Solar Data

Wednesday, June 28, 2006

The Tale Of The Troublesome 290

I am not QRV on 2mtrs at the moment due to other commitments. So I will tell the tale of a recently purchased FT290 MKII. I bought the 290 off Ebay, it was not too expensive at £70, however when it arrived and I hooked it up I found it had very little output, I contacted the seller who told me that they used it on their local repeater which is possible as they live close to it. Upon Inspection the output device 2sc1971 was duff. I did a quick search and found some brand new
devices on, you guessed it (Ebay) they were £6 which I decided was not a dear price. So I purchased one. It duly arrived and I proceeded to fit it, along with a better bias diode as the old device was a 1n4148 glass diode. I fitted a higher current device after reading an article about diode biasing and the common
mistake of using a small current diode which could break down due to high current loading in SSB mode.

Well I tried everything I just could not get any rf out of the device it was removed and metered atleast 5 times! and it checked out fine. I began to suspect that the device I had aquired had probably been mislabeled as it was drawing current but no RF on 144MHz. at this point I started to doubt my
findings and contacted Chris (G1EZJ) a long standing radio friend. He checked out the radio and also came to a conclusion that the transistor was not what it said it was. At this point I thought I would contact Yaesu to see if they could offer a source for the so called obsolete Transistor. I was very Supprised and pleased to get an email back the following day stating that the device was in stock and was £6 plus £4 postage and packing. which was more or less what I paid before. I ordered the device and prayed it was a faulty device I had fitted previously. I decided to take the device down to Chris's and let him fit it. more for my peace of mind and sanity. Lo and Behold Perfect 2.5W output.
So I came to the conclusion that the RARE devices advertised on Ebay were not what they were labelled. next time i will try Yaesu First!.

Inbetween all this Chris had spotted an FL2025 25W add on PA on you guessed it EBAY. So In like flynn I went and won it again it wasnt too dear £37 with postage. Anyway The amplifier had arrived whilst I was awaiting the 2nd 2sc1971 device for the 290.

The pa had not been connected until I knew the 290 was 100%
Upon hooking up the PA guess what? YES youve got it. NO OUTPUT!.

The FL2025 uses a Mitsubishi brick M57727. I took the system back down to Chris's as he has had a lot of experience with brick devices on 23cms.
And he comfirmed that it was indeed duff. However One thing Chris had done in the past was to repair a 23cms brick that he had zapped.
He removed the plastic cover of the device and metered the different stages and discovered a burnt out bias diode. Now my eyesight is nowhere near good enuff
to start repairing bias circuits on the modules but Chris was in his element, he removed the duff diode metered the device which then checked out fine. So he added a small diode and hooked it all up and 15W output and then with a tweak 25W I was well chuffed and impressed as I did not fancy paying out more money on a new brick.

Thanks Chris!
Since then I have managed to aquire a service manual and the next stage to to get it onto frequency as it is slightly off.
I guess Ebay is basically the same as the old bring and buy at radio rallies where you get the item home and it doesnt work.

Anyway there is the Story. My next project it to build a DK7ZB yagi for 2mtrs
and a mast head preamp. So watch this space and Ill update when I can.
Thanks for reading. Mark

1 comment:

Ian G0UWK said...

Hello Mark,
Have you built your antenna yet?