Re: Request for QMX troubleshooting guidance
|
Lloyd, "I should have noted that Tx is not shorted to ground (a little over 100K)"
- OK? that looks good!
"Per your suggestion I verified continuity between the MPU Tx pin and one of the 7408's Tx inputs. That is also good."
Yes, agreed!
"Maybe the end of the road. Unless, since RF is only present at the 7408 on key-down, could the gating inputs be jury-rigged to 3.3v ¡ªjust a thought."
Now that is a puzzle! What you describe here does not sound correct to me. The TX line, as I understand it, should be what conveys the key-down/key-up modulation to the PA, not via CLK2.?
You might perform a factory reset and repeat the test. A reload of the FW and a factory reset might be next. Finally, you might choose to send your unit to Jeff Moore for diagnosis and repair. If the problem is other than a damaged MCU or a PC board defect, he stands a very good chance of being able to find and fix it. I would not recommend the mod you proposed due to potential unintended (possibly 'blue smoke') consequences.
JZ
?
On Mon, Feb 5, 2024, 7:45?AM Lloyd Milligan < himself@...> wrote: Thanks John. ? I should have noted that Tx is not shorted to ground (a little over 100K). ? Per your suggestion I verified continuity between the MPU Tx pin and one of the 7408's Tx inputs. That is also good. ? Maybe the end of the road. Unless, since RF is only present at the 7408 on key-down, could the gating inputs be jury-rigged to 3.3v ¡ªjust a thought. ? -Lloyd (wa4efs) ? From: [email protected] [mailto:[email protected]] On Behalf Of John Z
Sent: Saturday, February 3, 2024 5:42 PM
To: [email protected]
Subject: Re: [QRPLabs] Request for QMX troubleshooting guidance ? Lloyd, With power off, check the resistance from TX to ground. Is it low/shorted? Check for continuity from the MCU TX pin to the '08 TX inputs. Is the solder joint at the MCU pin good? ? On Sat, Feb 3, 2024, 3:35?PM Lloyd Milligan <himself@...> wrote: Hello, ? I have just completed assembly of the 20-to-10 meter QMX. Controls and inputs are good (firmware 1_00_014). Receive works very well¡ªgreat sensitivity. However, no RF output on any band. ? On key-down, CLK2 makes it through the XORs but not through the 7408. The latter¡¯s Tx inputs (2, 3, 10, 13) do not change state on key-down (The IC has power and the CLK2 inputs have signal). Thus there is no RF input to the BS170s. I would be grateful for a suggestion as to where to check next. ? Thank you, Lloyd (wa4efs)
|
