Tecsun PL-600 teardown / ssb audio mod (pic heavy)

SWLing and TX Forum, for everything below 30MHz...

Tecsun PL-600 teardown / ssb audio mod (pic heavy)

Postby radiostationx » Sat Jul 21, 2018 11:39 pm

Tecsun PL-600 SW Radio Improvements to SSB audio modification.

The Tecsun PL-600 is a great radio for the cash, some time ago I gave a thumbs up for it on this forum.

http://derbosoft.proboards.com/thread/1 ... er-airband

A real bargain for the price.

Image


I decided to complete a modification to the am audio circuit to improve ssb reception as sometimes especially with strong stations, the PL-600 can get overloaded with the intended signal and poor quality audio from the speaker is the result.

There are some writeups on the internet for the mod "insert 1k resistor into audio IC at pin 18 and ground".
Thats about it.. and a few youtube vids on the resulting audio but Not much at all in the way of a guide as to how to take the radio apart or complete the job. Very vague indeed.

There was much talk on internet boards regarding this mod, but just that.. talk .
Lets not talk.. lets do ! :happy:

Oh well, nothing ventured..so here goes,He who dares..
Lets get in there and see the gubbins.

Put the radio face down on a jiffy bag to protect the front from scratches.

Image

Open the radio by removing the 4 pointed scews marked A , next the 2 blunt screws from inside the battery chamber marked B. Finally pull off the 3 knobs at the side marked C.
The front bezel of the radio will now come free along with the lanyard carrying string.

Image

The speaker is attached to the front on a short pair of wires so you have to manipulate the front to get it out of the way without detatching them.The front removed you can see partly through to the main pll/logic board. The keypad pcb is attached piggy back style to it. The area we want is covered by the LCD display.


Image

Now remove both circuit board assemblies as one unit by levering up on one corner and gradually coax the whole lot up and out of the casing. Jockey it slightly as you lift up and out.

Image

Next , the audio IC sits inside the main PLL/Logic pcb. This is joined piggy back onto the keypad pcb. Now you have 2 choices,

1. get at the audio IC component side by removing the keypad/LCD pcb and soldering a resisitor on the audio chip itself from the front of the logic/pll board (I spotted a post in russian of a user who did this, it is not easy as the ground point he used was a metal shield, through the meduim of google translate I noted he had extreme difficulty getting the keypad pcb back to its home location without damaging the new resistor junction he had just made).
I removed the keypad/lcd pcb, had a little look in there and immediately felt his pain. The access seems fine when the 2 boards are apart but only a wafer thin gap exists when they are back together.
I made some notes and shut up shop again.

2 . Do the joint on the solder side of the main logic/pcb. My choice.

No contest, option 2 it is.

Flip over the board to the solder side, the item we need is the audio IC . It is a 24 pin package. When i took a peep inside the 2 boards earlier, I noted the orientation of the IC (where pin 1 is located) I marked it with a sharpie on the solder side for reference.
The chip is a Toshiba TA2057N.

Image

Pin 18 is the AM out ..and handy enough pin 8 is ground.
Solder a 1k resistor between these 2 pins on the solder side. This area is quite small, take your time with a low wattage iron.
Image

A word on the solder, it seems to be eco friendly rubbish or poor solder with low lead content used throughout the radio. Difficult to work with.


Check value when you are done . Use small croc clips for this job, too small an area for meter probes. I marked pin 1 from when I took a quick look at the other side earlier on.

Image

My fab Chauvin Arnoux Metrix MX-26 multimeter is dead on the money,it should be, so expensive when I bought it ! Calibrated annually.

Meter says good 0.996 k ohms,thats close enough !

Image



Cover adjacent board pins with tape then carefully bend the resistor down flat on top of the pvc tape cushion making sure that the junction does not come apart.

Image

Check with magnifier and minature podger (thick needle) to make sure all is well with the joints and they are not loose or dry.

While you are here, replace the 2 speaker wires (these are poor quality) with decent thicker copper ones.
This will also improve the audio from the loudspeaker.
Solder locations are marked on the board ,SP1 and SP2.

Image

You are limited in wire choices here by the hole size in the pcb but , with patience, you can get 3 times thicker wires in there than the originals. Keep the length the same even though this is a pain. The last thing you need is a pair of wires in the display window when you are all boxed up !
Swap out the FM antenna wire link with a thicker,longer one too.

Next put everything back first coaxing in your pcb assembly back in to the frame, antenna socket/power input side first, Make sure the pull out wire stand & reset switch sub pcb are correctly positioned at the bottom. Look at photo number 4 at the top of this guide for the way things should look.
Lever up the corner of the pcb frame about 1mm or so with a flat screwdriver & hook in the lanyard into its fixing guide. Insert a small driver in the hole to line up the casing holes/lanyard loop.

Image

Now Pop the pcb frame corner back down.

Next, clean up the LCD window inside surface,

Image

and also clean the the LCD glass itself.

Image


Ensure the display foam edge is put back right .
Clip the front bezel back on.

Check everything is in place at both sides of the radio,the switches and knobs line up right. before replacing all the screws.

Image


Image
Now repalce those screws, remember the "bluetac hack" it makes life a lot easier when you dont drop screws into the abyss. A little bluetac goes a long way.

Image

Replace batteries and test.

Image

I never used the tecsun batteries supplied although they may be okay, I trust Sanyo Eneloops when plugging stuff in to charge, they are super reliable.
Tuned on Shanwick Radio, lets link up a long wire... I have sound.. she made it through the surgery ! 8-)

Image

The ssb received audio quality has improved significantly from stock factory reception.


A very solid 3 screwdriver job in the "haynes manual of radio servicing" if there was one. Quite challenging due to the poor quality factory solder used and limited space soldering and working around that 24 pin IC.

Make no mistake, this is no Realistic Pro-2006, smd transistors, capacitors all over the shop and cost cutting is evident throughout right down to the "tin can hard as nails solder".
Have fun !





Tecsun PL-600 SSB radio revisited

Having fitted the modification I wasnt happy with mounting the resistor at the back of the main pcb. Thinking about it, I should have perhaps applied 3m adhesive single sided foam instead of insulating tape to protect the resistor against a knock or drop of the radio.

In the end , The prospect of mounting the additional component on the reverse side seemed increasingly more attractive. I mentioned earlier that a Tecsun owner from Russia had done his this way using just the wire tails of the resistor itself but he had extreme difficulty with space constraints when re assembling the radio.He was a seasoned technician and radio amateur with a first/expert class licence so if he was struggling, a novice would probably do more harm than good if attempting this.

I looked around the unit and noticed there was ample room at the bottom of the radio at the reverse side of the keypad/lcd pcb.
Heres how I completed the modification.

Image

Strip out the keypad/lcd pcb by first unsoldering the ground wire link from the pll/logic board (marked A), then remove 4 small phillips size p000 screws (marked B).
Flip over the board taking care not to put stress on the ribbon cables.
Now you have access to the audio IC and mark pin 18 with sharpie.

Solder a 3 inch wire link on to pin 18 ( its very tight to get in there, about 0.75mm air gap between pins use an improvised signwriters stick made out of bluetac and thin dowel , hold this in the same hand as your iron, get in there on pin 18, rock steady..be brave !)

Closeup

Image

Next , solder a 3 inch wire link to the tuning trimmers RF shielding can (ground).
Solder the 1k resistor to your fly leads.

Image

Seal up with heat shrink tube.

Image

Glue gun blob your solder joint to both audio IC and tuning rf shielding can.

Image

Route cable from pin 18 in the gap between 2 capacitors to stop it from jiggling around in there. See above photo.
Re assemble radio and test.

My first attempt may have lasted the life of the radio but I was doubtful. A small foam pad would have been so much better than tape.
A knock or drop could have jolted the resistor & torn away the very small copper tracks from the pcb in the area of the audio chip making the radio beyond repair.

Im happier with this second method.
We have to experiment with these things to gain knowledge. :smiles:
I can confirm that everything goes back together with lots of room for the resistor, no lack of space at all.
From memory I think another user has experimented with a 473 polarised electrolytic in this position, I may try that next time I open her up but for now the reception is much improved with the resistor so I may well leave it as is.

Hope you enjoyed the trip in to the Tecsun PL-600, a fine radio for the price paid. Unbelievable value ! :biggrin:

I hope someone finds this useful. :wink:
User avatar
radiostationx
 
Posts: 117
Joined: Sat Jul 14, 2018 7:29 pm

Return to HF & Shortwave

Who is online

Users browsing this forum: No registered users and 1 guest