Realistic DX-302 Troubleshooting

[Dominic1967]

I swear this radio was messed up before I touched it.

I found another DX-302 for a song on eBay. It was described as deaf but when I got it, I could absolutely receive some strong stations. And the MHz gear was perfect. I was pretty happy about that.

Initially, receive was weak and the audio was very scratchy. Deoxit helped things some. Then I replaced 12 caps, replaced the speaker and swapped out the entire attenuator board from donor parts (the selectivity switch was broken.) It still isn't right and I'm not sure where next to turn for troubleshooting.

Now that i've replaced the caps in the audio section, I get quite a bit of low end when "AM" is chosen but lose all the bass when switched to "AM ANL." Not sure if that's normal. My "good" one does that too and the caps in its audio section were replaced as well. Is that a "symptom" of performing W4JBM's audio mod?

My big issue is the "pumping" of strong signals and the lack of movement from the signal meter when strong signals are present. In fact, the needle moves very little at all. Reception seems to fade in and out far more than it should. An A/B comparison with the "good" DX-302 proves that. At times the radio is overloading and at others, I have to turn up the volume. Lastly, single sideband is only intelligible when the BFO knob is set to one extreme.

I love a challenge and I have some handy tools, but my skill set is not that strong. I'm above the beginner level but lacking in many electronics troubleshooting skills. Most of what I know has come from watching Youtube videos and learning from my own mistakes. With these symptoms, should I be focusing my attention in one area more than another? I haven't touched the RF board, except to clip R227, which mutes the MHz dial when tuning. I did that on both radios.

I appreciate any advice you can give.

Thanks,
Dominic

 

[Blackswan73]

Lack of S meter movement could indicate a problem in the RF amplifier section, possibly the RF amplifier transistor. Replacements can be found on EBay. You can download a service manual to locate the amplifier transistor.

B.S.

 

[Dominic1967]

Lack of S meter movement could indicate a problem in the RF amplifier section, possibly the RF amplifier transistor. Replacements can be found on EBay. You can download a service manual to locate the amplifier transistor.

B.S.

Got it. Thanks.
So the RF amp transistor is Q201. I can measure the voltage and see if it corresponds to what the service manual specifies. I wasn't sure if this was an AGC thing or RF amp-related. I do wish the service manual copies that can be found online had been scanned a little better.

Thanks,
Dominic

 

[Dominic1967]

Here's another question regarding this model that I posted in another group;

I know printed circuit boards can go through changes before production is finalized but I'm curious about one change in particular in the DX-302.
A capacitor labelled C330 has been slightly moved- the board shows where it was intended to go, along with polarity placement, but it's actually been stretched to tie into another point on the board. I'd really like to know why the change was made. The service manual shows the change. C330 is a 10 mF 16V capacitor, which is backed up in the manual. Does anyone know why this change was made?













Thanks,
Dominic

 

[BabaYaga60]

Here's another question regarding this model that I posted in another group;

I know printed circuit boards can go through changes before production is finalized but I'm curious about one change in particular in the DX-302.
A capacitor labelled C330 has been slightly moved- the board shows where it was intended to go, along with polarity placement, but it's actually been stretched to tie into another point on the board. I'd really like to know why the change was made. The service manual shows the change. C330 is a 10 mF 16V capacitor, which is backed up in the manual. Does anyone know why this change was made?


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Thanks,
Dominic

Great pictures, BTW ! The days of thru hole boards *Sigh*

 

[Dominic1967]

So, about the audio mod that has been floating around the internet for a few years- W4JBM suggests replacing 7 caps in the audio section, changing all of their values. Terry at D-Lab has a video on the whole mod, including upgrading the speaker (probably the most important step.) Of all the caps, the two that seem to make the most difference are C378 and C379, both 100 μF electrolytics that he suggests upping to 330 or greater. Terry uses 470, so that's what I used, as well. Man, talk about low end- the mod takes away the tinny, anemic sound and replaces it with quite a booming, fuller one. Maybe too much...? I have some 330 μF caps coming which I'll swap out to maybe tame that low end a bit.

At any rate, before I did this, switching from AM to AM/ANL made no difference that my ears could detect. After the mod? Night and day. The AM selection is bassy and boomy (those are terms, right?) and AM/ANL is back to tinny and weak. So that begs the question, does the AM/ANL circuit path bypass some of the audio section, thus cutting out the mod?

At first I thought I had done something wrong, but it's the same on both of my modded DX-302s and there is no difference on my latest, unmolested unit. (I got one today that had a sticker from the Radio Shack repair center and it's maybe the best one I've owned yet. Single sideband hardly needs adjusting.) Just wondering if anyone had any experience with audio issues or that AM/ANL feature.

Thanks,
Dominic