Tuning Problem And Issues In AC Adapter Solved In PHILIPS Radio RL205/00
This radio was brought by a recently added regular customer with the complaint that the AC adaptor was not working and the tuning was with crackling noise. I opened the ACA, which had multiple voltage selector switch and a polarity inverter switch. Let us have a look of the inside:
As you can see, there was only a 470uF/16V capacitor inside! One of the flimsy secondary windings was open and I decided to replace it with a proper transformer and circuit to provide 4.5V DC. Though I tried with a 0-6, 500mA transformer with the 5A regulator, the input voltage was not good enough and therefore changed it to 0-9V, 500mA.
After ensuring that the TX was seating properly, connected a bridge rectifier to the 0-9 V AC and provided two fixed caps of 100nF/100V across the diodes. For the main filter, I used 2200uF/25V. The input voltage was checked to be around 13V. Then provided a heat sink for the 7805 IC and connected two 10uF/63V at the inputs as well as the outputs apart from the fixed caps shown in the following picture:
The 5V output was good on checkup. Then provided one IN4007 at the output to drop half volt and added a 2200uF/16V smoothing cap there also. The output was 4.641, which you can see in the second picture above. The next task was housing the circuit inside the secondary section, which I managed by providing lead wires for the regulator.
Though the finished work had a clumsy look, performance was superb when connected to the Radio, as there was absolutely no hum. It worked as though from a DC battery. Let us have a look at the clustered ACA:
Then connected the output wires after checking which pin should get which polarity. In the socket there was a marking that positive should go inside and negative should be in the outer. After ensuring a stable power supply, the next step was tuning stations and find out what made the crackling noise. In this radio, inside of which is exposed below, a 100K potentiometer was used for manual tuning instead of a ganged condenser.
As I knew that the 100K VR was the culprit for making crackling noises, replacement of which was not available in the market, I dismantled it and first cleaned it with IPA and then applied lubricating oil, fixed it back and rotated the spindle a few times clockwise and anti-clockwise to enable self-cleaning. (The second picture above would show you the dismantled VR.) Then fixed it and tried and found that the the crackling noise had gone! The next task was fixing a new TRA as the one in the radio was broken. I used a good quality colour matching TRA after removing the old one and fixed the following extra fittings that are necessary for proper seating of the antenna at the rear.
The two copper washers as inserts at both side of the fixing screw are very essential to make proper contact and smooth tilting of the TRA to different directions for better pick up of signals.
Lubricated the volume control and band switch and cleaned it thoroughly by operating them vigorously. Then fixed the back cover with its screws. Mission accomplished with derived satisfaction that got collected!
This article was prepared for you by Parasuraman Subramanian from India. He is 76 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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Albert van Bemmelen
June 13, 2026 at 2:56 pm
As usual another successfully fixed power supply repair Parasuraman!
Often older power adapters like those used for Commodore Amiga and or C64/128 computers become dangerous. Because after 30 years or more their adapter output voltage may suddenly increase and instantly kill the sensitive complex MOS chip circuits in those computers. Which can be avoided by plugging on an quite expensive small protection circuit we can buy for on the output power plug of those adapters that immediately blocks the output voltage at a sudden unsafe voltage rise.
Or simply make a modern new and safer smps controlled power adapter which I already did for the C64/128 and am making for the Amiga/C128 (both use the same Square DIN-5 power supply connector and voltages). And these Amiga/C128 power adpters can be made and assembled even without any soldering as instructed in this article: https://www.youtube.com/watch?v=mibbEzajOI4
The instructable on Youtube even includes the nicely designed 3D printable case for those safe and also universal usable modern power adapters that are completely fed by small and very powerful USB-C PD adapters and controlled by two small boards that fit in the case. Giving 5V, -5V and 12V with -12V output voltages as also needed by 24 pins desktop powered computers.
Parasuraman S
June 13, 2026 at 4:28 pm
Many, many thanks for your expert comments packed with valuable techie info, link and guidance, dear Albert! Shall visit the link and study further on these prospective ways!
Albert van Bemmelen
June 13, 2026 at 9:38 pm
About the in my above comment mentioned universal USB-C PD adapter to 24 pins output board voltages that I received today: There is no -5V output but an output voltage of +3.3V instead! Next to the already mentioned +12V ,-12V and the 5V outputs.
My also today received GaN 240W PD adapters (priced at 3,35 euro each) are easily capable in providing 4A at its USB-A 5V DC ports, 2.3A at 9V DC and 1.7A at 12V DC on its multiple PD USB-C output ports (4 x PD USB-C + 4 x USB-A 5V).
Albert van Bemmelen
June 13, 2026 at 10:42 pm
Another also today received GaN PD USB-C power adapter with 140W marking was even better in providing upto 35W at 12V DC delivering 2.5A max! Which makes the 240W overvalued less qualified to power my Amiga 1200 or C128 Commodore computers! So do net get mislead in thinking that the 240W PD USB adapter is better in providing more current/power which it does not! Also because the 140W adapter also came with an excellent thick sturdy USB-C/USB-A PD cable.
Parasuraman S
June 14, 2026 at 11:34 am
Many thanks for this clarification and guidance, dear Albert!
Parasuraman S
June 14, 2026 at 11:33 am
Many thanks for these additional valuable info, dear Albert!
Albert van Bemmelen
June 14, 2026 at 5:09 pm
Addendum: the assumably higher power 240W adapters completely failed working attached to the PD voltage selector and the 24pin power board! Even when set at its 12V max output USB-C voltage when tested! Only the 140W adapter worked when 15V or 12V PD input was selected. The 240W adpters always gave only 5V max even when it should also give upto 12V output!
Narinder Singh
June 14, 2026 at 2:15 am
Genious
Parasuraman S
June 14, 2026 at 11:34 am
Many thanks!
Mark J
June 14, 2026 at 3:05 am
I come across that problem a lot. The variable resistors going bad and causing the crackling noise. Most of the time they just need to be cleaned due to corrosion. Thank you for sharing Parasuraman.
Parasuraman S
June 14, 2026 at 11:36 am
Unfortunately, these VRs are not available in the market. Perhaps the company has an OEN understanding with the buyer, to monopolize the service. Many thanks, dear Mark!
Philip
June 14, 2026 at 4:51 pm
Thanks. Where would I, if required (not in a radio), connect an ideal DC fan in the created power circuit ? I think fans cool down hot components more effectively than the slow heatsinks, though at the expense of additinal power that is worth it. Some radios are now out for use during the football worldcup tournament. In my area some radios and TVs are are set to come on to wake up die-hard fans way long past midnight when the football matches kick-off.