ct 4839 problem with my ft990

Hi guys 
           I have a yaesu ft 990 rig and its come from a very good friends grand father who has passed away. he has owned it from new and its always worked well. Until now, the problem i have it after using it for maybe 30 mins on usb it goes off frequency and the cooling fan comes in but very slow. i have removed the fan and tested it using a psu and it runs fine but while in the radio its very slow. I have the full radio diagrams for reference can anyone suggest or recommend a good rig doctor that could help? 
any help would be gratefully accepted

best regards Terry

Hi Terry,

Just a quick couple of questions that may alleviate some headaches to start with :-

How do you know that you are off frequency?
Is someone telling you that your USB 'sounds' off frequency or are they reading off their dial and exclaiming as much. How does your other modes of transmission perform, (i.e. does the same problem occur on LSB as well?)

Have you confirmed your own frequency either with a frequency counter (on a constant carrier mode such as CW, AM or FM) or otherwise reception from a standardised beacon or transmission? (For example the 'Shannon Volmet' transmission at 5.505MHz USB.)

As for your fan 'test' the fan is controlled by a thermistor and op-amp circuit on the P.A. (power amplifier) board and won't be flat out unless the P.A. is running very hot. So running slowly within the radio itself would be perfectly normal and will obviously spin flat out with your simple test of hooking it to an external supply.

There are some common faults with the FT990 (the pesky 5 volt regulator's solder joints for one!) but on the whole it's generally found to be a good performing rig.

Always worth reassuring yourself of any so called 'reported' faults before jumping the gun.

As for "rig doctor's" it can all be a bit of a mine-field but I know I would personally have a repair or service/alignment performed by an authorised Yaesu repair centre.


I hope you get sorted to your own satisfaction but just be aware of typical third hand comments of "Yeah, needs re-capping mate" and the like. I don't believe anyone says this sort of stuff out of malice, but a 'little' knowledge can be a dangerous thing.

All the best,
Victor

Hi Victor,

Thank you for your reply,
I have not tested it using any kind of testing equipment how ever i am only
back to the hobby a short time and do not have the experience yet to know
what tester or meters i would require.
Because I have only just started to get into the hobby i spend most of my 
time listening and picking up the radio etiquette and abbreviations however
on a Saturday Nights i have spent time at 27.585 usb CT net chat and it here
i found the problem i am having,,,,
while talking with Maxine and John i noticed my reception was changing from
nice and clear to very darlic like and at times they sounded to be on maybe FM 
not usb . They to reported that i sounded to be off frequency along with others
in the group. If i stop modulating after maybe 15 / 20 mins my reception returns to normal.

its all very strange to me , i have even had rig checks from my very good friend that gave me 
rig and he too told me after a while chatting my signal drifts in and out.

thank you for your advice

best regards Terry

Hi Tony,

Really sorry to hear of the problems as it does obviously sound like it needs a repair but at least you've verified that as best as you're able. I would suspect a P.A. and/or regulator board problem so any technician worth their salt should be able to repair it. The only matter after that is how much is it going to cost to repair so it may be worth telephoning as many places as you can to get an idea on price. 

Apologies for not being able to help you out further and I hope you get it all sorted out.

All my very best to you and good luck,
Victor

Hi Victor

            Thank you for your help at least I have a starting point with a board you think maybe at
fault. I will indeed ring as many radio shops as possible to obtain a realistic quote for the repair, 
i have also emailed yaesu uk as they do repairs too ( bet they will not be cheap ) .


thank you for your input its gratefully received.

all the best regards Terry