Hi Ron many thanks for the helpful and welcome info and advice. I'd been working on the assumption that there's a problem somewhere around IC6 and IC7 stages/ circuitry on account of not being able to

#calibration #opamp #20m

Hi I just wanted to post the results of my qcx-mini. I posted earlier in this thread that I had the same symptons as Josh and had recorded the voltages on all pins from IC6-IC10. The voltages on IC10

#20m #alignment #qcxmini

Hi Rod. If you’re getting that good of a signal level on the BPF adjustment then you have audio through IC5,6&7. It’s disappearing somewhere through IC8,9 or 10 for some reason. Since you don’t have a

#calibration #opamp #20m

Hi I'm another with this opportunity (I just hope it isn't insurmountable!). All voltages seem ok, I've checked T1, any number of soldered connections - no joy (and no dual sweep 'scope). The BPF peak

#calibration #opamp #20m

I'm having the same problem and all the voltages check out. I'm going to try some other trouble shooting steps this weekend and see if I can't get it going.

#calibration #opamp #20m

I am experiencing similar issues: everything works and sounds like a radio, but it is mostly deaf, and there is no effect from the alignment pots. Established continuity and correct component values t

#calibration #opamp #20m

Where were you looking? it's available at this link for $3.00 ea. https://www.ebay.com/itm/3B3253-High-Bandwidth-4-1-Mux-DeMu-IC-16pin-TSSOP-QTY-1/330550179839?hash=item4cf65377ff:g:168AAOxyvSVREogY

#20m #troubleshooting #help

Yes I have used that ebay store to purchase small quantities before. Had no problems with delivery or anything, but that was more than a year ago. Perhaps they are temporarily out of stock?

#20m #troubleshooting #help

There is an "IBS electronics" that seems to sell them but it also looks like a dead end. Probably you need to order a full reel or more.

#20m #troubleshooting #help

Interesting specs. However, the only sales agency I could find was an Ebay store listed on Potato's website, but comes up as "0 results" when searched for on Ebay. 73 Jim W4JED

#20m #troubleshooting #help

Yes you would have to tack some diodes in the supply line to the potato chip but it might improve the performance of the QCX at the upper end. Potato semi make a bunch of nice real high speed variants

#20m #troubleshooting #help

Thanks, Fred. Ok on the two different TI part numbers for 5v vs. 3.3v. I had to look up the Potato Chip company as I was curious who they were. They are ‘fabless’ meaning they have to contract other s

#20m #troubleshooting #help

For the TI part, you would want the SN74CBT3253CD(R) for the SOIC 5V (7V max) version not the LV version. Mouser qty 1: $0.70 (US) QS3253S1G8: $0.55 Digi-Key qty 1: $0.70 QS3253S1G8: $0.68 Those are t

#20m #troubleshooting #help

I see from the PO3B3253A and 74CBTLV3253D datasheets these are Vcc 3.3v devices and the current schematic has IC4 at Vcc +5v. So they wouldn't be drop in replacements unless Vcc is changed on IC4 or I

#20m #troubleshooting #help

Another option is the one made by potato semi. Maybe a better choice if you are building for the higher frequency bands http://www.potatosemi.com/potatosemiweb/datasheet/PO3B3253A.pdf

#20m #troubleshooting #help

Note that all QRP Labs products (incl QCX+ and QVC-mini) will use the SOIC16 TI part going forward since even our substantial stock of FST parts is gone. 73 Hans G0UPL http://qrp-labs.com

#20m #troubleshooting #help

When I eventually get a Mouser or Digi-Key order in I plan on buying a few QS3253S1G8 parts because they are the closest electrically and mechanically to the current discontinued FST3253MX SOIC parts.

#20m #troubleshooting #help

Sorry Vince Not even close. The 138 is a single 3 to 8 decoder. The 3253 is a dual 1 to 4 decoder. You replace a 3253 with another 3253. 73 Jim W4JED

#20m #troubleshooting #help

Vince, the 74HC138 is a 3-to-8 Line Decoder/Demultiplexer. The FST 3253 is a 4:1 multiplexer / demultiplexer. So I guess the answer is NO. It is not a good substitute. Ron

#20m #troubleshooting #help

Quick question can i substitute a CD74HC138 for the FST 3253?? asking for a friend who has the 74HC138.. Vince

#20m #troubleshooting #help