Tecsun PL-600 teardown / ssb audio mod (pic heavy)
May 27, 2017 22:41:28 GMT 1
Beemer, G-PHIL, and 3 more like this
Post by radiostationx on May 27, 2017 22:41:28 GMT 1
Tecsun PL-600 SW Radio Improvements to SSB audio modification.
The Tecsun PL-600 is a great radio for thre price, some time ago I gave a thumbs up for it on this forum.
derbosoft.proboards.com/thread/17331/low-cost-communications-receiver-airband
A real bargain for the price.
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 !
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.
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.
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.
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.
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.
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.
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.
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 !
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.
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.
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.
Now Pop the pcb frame corner back down.
Next, clean up the LCD window inside surface,
and also clean the the LCD glass itself.
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.
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.
Replace batteries and test.
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 !
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 pro-2006, smd transistors, capacitors and cost cutting is evident throughout right down to the "tin can solder".
Have fun !
Hope you enjoyed the trip in to the PL-600 and I hope someone finds this useful.
Mike
The Tecsun PL-600 is a great radio for thre price, some time ago I gave a thumbs up for it on this forum.
derbosoft.proboards.com/thread/17331/low-cost-communications-receiver-airband
A real bargain for the price.
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 !
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.
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.
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.
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.
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.
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.
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.
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 !
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.
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.
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.
Now Pop the pcb frame corner back down.
Next, clean up the LCD window inside surface,
and also clean the the LCD glass itself.
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.
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.
Replace batteries and test.
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 !
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 pro-2006, smd transistors, capacitors and cost cutting is evident throughout right down to the "tin can solder".
Have fun !
Hope you enjoyed the trip in to the PL-600 and I hope someone finds this useful.
Mike