From: HB9DRI, Alex Artieda via time-nuts <time-nuts@lists.febo.com>

 Sent: November 19, 2025 11:52 PM

 To: time-nuts@lists.febo.com <time-nuts@lists.febo.com>

 Cc: HB9DRI, Alex Artieda <hb9dri@bluewin.ch>

 Subject:

 Dear friends,

 I am totally new in this list, looking for a solution to a problem
 with my Lpfrs-01.

 I had this unit second hand, in optical an functional pristine
 condition ,

 take only 3min to lock. All looks good, except I cannot connect to
 the serial port, the device specified TTL Rx and TX in the label, no
 response at all when send M, when is

 connected to a USB / UART converter and I send M the TX line show a

 permanent 3.6vdc and a train of pulses show up in the oscilloscope,
 at

 the same time the DX line is clamp to 1.4vdc and nothing appears,

 suspect the serial interface buffer is damage.I will apprecite some

 advice to repair the unit, I try tl fk d a diagram with no success,

 only few tier down photos, maybe some body can point me where I can

 start looking, maybe a IC to replace.

 Any help is welcome.

 73 de Alex,

 HB9DRI

Alex, The easiest TTL to USB Bridge Chips to use are from FTDI (~25 years with OS driver support and ability to program). FT232R originally, FT232RN newest. [1]https://ftdichip.com/wp-content/uploads/2024/12/DS_FT232RN.pdf FIRST, Determine the Voltage Level (5, 3.3, or 1.8) of the TTL DATA Lines. The Type A USB connector will have 5 V, per standard. I will assume a 5 Volt TTL Data Line. Sparkfun FTDI USB to TTL (5 volt) Cable. It uses the FT232RQ IC [2]https://www.sparkfun.com/ftdi-cable-5v.html Schematic of Cable [3]https://cdn.sparkfun.com/assets/b/2/e/e/5/FTDI_Cable_5V.pdf FTDI FT232RQ Part Page [4]https://ftdichip.com/products/ft232rq/ Now, the FT232RQ has EEPROM. It can be PROGRAMMED ! The Best feature for your LPFRS-10, You can INVERT the TTL Data Lines. Download from the FTDI Utility Page [5]https://ftdichip.com/utilities/ FT_PROG 3.12.70.678 programming utility is available for download, by clicking [6]here. READ to Understand User Guide (You can BRICK Chip with Improper Usage) [7]https://ftdichip.com/wp-content/uploads/2020/07/AN_124_User_Guide_Fo r_FT_PROG.pdf gb == From: HB9DRI, Alex Artieda via time-nuts <time-nuts@lists.febo.com> Sent: November 19, 2025 11:52 PM To: time-nuts@lists.febo.com <time-nuts@lists.febo.com> Cc: HB9DRI, Alex Artieda <hb9dri@bluewin.ch> Subject: Dear friends, I am totally new in this list, looking for a solution to a problem with my Lpfrs-01. I had this unit second hand, in optical an functional pristine condition , take only 3min to lock. All looks good, except I cannot connect to the serial port, the device specified TTL Rx and TX in the label, no response at all when send M, when is connected to a USB / UART converter and I send M the TX line show a permanent 3.6vdc and a train of pulses show up in the oscilloscope, at the same time the DX line is clamp to 1.4vdc and nothing appears, suspect the serial interface buffer is damage.I will apprecite some advice to repair the unit, I try tl fk d a diagram with no success, only few tier down photos, maybe some body can point me where I can start looking, maybe a IC to replace. Any help is welcome. 73 de Alex, HB9DRI References 1. https://ftdichip.com/wp-content/uploads/2024/12/DS_FT232RN.pdf 2. https://www.sparkfun.com/ftdi-cable-5v.html 3. https://cdn.sparkfun.com/assets/b/2/e/e/5/FTDI_Cable_5V.pdf 4. https://ftdichip.com/products/ft232rq/ 5. https://ftdichip.com/utilities/ 6. https://ftdichip.com/wp-content/uploads/2025/07/FT_Prog_v3.12.70.678-Installer.zip 7. https://ftdichip.com/wp-content/uploads/2020/07/AN_124_User_Guide_For_FT_PROG.pdf