I need help with a DX 200 (realistic)

[kg4dmc]

I normally work on tube gear and am out of my element on this one:
I picked up a DX 200 with distorted audio. I believe that I have narrowed the problem down to the AGC. SSB reception and audio are good (with the AGC on Fast, of course). The AM audio distorts more on strong signal than weak and actually improves when switched to Fast. I noticed that VR 201 was turned almost all of the way to the right, but if I attempted to turn it in either direction, the audio got worse.
The only fron panel control that I could turn to improve the audio was the RF Gain. By decreasing the signal strength to less than 5, I was able to get audio that was almost free of distortion.
Where do I go from here? There is no obvious damage to any component. I have the schematic, but I would hate to just start replacing each of the components in the AGC one by one until I found the problem.

[K9YLI]

dig out your silly scope and check the power supply voltages while haveing strong audio.
watch for voltage variations and ripple..

I just bought 49 NIB 2 or 3 sections electrolytics for 5 bucks at an auction..

whoo hoo..
second check withthe scope at the center pin of the audio control.
distortion is either before or after that.

which is to say, in the detector or the audio section.

the more you learn about it the more you can eliminate.

[K5RCD]

I normally work on tube gear and am out of my element on this one:
I picked up a DX 200 with distorted audio. I believe that I have narrowed the problem down to the AGC. SSB reception and audio are good (with the AGC on Fast, of course). The AM audio distorts more on strong signal than weak and actually improves when switched to Fast. I noticed that VR 201 was turned almost all of the way to the right, but if I attempted to turn it in either direction, the audio got worse.
The only fron panel control that I could turn to improve the audio was the RF Gain. By decreasing the signal strength to less than 5, I was able to get audio that was almost free of distortion.
Where do I go from here? There is no obvious damage to any component. I have the schematic, but I would hate to just start replacing each of the components in the AGC one by one until I found the problem.

I bought one used (for shortwave broadcast listening) at a hamfest a couple years ago and it had the same exact problem.
I opened it up and sprayed a liberal dose of tuner cleaner into it, especially into the back of each of the control knobs while turning them. After letting it dry thoroughly the problem cleared up.
It's worth a try.

[kg4dmc]

I tried the tuner wash, no luck. I'm not high tech enough to have a scope. Looked at just trying to replace the AGC transistor, as all of the diodes check ok. Can't find anyone that carries the transistor (2SC1815)!
Thanks for trying to help out fellows. Anyone want to buy a DX 200!

[kc4umo]

I had one of these years ago.
Several problems I seen was distorted audio, hissing audio, very low audio.
Each time is was the same component causing the problem. In the front end of the receiver is a dual-gate MOSFET. I can not remember the part number. Problem is the part takes a lot of static from the antenna and gets damaged.

Go to AM mode and use a long piece of insulated wire with 1/8 of the insulation removed (acts like a probe and antenna) touch the base of the transistor that is following the MOSFET. If audio is weak but clear, the MOSFET is bad.