Re: FT 290 problem


Mansueto Grech <mansueto.grech@...>
 

Hi Coin,
Don't give up on the rig.
Writing it off is not the solution.
73's

Mans. 9H1GB

On Nov 15, 2011 5:18 PM, "M5FRA - Colin" <m5fra@...> wrote:
 

Bill, a very big thank you for the most coherent explanation of the
likely probelm. I have changed a few 10mfd electrolytics already, some
were visibly leaking others had a v.high ESR. Will have another look
before I write it off.

Colin - G8FRA/M5FRA

www.m5fra.org.uk

------ Original Message ------
From: "Bill Hall" <whhall@...>
To: ukmicrowaves@...
Sent: 15/11/2011 15:42:49
Subject: [ukmicrowaves] Re: FT 290 problem
>Colin, here is more info for you.
>If there is no negative 6.8 volt supply then Q1014 cannot take the gate of Q1015 negative and so it cannot be pinched off. This means that the S meter will always read full scale. The TX ALC problem is the same mechanism. The -6.8 volts is generated by Q4005 ICL7660 on the regulator board. This has probably stopped working because C4014 or C4015 have gone leaky. The extra current drawn is killing the DC-DC convertor. After a while the capacitor reforms enough to reduce the leakage and the convertor will recover and start working again. I would replace both capacitors if you confirm that this is the problem.
>
>I hope this explanation helps.
>
>bill G3RMX
>
>--- In ukmicrowaves@..., "colin" wrote:
>
>>
>>
>>My Mk1 290 has developed a fault - on switch on the S meter goes hard over and the TX will not work. After a period of time, depending on how long the radio was last used, the S meter gradually returns to zero and the TX O/P rises.
>>
>>This is a common fault and the only cure I have seen is to remove Q1014 which kills the AGC. Not a good fix.
>>
>>Has anybody any ideas on a proper repair?
>>
>>Colin - G8FRA/M5FRA
>>
>>
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