I would like to know the maximum current draw of the CX20084 motor drive IC used in the Sony Walkman WM-D6C. I would guess that would be in fast wind mode.
Note most of the current flows through the drive transistor Q601 (2SB1063), not through the IC itself. If we assume a current gain of 100 (which is in the ballpark of datasheet spec), that means the base current is 100 times smaller than the collector current. The current draw of the IC is the specific quiescent current of internal circuits + the base current of the drive transistor (with Ic=150mA, Ib=1.5mA). Maximum motor current draw happens in FF/REW at the end when motor gets stopped, before auto off activates. The service manual gives a spec of ~150mA draw in FF/REW, but that is during FF/REW not at the end. For exact values, you will need to measure as there is no datasheet available for the CX20084 to give us the quiescent current.
Thanks for your reply!! I had temporarily forgotten that there was an outside driving transistor, which, as you said, supplies the drive current for the motor. So, only a coupla mA at most. A 4v LGO regulator (MCP1702-4002E/TO Microchip Technology | Mouser) in series with the power feed to the CX20084 should work fine to protect the chip from overvoltage. And a low forward drop Schottky diode (1N5818RLG onsemi | Mouser) to protect against reverse polarity. Eh?
1N5818 will have a forward voltage drop of ~0.2V@150mA, meaning a power dissipation of 37.5mW. Also with NiMH cells 4.8V-0.2V = 4.6V. With the typical dropout of 625mV, you have only 25mV of margin for the 4V output. The solution for this problem is a "smart" diode like LM74610.
If you look at page 8 of the datasheet for the MCP1702, you will see that the dropout @150mA is only 0.2 volts at 150 mA @ room temperature for 5 volt output. Probably a bit more dropout @ 4 volts; but still enough room. The LM74610 would be an elegant solution but requiring a custom PCB. Deb64's solution of an AP2210 is much simpler, though it also is SMD and requires a custom PCB. I am wondering if it is necessary to limit the voltage to the Q601 drive transistor as well as the CX20084. Would the lower voltage to the 2SB1063 lower the fast wind speed?
doorz says: "Same rewind speed with 3.7V or 5.0V, just tested with full/empty battery "mix" So I think the MCP1702 with a 1N5818 in series (for reverse voltage protection) applied to the CX20084 supply ONLY will do the trick. Since the current draw then would be quite low, no heatsink should be necessary.
Motor speed is independent of Ve of Q601 and Vcc of CX20084 as long as they're above certain thresholds. So yes MCP1702 + 1N5818 will work fine. You only need to supply the regulated voltage to the IC.
Thanks for your reply. Now how about over-voltage to the remainder of the circuits? I saw posted that some wall-warts marked as "6V" actually put out as much as 7.6 volts. Looking at the schematic, I can't see anything that would damage unless (maybe) the DC-DC converter. Speaking of which, I have a diagram that I got somewhere that indicated that the schematic is wrong and the INPUT to the DC-DC converter is actually pin 3 and the OUPUT is pin 1. Is that right?
Yes, the DC-DC converter schematic is flipped horizontally, it's an error in the service manual. This is obvious if you look at the internal schematic as that voltage divider has to be on the output. Also the topology itself only makes sense this way. Wanted to edit the schematic myself, but these service manual PDFs are locked and cannot be edited. CX10043 VU-meter IC has R813 current limiting resistor. IC701 also has a current limiting resistor R716. Most of the audio section is operating at 10.8V, so not a concern here. DC-DC converter will be fine as input current will be lower with higher voltage. However I can only recommend against using an AC adapter that outputs 7.6V on the D6C, especially since some people may only read this statement and draw the conclusion it's fine to use it without the mod. As far as adapters go, all linear ones that are not regulated will output higher voltage with no load. These will also have variations with mains voltage. If such an adapter is to be used, I recommend adding a regualtor to it. If it's a switching one, it should be checked for high common mode voltage. Generally speaking, if you want to use your D6C on an AC adapter, choose a good quality one, not a cheap no-name.
Yes, the WM-D6C's DC-DC regulator makes a LOT more sense that way All very good advice. Most wall-wart power supplies are not very good, so I will build my own with an LT317 regulator and Elvee's brilliant denoiser. BTW, what lubricants do you use for the WM-D6C? I have some Lubriplate 105.
Lubriplate 105 is a generic grease designed of automotive applications. As far as grease goes, would prefer white lithium grease to this one. For all rotating parts' shafts I use watch oil, including the FF/REW idler arm. There are few points where I use grease, like flywheel thrust adjustment screw.
Thanks, I'll check it out. Now, where is the best place to locate the 1N5818 Schottky diode for reverse voltage protection? It would seem ideal to put it in a place on the PCB where it would protect against reverse-voltage external supplies as well as protecting against someone putting the batteries in backwards.
If you want protection from both DC in jack and batteries, you will have to cut quite a few traces. In my opinion putting all 4 batteries backwards is very unlikely to happen, so don't see a particular need for this protection. Problem is mostly on the adapter, because it's center negative and most modern/non-Japanese ones are center positive. Where you place the diode really depends on what you want to protect from reverse polarity: the whole circuit, just the servo, servo + DC-DC converter etc. If you want to protect just the CX20084 itself, you don't even need the LDO and 1N5818, a smaller 1N4148 will work just fine for this purpose. From what I've seen so far, the most common failures in regard to reversed polarity are as follows: - burnt CX20084 is the most likely and will always fail; - burnt NPN transistor + inductor on DC-DC convertor is unlikely but can happen; - shorted capacitors is even less likely, but seen it happening on the SMD board (C318) causing no audio;
Yes, you are correct that reverse voltage from an external power supply is MUCH more likely than reverse battery installation. But, if I could find that point on the PCB where the feed from CN301 meets the battery + connection, then I could put the 1N5818 there and it would protect both. I admit I am going just from the SM as my WM-D6C is not in my hands just yet.
"For all rotating parts' shafts I use watch oil, including the FF/REW idler arm." Thanks, but in searching for 'watch oil', I get a bewildering number of choices, many seemingly oriented to the guy who wants to repair hundreds of different watch models and thus needs many types of oil. Can you recommend a specific brand of watch oil?
In regard to the diode I attached a picture. The simplest way I see is remove that jumper wire and add the diode there (it may require enlarging the holes). Then you only need to cut 1 trace and reconnect the rest of the circuit after the diode. This is assuming we are talking about the through hole board, as the SMD one is different. As far as oil goes, exact type of oil used is not critical that's why I stated "watch oil" in general, because any watch oil will work. You can use a watch oil that comes into a pen-like recipient which is easier to apply, like this one: https://www.ebay.com/itm/315342449092 Can also use something like Moebius 9010, but these come in very small bottles on 2ml. But don't expect to see differences in this particular application. As a sidenote, you can see a Hitachi service manual (picture attached) which recommends 10W40 engine oil, which again tells us the exact type of oil used is not critical.
@Valentin: Thanks! Your expert help is much appreciated!! I note that your screen shot of the PCB shows (in pink) the traces on side 2 of the PCB. The WM-D6C service manual I downloaded from hifi engine does NOT show those; it is only black & white, completely eliminating those traces. Where can I get a shot of the whole PCB like the one you show?? That watch oil in the pen applicator looks good; I'll order one!
You can find the PCB diagram here: https://www.petervis.com/manuals/sony-wm-d6c/pcb-and-wiring.html It's in black and white, but the traces are visible. The color scan I have seems to have been downloaded from https://freeservicemanuals.info as it has a watermark. Traces shown in red are power lines, not from layer 2, since this is the through hole PCB as I already mentioned which is a single layer board. If you're looking for the SMD diagram, that's under Supplement 2 of the service manual, pages 5,6,7 (page 25 of the PDF file).
Thanks for the link to the color service manual; it does indeed show those pink traces but also the voltages on the schematic are MUCH easier to read. I also note that the regular electrolytic and tantalum capacitors on the WM-D6C (through-hole version) are about 40 years old and thus the unit may be ripe for a recapping job. Have you undertaken this? With 33 regular electrolytics and 51 tantalums, it's no simple task.
I typically don't replace capacitors just because they're old. Rather, I prefer measuring them on LCR meter and compare with typical parameters of new good quality ones. If, on average, I see significant degradation (decreased capacitance, increased ESR etc.), then can draw the conclusion it's a good idea to replace them as preventive maintenance. In regard to the D6C, the THT board is reliable and it's uncommon to see issues with capacitors. There are situations, for example, when the output coupling caps go bad creating popping noises or even no sound, but it's not something common. SMD board is significantly more problematic, despite it's much newer. Replacing all 84 polarized capacitors just for the sake of it is not worth it in my opinion. If the walkman works fine and sound is good, I would leave the caps alone.
