[IRCA] Dissecting the Grundig S350DL (Tecsun 3000)

[Tim Hills <thills@xxxxxxxxxxxxx>]

I got this radio at a pawn shop for $35 a while back and while it's not 
the ideal DX box for SWL, my primary interest, it does do a very nice 
job on MW after an alignment and a bit of tweaking. I've had it apart 
and back together 4 times now, lacking a service manual or even a 
schematic I'm proceeding cautiously. I've seen some claims that this 
isn't a rebadged Tecsun but all the boards have "Tecsun PL-3000" 
screened on them, you decide. I try to keep in mind that it is a sub 
$100 receiver after all.

I have semi locals during the day on 570 and 1490 that I used to align 
it. The main problem on MW and the strongest plus is the "dual coil" 
internal ferrite rod. The tuning on the rod would not line up with the 
L.O. I haven't investigated if it's a padding cap out of spec, material 
defect in the rod itself or just poor engineering. My guess is on the 
crowded RF board it would have cost too much to add a couple of 
components :( The dual coil is a balanced design similar to what I've 
been using for about 25 years and the problem with my unit was that it 
was not very balanced. One side was about 80KHz higher than the tuned 
Freq. at 1520. The problem was solved with a 20pF trimmer cap 
tack-soldered onto the back of the RF board and sliding the right hand 
coil inwards..

Since the coil is not more adjustable without adding or removing 
windings I had to peak the L.O. to the antenna coil. An S-meter was 
added through a pot from the AGC pin on the display unit. Varying the 
inductor of the MW L.O. and retuning to 570, noting the S-meter readings 
gave me the low end, doing the same at 1520 with the L.O. variable cap 
then repeating the process until there's no improvement to be made for 
alignment then setting the added trim cap for highest signal on 1490 
made a huge improvement in sensitivity and selectivity across the entire 
band. MW tuning now ranges from 505 to 1723 KHz rather than 519 to 1740 
when I got it.

1320 and 1140 used to pop up all over the place but now even those 
ghosts have been exorcised :D

I put AAs in it and went to a quiet hill north of town earlier. Had 
paper but forget to bring a pen or pencil but it was snowing and cold 
out anyway our Kia van has some weird noise generator even with the key 
off so I had to go out and away from it :(  I did a quick spin through 
the band and was getting something on nearly every 10Khz with quite a 
few multiples. Nulling is excellent! I was on a side lobe of 1320 (5KW) 
and while I couldn't completely null it. I was able to get a weak 
carrier on 1310.

I've heard very good and very bad things about the S350DL/Tecsun 3000 
and I think there are good ones and bad ones. I suspect that substandard 
or out of spec parts were put into a lot of them and factory QA is not 
the best

 I have made some other modifications mostly to improve SW reception. 
The S-meter, adding an F connector with a 4:1 un-un for external antenna 
input that bypasses the rod antenna and LP filter entirely and using the 
LP switch to switch from external to built in rod for SW and an 
alignment. There are other problems that I could fix given time, 
incentive and beer. The wide filter seems to be centered about 2KHz 
above the narrow and some that are inherent to the design, images and 
birdies from the display mostly. At this point I consider any further 
attempts at improving it on SW as putting lipstick on a pig

All I can say about the FM reception is that it works since I rarely use 
FM and wouldn't miss it if it wasn't there.

I was going to scrap it and harvest the ferrite rod, display and ICs but 
for now at least it's the best MW portable I've ever owned and since I'm 
still waiting on parts for upgrading my homebrew it's my primary 
receiver for the time being.

Tim Hills
Sioux Falls, SD

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