Repair of Exploded Digital Radio

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Introduction: Repair of Exploded Digital Radio

About: Thank you all for following me.

Two years ago I bought a nice gadget - DAB+, Internet , Wi-Fi, FM radio and media player - all collected together in one device. The radio was sold under the trade mark "Medion". This is a German company selling cheap, but according my opinion, not reliable electronics. (From four their products, which i bought, three of them defected short time after the fabric warranty expiration :-). Who knows - may be this is "planned obsolescence" ). Never mind. The radio was performing well during the last two years. By itself the parameters are not so good - the sound is like coming from old tin box, but I did not use the internal amplifier.Its volume was set to "0". I purchased a TA2020 2x20W amplifier on ebay, I connected it to the Linear audio output of the radio, which I supposed is directly coming from the output of the audio DAC. Having two JBL speakers as load for the amplifier brought me pleasure while listening the DAB+ radio transmissions. But each happiness doesn't exist long. One sunny day, during listening of a regional music station, a loud shoot was heard, and the radio became dead! :-(.

Step 1: Failure Analysis ...

I have opened the radio, and I have found that some damages were happened inside. The SMPS (switched mode power supply) module was defected. Few parts, starting with the SMPS chip, were blown up. On the pictures can be seen the big black hole appeared on the chip. I have searched all the damages, checking all the parts by ohmmeter, and I have found that the number of the burned parts is not so big - they were 3 :

  • the SMPS chip
  • one inductor (shown on the last picture)
  • a SMD resistor which was melted

I was not sure about the functionality of the opto-coupler, and I decided to replace also it.

To check the state of the HF transformer, I have to unsolder the SMPS chip, because it was making shorts between the different transformer windings and also affecting the other surrounding the chip devices.

In this moment my main problem was: "Which is this SMPS chip?". It was impossible to read its mark....There are a lot of SMPS chips, which have absolutely different pining. Mission impossible !!!.

But, in this moment the luck came back to me again. From the radio case, fell down on the table, the blown away plastic piece of the SMPS chip package, on which was written :"PR6203DP". New surprise... Research, continuing hours in internet, did not give me any information who is the producer of the chip, and where its datasheet could be found. Another black hole! I was hopping, that finding the datasheet, I could see the typical chip connection circuit, and what surrounding devices are used. Nope...

I contacted the manufacturer of the radio, and kindly asked them for the schematic.We had long conversation, but they were always refusing to supply the circuit ( For me this was strange - I think that each electronics equipment manufacturer should deliver, together with the product, its electrical circuit. That was normally the case few years ago.. For example, I have the full schematic of my TV "Grundig", which I bought 7-8 years ago.... ) Their explanations were, that the schematics is production secret, and should not be distributed. Very naive... their PCB's are mainly single sided and for experienced electronics engineer, the reverse engineering, could be matter of minutes....

Step 2: What to Do Now?!?

I was quite curious, and I did some additional research in internet. There I have found the following:

The Japanese company "Sanyo" is producing a digital radio model R227, which looks exactly like the "Medion"'s one. (see the pictures). This could be some explanation about the missing circuit diagram and the secrecy. I have contacted "Sanyo" support, asking them for their schematics, having in mind, that practically this is the same product. For me seems unbelievable, that if the external view of a device is fully identical with another one, something internally could be different. May be only the software....The "Sanyo" support, or what is remaining now from it ("Sanyo" was acquired by "Panasonic"), did not answer. I understand them - now they have other problems.

In this complicated situation, I have decided, to go to reverse engineering by myself, and to try to extract the schematic of the radio SMPS.

Step 3: The Reverse Design...

As I said, the reverse engineering was not difficult. The result can be seen on the picture. I suppose that I did some small errors in the part values, or I did not write it ( it is very difficult to define the value of SMD capacitor, for example, without precise laboratory equipment...:-) ). It can be seen that the schematic is simple, with small number of devices. The biggest efforts were given to filter well the output voltage, what is nice approach, and to try to reduce the EMI noise, induced in the AC power network. It can be seen that three different ground planes are used. Full galvanic isolation is implemented by the use of the opto-coupler device. This approach gave me faith, that the main electronics of the radio is not affected by the explosion. But I have to be sure. I wanted to supply the radio with external power supply module, and to be sure, that I am right. Here the main problem was, that I did not know, what is the generated by the SMPS module supply. Because the radio is digital, and it has a lot of microcontroller and other chips, and sometimes, they allow only 3.3V supply and the radio by itself does not have powerful output stage, I thought that the supply should be around 5-6V. I have found the 3.3 LDO, what told me that minimum 4.5 V should be required as input. The way to calculate the correct power supply was to look again at the circuit. There, as feedback error amplifier is used the chip KA431. I have found in internet that it can be programmed to switch at a given voltage, defined by two resistors. In this case R313, R316. The formula is the following:

V= 2.5V* (1+ (5.1+0.12)/4.7), where 2.5 is internally precise voltage generated by the chip.

This calculation gave me supply voltage value of ~ 5.3V.

I have applied 5V supply voltage by external source between the ground plane and the power supply output of the SMPS block and the radio started up. All functions were present.

Now were possible two different ways :

  • to supply the radio using external power source and to use it in this way totally discarding the defected SMPS module.
  • to try to repair the SMPS module, and in the case of unsuccessful results, to go for the first variant
I did not have any powerful transformer (12W) to try to go over the first way, and decided to try to repair the SMPS module.

Step 4: The Repair Works ....

The main task was now to find this exotic chip. In the beginning, I thought that it can be a copy of the most used chips, designed by Motorola, STI or NXP. I did not find any of them having the same pining.

Again the luck came to me. I have found that in the Chinese sites like Aliexpress this chip is offered, but in quite big batches. I have contacted around 20-30 sellers, offering the chip for the datasheet, but none of them was able to find it for me. This was very surprising for me - I was not able to understand how is possible to sell electronic components, without delivering the supporting them documentation. Finally, I decided to risk. I bought a batch of 10 pieces, for the price of about 10 USD.

After two weeks of waiting, the chips arrived home. To make my life easier in the future, I have soldered an IC socket. If the chip explodes some day, it will be easy to insert the new one. I have soldered the 1mH inductance.

Tha main problem was, that I did not know the value of R303. I looked in the internet for similar filters, but I did not find any methodology to calculate the value of the resistor. In the predicting its value, my thoughts were the following:

- Very small value is useless - it will short the 1mH inductance.

-Very high value is also useless - no current will flow through it.

- May be its resistance shall be identical to the impedance of the inductance at the frequency of the SMPS chip switching (not known - no datasheet found...or exist)

Finally I put 1.5K resistance....

Here, I would ask you all guys : if you have at home the same machine, or the "Sanyo" R227, could you check this value, to insert it in the circuit for the further possible use of it for repair works by whole the community of DIY hobists.

Step 5: Final Checks...

After soldering of all replacement parts (4 - additionally, I have replaced also the opto-coupler), I wanted to test the repaired SMPS block. I was not sure, how the block would work, and what the produced voltage should be. It could burn the whole radio. To test the module, I interrupted the current path from the SMPS module to the radio. I have unsoldered one of the filtering beads terminal (L304). To load the module I have soldered 10 Ohm 5W resistor at the output of the module. I have inserted the AC plug and supplied the module. It was quiet.... :-). I have measured the voltage over the load - it was 5.25V. I have recovered the all connections on the PCB and supplied the radio again.

It was functioning as before....

Step 6: The Pleasure of the Music ....

Having DAB+ radio, with nice amplifier and speakers, make the life brighter....

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    53 Discussions

    I also have this SANYO R227 radio. It powers up, goes to a blue "SANYO" screen, and stays there.. (locked up) Any ideas??

    Also, I saw the schematic -- Does anyone have TEST VOLTAGES to help troubleshoot??

    Loved the radio while it was working..

    Thanks..

    Hi to any followers of this thread,

    I have two Sanyo R227s, both of which have developed problems none of which correspond to those examined by Milen and other contributors. Problems originally arose when first one and then the other radio failed to connect with our LAN by wifi. When I took the back off them I discovered a wifi module in a usb port. By switching these from one radio to the other I was able to determine that one of the modules had stopped working. After studying the original module I found that the key chip was a Ralink, so did some exploring to find a replacement on the web. After some searching I found a seller in China that had one. I ordered two thinking that the second one might give up too. After a few weeks they arrived: they turned out to be Acer WU61RLs. So I installed these and the radios worked fine for a couple or more years (the original in the second radio eventually gave out). Lately a different problem has arisen: one radio refuses to make a wifi connection regardless of whether a still operational module is in place or not, and the other appears to make a connection and then recycles over and over again attempting to get onto the LAN. It may do so, but then recycles back to do a station update and go through the whole log-on routine again, usually culminating in a message like 'Network error'. Curiously, the radio seems from time to time to have lost its memory, and asks for the network key. None of this used to happen and I'm not sure where the organs are on the circuit board that store this information. If anyone has any clues, I'd happily desolder the failed/failing component(s) and replace it/them. I have no trouble operating either radio using a cable connection (unfortunately, however, I don't use the one of the radios where a cable is a viable option). Cheers.

    2 replies

    Hi Witgood,

    I never went so deep inside the hardware, except for the power supply part.

    I could try to find out which MPU/MCU is used. Also if any operation system is installed. This could be Openwrt. Using an USB to TTL serial converter ((based on FT232, PL2303, CH340G or etc.) you could try to communicate with the board - you have to search for (TX,RX) labels on the board and try to connect there.

    As terminal you could use Putty. May be you have to try different communication speeds. If you find some linux installation - you could try to update the firmware...

    You could also try to run some memory tests...

    It could be an interesting play.

    Please, if you find some additional info - share it here to be available for all interested.

    Regards

    Milen

    Thanks, Milen, for the suggestions -- I'll look into these in due course. I've tried from time to time to update the firmware (obviously before the usb wifi modules gave out), but on each occasion got a message saying there were no updates. A further thought I had is that the memory problems I've observed may be connected to the failed modules. I suppose it's not impossible that there's a memory chip in the module itself that is intermittently or progressively giving up the ghost. I'll report back after I've tried a few things. As noted above, the main chipset on the module is a Ralink RT2571WF. The Chinese supplier who sold me the Acer module mentioned originally that it had the Ralink 3070 chipset, but when I opened it up I discovered that it had another 2571. In any case I was told that the 3070 was backwards compatible with the 2571. When I originally ran into the problem I called Panasonic to see what they'd charge for a replacement module and was quoted close to Can $90 plus tax. The Chinese source was about $10 plus a few dollars for shipping.

    Hi,

    I have a Sanyo R227 radio that, like others here, would just flash the screen every few seconds.

    I have no real electronic repair expertise, but I have a multimeter, and I managed to repair my radio, partly with the help of this site. I always keep spare AC adapters from old electronics that get recycled, so I decided to bypass (and remove) the power supply completely. I connected an old 12VDC power supply to the white (+) and brown (-) wires that used to come out of the old power supply. Similarly, I connected an old 5VDC (USB) power supply to red (+) and black(-).

    Works great!

    I have a R227 Sanyo. Radio does not switch on immediately when plugged in. Opened and checked. No visible damage on power supply parts. There are four wires (red, brown, black & white). These are the output wires. How do I check them. The radio starts up some times after a few hours.

    14 replies

    Hi,
    Check if the power supply block of of radio looks like pictures in step 1.
    The supply block in my radio is separated board. I suppose in yours also. It should have 4 wires (2 high voltage - very dangerous to touch them - they come from the AC 220V/110V connector. The other two should be connected to the internal circuity of the radio. There you can measure if the power supply block is producing ~5V voltage.
    Use voltmeter. You can try also to disconnect the power supply board of the radio - (see the pictures... ) and supply the radio with external energy source - 5V AC/DC adapter.
    Of you do not find the problem, send me pictures of the block - then _ can give you more advices.

    Hello Milen, I have the same radio Sanyo R227 and a while back it failed. When plugged in, the lcd screen would flash briefly as attempting to power up.. it continues to do this every few seconds while powered. Sometimes if you unplugged it and quickly plugged it back it, it would turn on. Now it fails to turn on again. I have some (little) electronics experience so I replaced all the capacitors on the power board, and it did work for a while ..after a power failure it turned off and failed again with the same lcd screen flashing. Do you have any suggestions ? The power board doesn't look identical to your model.

    Hi RelativityT,

    Please check our conversation with ajaxa16.

    It could be that you have the same problem - in the audio amplifier (may be the caps...)

    Regards

    Milen

    Gentlemen: I am told that my unit has a resetting fuse wired into the input; hence the flashing display. When I restored both units, I pushed and held the button on the front until the flashing stopped. I then got a solid blue screen. Unplugging and re-plugging the unit (with the earphone jack in the correct phone outlet) restored the proper operation. Please note that the internal amp is still connected when you use the rear amplifier outlet so connecting to the external amp doesn't solve anything. There is a large array of capaciters in the internal power amp section and I assume that this is the source of our problems. I'll check the PS voltages in a couple of weeks when I take my vacation. I hope this helps.

    Thank you for updating me. I will check this too. Do you think the fluctuating voltage I measured on the power supply could be normal occurance with no load?

    Hi,

    the power supply block output voltage is controlled by feedback loop, and in the normal case no fluctuation of the voltage should be observed. In all cases some small load always exist and it should be enough for the functioning of the regulation loop. But, if some problem in the loop exist, then it work is disturbed. As first step try to insert a headphone in the jack to see if the problem still exist.

    I tried inserting headphone jack in front jack (labeled Reply?) and also LINE OUT in the back .It is the same 'flashing' screen problem with headphone inserted and powered on.

    Sorry,

    I forgot that you measured the PS also as standalone unit. Then,

    see my old posts - the problem is may be in the SMPS chip, or in the feedback devices.

    Hi,

    Try to measure the power supply produced by the power board.Is it falling or the problem could be a defected part inside the radio, which shorts the power supply causing some protection to trigger.

    The best would be if you disconnect the power boar from the other part and load it wit 20-100 resistor and to measure the voltage over it.

    As second step you could try to supply the other part with different power supply - it could be adapter or lm2596 board, but with some short circuit protection (if the problem is defected device in the main electronics).

    In this way you can determine if the problem is in the power board or inside the radio part. If the problem is in the power board - I suppose replacing one of both chips will solve your problem.

    Thanks for the reply! I don't have the Sanyo radio here but I can post a picture of the power board (detached from the main unit) . I think your radio from the outside looks the same, but inside you probably have a different power board from the R227. I think the best solution that you mention (easiest for me) would be to try using an external power source. If that works , then it would point to failed component(s) in the power supply. My question is what would be the Power requirements? I have access AC / DC power adapters. Is it DC or AC ? 12V/9V/6V? what voltage and amperage would be sufficient?

    Hi,

    It would be nice if you know what is the supply voltage.

    In my radio it is ~5.4V. I suppose that in yours is also close to that.

    In this case an AC/DC adapter like this:

    http://www.ebay.com/itm/90-240V-110V-to-5V-2A-AC-D...

    or this:

    http://www.ebay.com/itm/AC-to-DC-Power-Module-Supp...

    would work.

    I would suggest you to put a series resistor in the supply line 1-2 Ohm (only for the try) to limit the current and if a short inside the board exist to keep the power source safe. This can be also a small bulb (6.3V).

    More safe solution is to use ac/dc adapter for 12V but after it a regulated power supply like:

    http://www.ebay.com/itm/DC-AC-DC-LM317-Adjustable-...

    and to start to increase the voltage from 2-3V slowly until it reaches 5.4V observing what is happening with the radio - is some part extremely heating, or if a smoke appears.... :-)

    My opinion is that the problem is the supply board and nothing of this kind will happen. But...who knows.. Good luck.

    Thank you for your suggestions! The first link from the eBay seller you provided looks very similar to the Power supply unit that is currently in the Radio (from my memory). When I open the Radio I will take pictures and measure the dimensions, is it possible this could be a direct replacement? If so, would remove the terminals from the old psu and solder to the new psu.

    Hi,

    You have to be careful with the simple replacement of the PS boards.

    Sometimes they look exactly identical, but can produce different voltages. Practically the output voltage is normally set by the value of single resistor. If you buy a board with fixed voltage, changing a resistor you can set another voltage....

    OK I understand. I think the first step to get actual voltage from original PS if possible, but that may be problem if the PS is defective. Assuming the Sanyo PS board outputs 5.3V or close to it. Wouldn't a 5V rated PS be sufficient? or would 0.2 volt difference be a problem?