FT290 mk1 o/p power - UK Vintage Radio Repair and Restoration Discussion Forum

Mikegallon · 10th Dec 2015, 9:28 pm

Hi,
I have an ft290 mk1 that has a power o/p fault. The o/p transistor is fine as is the driver. The set only gives .5w in the high power setting and 0 in low power. I think the fault is in the alc circuit. Has anyone come across this fault please.
Thank you
Mike

Aub · 11th Dec 2015, 12:23 pm

Is the power switching circuitry working? i would think that 0.5w is about right for the low power setting. Isn't alc a receiver attribute?

Hope you get it sorted.

Cheers

Aub

Jon_G4MDC · 11th Dec 2015, 5:41 pm

Don't know much about FT290 of any model but apart from ALC (which is correct in TX parlance c/w AGC for RX side) this could also be down to problems in T/R Antenna switch or low pass filter which follows? Not sure if relay or PIN diode type in one of those.

What is current drawn on TX compared to normal spec could also be a clue?

SiriusHardware · 12th Dec 2015, 8:39 pm

Quote:

Originally Posted by Aub

Is the power switching circuitry working? i would think that 0.5w is about right for the low power setting. Isn't alc a receiver attribute?

The FT290 has SSB as one of its modes so ALC in this context could refer to the ALC of the RF amplifier, which is linear (rather than class C as it might be in a non-SSB transmitter). Or it could refer to the ALC of the microphone audio amplifier stage.

Mikegallon: My FT290R2 has FM, and I assume the original FT290 does as well. Are these power problems present across all modes, or only on SSB?

Mikegallon · 12th Dec 2015, 9:04 pm

Thank you for the replies,
The set gives 1/2w in hi position and 0 in the low power position. The 6.8v is present for the t/r switching. The manual gives no indication as to what to expect as alc voltages only 6.8 should be present in the low power setting. The fault came on suddenly so somethings popped. Thanks for the tip, I'll check the switching diodes next. Sorry I should have said the set has fm and the fault is across all modes.

Mikegallon · 14th Dec 2015, 7:13 pm

Bingo!
I've got the high power back,but the low power is still a problem. The high power problem was a dirty function switch. The low power now gives 20's,brought up by the high power restoration. The remaining problem is, I think is associated with either the mosfet buffer or the low power switching transistor. More time needed now and I think this one is going to be tricky.
Mike

Jon_G4MDC · 16th Dec 2015, 6:35 pm

Good news about that Mike.
Not sure what power you have on low setting now? It seems a slight typo crept in to your last post just there. Is it 200mW?

I see from manual High spec o/p is 2.5W so 200mW is 11dB down if you actually get 2.5W on high.
The spec says 0.5W for low power so 7dB down is normal.

There is a pot for setting low power VR2006. Maybe a previous owner had a linear amp that needed only 0.2W drive and set low power to suit?

Looking down on the main board with the dial at front. The pot is to the left of the bottom left corner of the crystal filter. Hopefully the board has component ID printed by silk screen?

Mikegallon · 17th Dec 2015, 9:25 pm

Thank you Jon,
The low power is 20mw only. I'm looking again at the 2SC2603 switching transistor and associated components. The pot you mention is fine, I've had that out to test it. That leaves the base bias and collector resistors plus 1disc capacitor. The transistor measures ok on the board but it could still be faulty. I'm waiting for desolder wick to arrive to lift the device and I've found an equivalent for it (BC547). So that's it up to now. Many thanks for the tips Jon.
Mike

10th Dec 2015, 9:28 pm	#1
Mikegallon Retired Dormant Member Join Date: Dec 2015 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 4	FT290 mk1 o/p power Hi, I have an ft290 mk1 that has a power o/p fault. The o/p transistor is fine as is the driver. The set only gives .5w in the high power setting and 0 in low power. I think the fault is in the alc circuit. Has anyone come across this fault please. Thank you Mike

11th Dec 2015, 12:23 pm	#2
Aub Nonode Join Date: Mar 2005 Location: Nuneaton, Warwickshire, UK. Posts: 2,039	Re: FT290 mk1 o/p power Is the power switching circuitry working? i would think that 0.5w is about right for the low power setting. Isn't alc a receiver attribute? Hope you get it sorted. Cheers Aub __________________ Life's a long song, but the tune ends too soon for us all.

11th Dec 2015, 5:41 pm	#3
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: FT290 mk1 o/p power Don't know much about FT290 of any model but apart from ALC (which is correct in TX parlance c/w AGC for RX side) this could also be down to problems in T/R Antenna switch or low pass filter which follows? Not sure if relay or PIN diode type in one of those. What is current drawn on TX compared to normal spec could also be a clue?

12th Dec 2015, 9:04 pm	#5
Mikegallon Retired Dormant Member Join Date: Dec 2015 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 4	Re: FT290 mk1 o/p power Thank you for the replies, The set gives 1/2w in hi position and 0 in the low power position. The 6.8v is present for the t/r switching. The manual gives no indication as to what to expect as alc voltages only 6.8 should be present in the low power setting. The fault came on suddenly so somethings popped. Thanks for the tip, I'll check the switching diodes next. Sorry I should have said the set has fm and the fault is across all modes.

14th Dec 2015, 7:13 pm	#6
Mikegallon Retired Dormant Member Join Date: Dec 2015 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 4	Re: FT290 mk1 o/p power Bingo! I've got the high power back,but the low power is still a problem. The high power problem was a dirty function switch. The low power now gives 20's,brought up by the high power restoration. The remaining problem is, I think is associated with either the mosfet buffer or the low power switching transistor. More time needed now and I think this one is going to be tricky. Mike

16th Dec 2015, 6:35 pm	#7
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: FT290 mk1 o/p power Good news about that Mike. Not sure what power you have on low setting now? It seems a slight typo crept in to your last post just there. Is it 200mW? I see from manual High spec o/p is 2.5W so 200mW is 11dB down if you actually get 2.5W on high. The spec says 0.5W for low power so 7dB down is normal. There is a pot for setting low power VR2006. Maybe a previous owner had a linear amp that needed only 0.2W drive and set low power to suit? Looking down on the main board with the dial at front. The pot is to the left of the bottom left corner of the crystal filter. Hopefully the board has component ID printed by silk screen?

17th Dec 2015, 9:25 pm	#8
Mikegallon Retired Dormant Member Join Date: Dec 2015 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 4	Re: FT290 mk1 o/p power Thank you Jon, The low power is 20mw only. I'm looking again at the 2SC2603 switching transistor and associated components. The pot you mention is fine, I've had that out to test it. That leaves the base bias and collector resistors plus 1disc capacitor. The transistor measures ok on the board but it could still be faulty. I'm waiting for desolder wick to arrive to lift the device and I've found an equivalent for it (BC547). So that's it up to now. Many thanks for the tips Jon. Mike