Yaesu FT480R

[Chris 1155]

Hello Jon,

I started to carry out tests and found that the waveform on TP8 was a sine wave of 2 volt amplitude. The frequency starting at 145.520 is as follows
.520--680 kz
----1--680.4
----2--680.9
----3--681.4
----4--681.9
----5--680.24
----6--680.0
----7--680.0
----8--679.0
----9--679.4
---30--680.0
I then noticed that crystal X03 was loose and discovered a cracked track on the pcb.
I have repaired this but there still is an intermediate fault in the vicinity of X03. I am working on this and will let you know developments. X03 is the crystal associated with Q15.
I have not started on L17 yet.
Chris.

[Jon_G4MDC]

OK Chris - getting close. In the right area.

If you fix any dry joints or track issues found then maybe TP09 will revert to a range around 3.5V without adjustment of L17.

That oscillator has some problem which means it can't tune the full range and that is why it misbehaves.

A bit cross that I advised you to change a blameless divider chip but I would have done that myself if it were mine. Sorry OM!

[Chris 1155]

Pease don't feel responsible for the chip replacement.
I would never have got this far without your advice.
Will report further findings in due course but am otherwise occupied at the moment.
Thanks once again. Remember its only a hobby, but an intriguing one.
Chris.

[Jon_G4MDC]

OK - I just hope you didn't have to pay too much for it.
Here's hoping you can see something tangible wrong around L17 area.
I think you must be very close to finding it now.

[Chris 1155]

Good evening Jon.
I carried out exploratory investigations around the L17 area and resoldered any suspect looking joints etc although there was nothing obvious. This made no difference to the operation of the radio.
I then adjusted L17 for 3.5 volts on TP09 and 'hey presto' the radio is working as it should. I have not tested it on air but the frequency counter indicates that all is OK.
I will try for some reports tomorrow.
I wish to thank you for your assistance and patience as I would never have got this far without your help and knowledge.
I will let you know how I get on with the 'on air' tests.
Thanks once again.
73 Chris G4BYZ

[Jon_G4MDC]

Well done Chris! That is the news we have been waiting for.
Pleased to have got to the bottom of it in the end.



Now you can get on the air and enjoy it and we know what to look for if someone else has one with this issue.

[Jon_G4MDC]

I forgot to add why I think L17 needed adjustment.
Most likely the crystal in the VCXO X03 has aged. These almost always drift LF over time as impurities in the can settle on the quartz plate.

While that was happening the PLL has been driving the tune Voltage higher in order to compensate. For a long while that will go completely unnoticed.
TP09 Voltage will have been rising and probably started to give an error only on the highest PLL step. That will have become more steps the more the crystal aged.

That loop has a very narrow tuning range so it is well worth checking TP09 on any FT480R. They will all be showing their age.
It will be really interesting to hear what David's is doing. He's busy this weekend but maybe we will find out next week.

[Chris 1155]

Interesting observations Jon and thanks for your further thought.
I have had several contacts today, all with favourable reports.
Look forward to hearing from David in due course.
Thank you once again.
Chris G4BYZ