Lovely PHILIPS 6.1 DVD Receiver Amplifier Model LX-3900SA/69 Saved From “Death”
This DVD player was brought by a regular customer from a faraway distance with the complaint that the player was lying unused for quite some time as the eject was not working and one CD was stuck inside. He had given it to one of his friends, who was a half-cook technician, just to remove the stuck CD and after removing the CD, his friend told him to dump it as it was not working; rather going to standby mode. The customer carried this player in a bag and came by bus and I picked it up from the bus stand, on my way to my duty in the hospital, during which he collected his two other players that I had serviced, both of which were inside a carrying suitcase, but a bit heavy.
I took this up for service as soon as I got some free time and opened it for a thorough cleaning. I saw rust formations in a few places and symptoms of water or some such other liquid leakage inside. So, dismantled the whole player. Forgot to mention that I checked the complaint and found that the set was going to standby mode immediately on switch on.
Let us see some pictures:
From the pictures which show even loose rust lying on the board, one can very well understand why the customer’s friend advised him to discard it. The last picture above would show the rust formation on the cabinet bottom, which was a result of some liquid settling there. In this player, the Amp board was at the rear and the PS board was in the front, just before the front display. I too almost decided to confirm dumping as the extent of damages that had taken place in this SMD fit, double sided PCB set were massive; but something within me urged to proceed further and make an attempt to revive it. I just cleaned the PS board thoroughly using IPA and board cleaner spray and got rid of the rust and dust from it. I also cleaned the other boards using IPA and cleaned the FFC cables using rubber eraser and fastened the insert assist blue pieces at the end with a tape in order not to dislodge it. Then cleaned all the connectors and lubricated those which can be done. As I had already downloaded the service manual of this set, link of which is provided below, I had ease in understanding the circuit and its functions:
https://elektrotanya.com/philips_lx3900sa_ver1.1.pdf/download.html
I gave power to the PS Board and checked whether the outputs were present and found these to be ok. I did not connect the Amplifier board as it was in a bad shape and my guess was the defect in it could be the reasons for set going to standby. I connected the boards keeping it on the table and applied power and checked whether it had life enough to proceed with the restoration work. I was amazed to see that the set worked perfectly responding to the commands like an obedient servant, without going to standby!
So, the culprit indeed was the amplifier board. I loaded a few CDs too in the above condition and watched the display in my 4” black and white CRT TV that I use for checking DVD players. The set was working perfectly. The cable from the eye unit was badly twisted and damaged. So, I replaced it. As the eye unit was reading and playing very well, I did not do any cleaning of it for fear that it might get spoiled. I just allowed the barking dogs to be barking, contrary to the old adage ‘let the sleeping dogs be sleeping!’ (LOL)
Next focus was on the Amplifier Board. I dismantled the heat sinks and was not surprised to see dark patches of explosion that had taken place around two of the three SMD ICs. Just see how the intuition helped to try the set without connecting the Amp Board!
The first picture above would show you the marks of explosion. In the third picture what I have marked is the set of components that got charred but held in place because of the thick vibration-preventing paste applied on the board.
There were no cracks or burst marks on the ICs. But these components that got charred were in the input and therefore, the shorting of the ICs probably due to liquid seepage was suspected. I fetched three ICs from the local market, as it was surprisingly available with one vendor. Then spending a lot of time, removed the dried paste as it could conduct and cause shorts. Removed the six 470uF/35V caps and three 22uF/100V caps, which incidentally were bulged and one had burst too. All these were held in place because of the paste. I removed the three ICs using hot blower and removed the paste using IPA and gum remover liquids. All these works were time consuming. A few of the already detached and charred SMD components came off with the paste and there was no way of knowing the values!
But luckily the service manual came to my rescue. I cleaned and cleaned the boards thoroughly and even removed the six coils, which had marking on one side like a capacitor as the direction of winding should be even when these are connected. The cleaning liquid can settle inside the crevice under the coils and that is why I removed these too.
Following snaps would show you the coils in place, but these were removed and re-fixed later.
I am giving below an extract of the amplifier circuit. The board had a clock generator, which was mixed with the audio signals before amplification and removed at the output. This is to boost the signals like how it is done in IF stages of a radio. In fact, this is the first time I am seeing such a circuit.
6-channel class-D amplifier
Basic operation of a class-D amplifier
Basically, the output stage of a class-D amplifier outputs a continuous square wave swinging between positive and negative power supplies with a fixed frequency (“clock” frequency) far beyond the audible range. The duty cycle of this square wave is modulated with the audio signal. The output is followed by a low-pass filter which eliminates the clock frequency and allows only the audio signal going to the speaker. See simplified drawing below.
Compared to a conventional power amplifier the benefits of the Class-D amplifier are:
- higher effiency
- lower power dissipation
- smaller heatsink required
- smaller mains transformer required
The main disadvantage of this concept is:
- The amplifier is operating with a high-frequency square wave at high amplitude and currents. This requires special precautions to prevent excessive electromagnetic radiation (EMC).
These are the extracts from the relevant pages where they have very clearly explained the function of the amplifier circuit. Now you know why the direction of the coil at the output was important.
I replaced the missing components taking help from the circuit and fixed the three ICs and retouched all the SMD components in the amp stage. I also replaced the electrolytic caps. Though this looks very simple from a single sentence, it took hours of minute and precise work and focus and concentration as the contacts should be proper. I cleaned the board again thoroughly and even checked the solder joints in the microscope.
The finished board looked very neat and clean. The soldering work done by me also looked too good even for me to digest it! (LOL) Before fixing the heat sinks, I just connected the amp board to the power supply and checked whether the DCs were dropping. It was ok. Then connected the inputs and control FFC cables from the main board, connected just two speakers and played a CD. The sound output was amazingly superb!
Removed the Amp board again and fixed the heat sinks which had two screws underneath, with clip locks on the top and fit the board back to the set permanently like how it was before. The rusty iron plate cover was soldered at five points in the PCB. Though I had removed the rust, the marks remained.
Allowed the set to run on all modes; CD, Tuner, Aux in etc. and found it to be working superbly well, which I covered with videos and shared with the customer. His astonished reactions were very amusing for me! To tell you frankly, the clarity and quality of the sound output was immaculately impressive! Mission got accomplished with greater satisfaction finding its collection bag very easily!
P.S. I forgot to mention that the tray eject problem was solved by replacing the rigid belt. The old belt got misplaced and that is why you don’t find it in the picture of replaced components.
Do you all now agree with the use of the word ‘lovely’ in the caption?
This article was prepared for you by Parasuraman Subramanian from India. He is 74 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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You may check on his previous article on Massive Destruction Caused By Lightning In This NATIONAL RX-C47F TWO-IN-ONE
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16 Comments
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ANTHONY PATERSON
December 20, 2025 at 4:53 pm
Your appetite for repairs knows no bounds. Another repair that would be beyond the average engineer however, you are in a class of your own! Well done and thank you for sharing.
Parasuraman S
December 20, 2025 at 7:35 pm
Many thanks for your encouraging comments and support!
Albert van Bemmelen
December 20, 2025 at 5:54 pm
Very 'lovely' repair dear Parasuraman! And also very enjoyable to read too! With your unperturbed and decisive urge to revive even the most massive extent of damage on sets that normally simply would have been discarded and scrapped. And many thanks for adding the link to the 59 page Philips servicemanual that may come in handy if this set ever crosses my path!
Parasuraman S
December 20, 2025 at 7:37 pm
Many, many thanks for your appreciating and encouraging comments, dear Albert! I value this in Gold and diamonds!
Tito Kanshulu
December 28, 2025 at 5:14 pm
A very appetizing repair article which goes along with an in-depth knowledge sharing. Thanks Parasuraman for the article. I have been boosted of my energy of not giving up easily.
Parasuraman S
January 4, 2026 at 3:05 pm
Many thanks! Glad to know it was useful!
R MURALI
December 20, 2025 at 9:14 pm
Thank you, Sir, for sharing the repair work. I am very much interested in reading your Repair Articles. Your Knowledge and passion for electronics.
Salute to You, Sir ....Namaskaram
Parasuraman S
December 21, 2025 at 9:53 am
Namaskaram! Many thanks for your wonderful encouraging words!
Mark J
December 21, 2025 at 5:25 am
Parasuraman great article. Thank you for listing the link for the service manual. I might need to refer to it someday if I come across one of those units to repair.
Parasuraman S
December 21, 2025 at 9:54 am
Many thanks, dear Mark!
Muykit
December 21, 2025 at 11:26 pm
I beg that I may not be misunderstood for my mistaken view. The DVD player has a sound amplifier working in a confined environment and without a fan, at least, so do the pictures show, or do not show. Do I need to think very hard to know what probably may have caused the amplifier to throw in the towel, unless stated otherwise ? Most of the DVD players without audio amplifiers that I used to see consumed a paltry <10 watts, so a general 80 watts consumer for a DVD player with an audio amplifier definitely makes the additional audio amplifier in this particular case responsible for the extra watts supply. For such a high power consumer that likely produces much heat, its a big mistake that its denied the natural right to breath air in and out adequately as a necessity and a general rule for that matter, for proper functionality. When its pushed to the wall, complaints of being denied its rights will, take it from me, wake up sleeping dogs in some quaters and the DVD will certainly come to a grinding halt.
Parasuraman S
December 24, 2025 at 3:01 pm
Good observation. It indeed has a cooling fan, and it was found working very well when hot! Many thanks!
Yogesh Panchal
December 23, 2025 at 4:37 pm
Good fix!Sir
Every Memory is going in air as a storage, the technology of cassette players and DVDs needs to be revived to save & share memories.
Parasuraman S
December 24, 2025 at 3:02 pm
Yes, technological advancement has already swallowed many lovely antique models! It will continue to gulp! We, technicians, have to keep running ahead not to get gulped! Many thanks for your valid comments!
Lee
December 25, 2025 at 6:04 am
Hi Parasuraman.
You can use automotive degreaser to remove heatsink paste. I discovered this after trying it on a Pc cpu.
It literally dissolves to a liquid an just wipe away.
Parasuraman S
December 26, 2025 at 9:33 pm
Many thanks for your suggestion. I shall try that soon.