that.

73 Ian


MVS Sarma
 

I suppose you can use 2 normal 4007 diodes in place of 4148.
With external swapped soldering 7805 can be managed..

If the 1117 had passed on 12v to other parts , there would be a burm mark on different components surface. 

After that you can start checking for parts that are suspect. Lcd display ciuld be qualified plugging into any other device you may have. .if need be you can use some interconnect pins to overcome male or female connector issues. 

Instead of bulk replacement, little more effort might be worth.

All the best from India

Sarma vu3zmv

On Thu, 28 Jan 2021, 9:50 am Ian VA7ITM, <ian.mcalpine@...> wrote:
Thank you Shirley for the alternative to the FST3253. I was not aware of that.

73 Ian


Ryan Flowers
 

In the US, I have found arrow.com to be quite good.


 

I purchased my replacement parts at Digikey.   I bought a bunch of them.   Somebody goofed and put a 30pf Capacitor (C30) in the kit instead the required 56pf Cap.   Fudge !!!   I just ordered the parts.   I should have actually inventoried the kit too, but... enjoy the fun of kit building.   I also have the original REV1 board and removed the old voltage regulator and installed the new one the 78M05.   It was a slight goat rope, but it's installed now.   That T1 Toroid.  That was interesting. lol.