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KF5AIE
03-07-2016, 08:04 AM
My Alinco DX-77t transmits distorted on 40M in high power selection, SSB, CW, or any Mode. In low power all is well. I have tried all antennae and dummy load. I even checked coax-both to antenna and jumpers. It also distorts on other bands as well but 40M is the worst. Before a neighborhood lightning strike the DX-77t was great. Not good but great! D607 was leaky and was replaced. I shall not send the radio back to S.D. for any more expensive repair. Are there any suggestions as what to do about that RFI type distortion? '73 KF5AIE

AD0X
04-01-2016, 08:38 AM
Hi Robert,

Did you make any progress with your rig diagnosis?
I am reviewing the service manual now.

73's,
Joe, AD0X

KF5AIE
04-10-2016, 02:57 PM
Joe, I sent it back to Burkhart Radio Repair in South Dakota. Last I heard from them it was working OK. Still do not know why I am distorting so much on 40M. We suspected Power Supply voltage, but it seems within specs. I might have to live with low power from now on if I keep the Alinco DX-77t. It was such a great little radio. I miss it plenty. TNX, KF5AIE robert

AD0X
04-11-2016, 06:18 PM
Robert,

One possible effect would be power supply droop under load. The would only occur on high power. The push-pull final amplifier would need an RF voltmeter (or other equipment) to check for final asymmetry) to account for the waveform distortion.

If Burkhart says it is working OK now, the first possibility above is likely. I would ask them how it was tested so you have a reference point in the future.

The final device bias can also be an issue and I note that the metering is not isolated to the device, but the combination so trouble shooting is difficult.

One idea would be to take an IR/temperature scan when it is working, under a dummy load, and using that as a reference to point to components that stop working at a later time.

73's,
Joe
AD0X


Joe, I sent it back to Burkhart Radio Repair in South Dakota. Last I heard from them it was working OK. Still do not know why I am distorting so much on 40M. We suspected Power Supply voltage, but it seems within specs. I might have to live with low power from now on if I keep the Alinco DX-77t. It was such a great little radio. I miss it plenty. TNX, KF5AIE robert

KF5AIE
04-12-2016, 07:07 AM
Joe, When the Alinco DX-77t is returned I shall try it out with a borrowed power supply to eliminate possible power supply problem. Both parties are using Astron RS-35Ms. All I have to test things with is a an old trusty Fluke Model 8020B multimeter. I so think you have the answer concerning a distorted or messy DC component. Changing power supplies is next scheduled test here in the shack.
TNX, and mucho '73, KF5AIE Robert