Hi all, I picked up a Sony D-4 Discman "for repair", which I've thus far not been able to get to turn on w/ either a DIY battery pack or a 9V tip negative DC wall adapter. While no clear damage to the PCBs based on a visual inspection, I went ahead and replaced all electrolytic capacitors (or so I thought...) w/ new ones, all correct voltage/capacitance. After still not being able to power the Discman up, I had another look at the board and noticed that there were two capacitor labels, C416 and C428, clearly marked on the board that as far as I can tell had not been populated when I received the unit (Image 8 + 9). This I figured since as I desoldered the old caps I'd kept them and labeled them to make replacing a faster process. So....I went to the service manual to look up their values, and neither capacitor appears on the parts list (see images 1 + 2). I then traced where they were on the board, went to the schematic in the manual, and haven't been able to find either in the schematic. (Images 3 + 4 are where I think they should be, but that could be up for debate) Oddly enough, C428 does appear in the board diagram (Image 5). C416 does not (Image 6/7). Is all this because the board is used for different models, and so not all components are populated in all models? That might make sense for C416, but then why is C428 also clearly shown on the board diagram, as well as the PCB itself, but not in either the parts list or schematic (from what I can tell). I'm new to all of this, so any help at all - even if it's just a hunch or educated guess - would be extremely helpful. Thanks so much for any help - really appreciate it! John
Welcome to the club!! The short answer: Yes, this happens allthetime... But. To be absolutely sure that C416 and C428 should not be there you can buy another D-4 to see if the same caps are 'missing'. The cheaper way: take a closer look at the board, if the traces rings for C416/C428 are yellow/copper they had never been used, if silver then solder had been used to maybe put caps there. If D-4 fails to power up, first check that DC jack is not cracked and 9V gets to the board. Check D401 protecting diode, it is there instead of a fuse and if previous user plugged 9V center-positive adaptor it opened. Then use your multimeter in mAmp mode to check how much (if any) current D-4 draws while playing dead. Should be Zero or 40-60mAmp. Then check if it powers up from 4V off the battery terminals. Do you have EBP-3 battery adapter for it? A few weeks ago I restored BP-3 battery and after that promised myself to never come close to D-3 or D-4 Discmans
Thanks Jorge! I’d suspected that diode as a good place to start for checking whether wrong adapter was used. Removed most of the solder w a solder braid to pull off the component to test and then read that once these SMD components are removed they shouldn’t be reused. Since I’d need to place an order for a new one I decided to continue checking voltages first. I can see that all three legs (including the NC no current leg) are reading 8.7V - not sure if that means currents getting to where it shouldn't. So next step will be to remove the diode and check if that’s the issue. One thing that’s confusing me a bit is the voltages on the schematic vs my own readings. Starting with the transistors early in the schematic (Q401 - Q412), I'll either see something different from what's on the schematic, or nothing at all. Q401, which looks to be For example, at IC802 schematic shows PIN 8 at 9V, and the other pins with voltages from 1.3 - 3.3 V. However I'm reading 9V (8.7V) at all pins. I can see that some readings are only if Discman is actively playing a disc, but these are not those. Does that mean that a transistor or resistor isn’t functioning properly somewhere on the trace before I get to IC802, or more likely that the IC itself isn’t doing its job? Thanks again for all the help! John Some add'l info if it helps - I was able to follow the traces around the board until I hit what I think is the volume pot, Q803, where I have voltage going in but not coming out. That's transistor IMD3. Just not sure if I should be seeing voltage coming out if the Discman isn't in Play Mode. I continued moving through the board, and saw voltage at components until the hold switch, at which point I get 8.7 V on one pin, 4.5V on another, and then 0 on the other two (looking at switch from above these are the two leads closest to the back of the Discman). Since obviously Hold is used to stop flow of current when switched on I was thinking that might be fine... The pins near the battery terminal were also reading 0, but since I was using AC adapter I thought that also was probably OK. I did order a BP3 and was going to try and rig a DIY battery pack, but when I finally managed to get it open - not an easy task IME - it was full of dust and other nastiness so instead connected wires to the battery terminals for external battery pack. Still no luck on powering on.
Also, your point about the solder points on the missing capacitors - one was solder free, one set of holes was actually fully covered over with solder - could mean that a capacitor had been there at some point and was removed, or that someone I guess covered them over?
All voltages are for D-4 when playing or in ServiceMode. But before going there check that you do not have a short: use your multimeter to check that it does not draw more than 500mA right now. And Yes! You can reuse desoldered parts, that is why we all have “for parts” Discmans. Just last week I scavenged voltage regulator off my working D-3 to fix D-7
Thanks Jorge! For measuring the current draw, should I be placing one probe on a test point early in the circuit, and the other on a test point towards the end of the circuit and measure that way? Everything I've just looked up online has me removing components and soldering leads into the circuit for testing, but thought there might be an easier solution. And when you say that all voltages are taken in play mode, does that mean that I should be pressing play, with the lid closed, before measuring voltages? Would I need to insert a CD into the player too, so that it stays in play mode while I'm measuring? Obviously my problems started because the player itself doesn't turn on, so not sure that pressing play is going to give me what I need. Thanks so much for your continued help
No, this is how you measure voltage drop. To measure current going thru the circuit you must connect your multimeter in series. the easiest way is to cut one wire of your power supply and attach your probes to them, so that current would flow through your tester. 9V all around IC802 is Not Good, looks like a short to me. But at least you found (the first) glitch: it is power regulator, something got busted above IC401 on D-4 schematics. And Yes,until you get it to Play (or set in ServiceMode) all those voltages downstream of the power circuit won't show you anything.
Thanks Jorge. So what I did was solder a lead to each of the input power terminals of the AC adapter input, and placed my multimeter between the power supply and positive terminal. I attached the negative lead directly to the power supply, same as usual. In the pics attached, you'll see that with the power supply set at 9V, the Discman is pulling between -0.1 and -0.2 mA. No change if I press Play, or move the Hold switch back and forth. So is that level of current (essentially no current?) to be expected? If not, does it help to identify or exclude possible faults? As always, thanks for the help! John
Do NOT engage 'Hold' switch, for now it is better to forget about it! You have no immediate shorts so you lowered your chances of burning more of this D-4 than whats already there: plug 9V power supply and start poking around DC-DC converter We have a few folks here with Electrical Engineering degrees (not me, unfortunately!), maybe someone will be able to narrow down the bust from your observation of 9V all around IC 802. Until then 'follow the money', start at DC jack and check that Q404, Q405, Q407, etc are at correct voltages. IC401 is at the center of your problems, by taking voltages off each pin might narrow down the bust. An easy option: different Discman models die in different but more or less consistent ways, so ask Kaosun (at kaosuncd.com) what is the usual problem with D-4. The guy restored thousands of Discmans and some of his diagnoses are weirdly spot-on!
Thanks Jorge! I’ll be reviewing your post more thoroughly tomorrow, but in the meantime, can I ask about that current reading specifically? Is it that because I’m seeing close to 0 amps, your inferring that I don’t have any short circuited parts on the PCB?
Correct! You may double-check your tester by plugging red lead into its Amp socket and setting it for Amps, if still zero you do not have shorts between the plug and On/Off circuit.
Thank you Jorge. Haven't gotten around to it this week, but hoping to dig back in this weekend. To test/improve my understanding, given that there are presumably no shorts between the plug and on/off circuit, does that mean that there areas on the board that don't necessarily sit in between the positive and negative terminals of the adapter / on-off / power circuits of the Discman? What I mean is that just because there are no shorts found when testing current from positive to negative DC terminal leads, that's not to say that there still can't be shorts elsewhere on the board? During initial component testing I had found some voltages that were off from their expected levels based on the schematic in the manual - for a voltage to be off, does that mean there must be a short somewhere on that rail that comes before said component, or are there issues other than shorted components that could be causing incorrect voltage at a test point? If at any point I'm bumming you out with all the questions feel free to ignore - your generosity in sharing what you know is almost too good to be true! Really appreciate it, Jorge. John
Oh - almost forgot! I'd noticed while going through the board v. schematics the resistor (?) that's circled in the pictures attached. My thoughts based on the manual was that someone had soldered it onto the board to put the Discman in test mode, but to be honest I know nothing about that other than what I see in the manual. Comparing it's location to where the manual says to add a resistor, it looks like it's close to the correct location but not quite. I could be wrong about that. Anyway, I imagine that if that's indeed what this is, it could certainly be having some impact on my findings. Am I right in thinking it's been put there to throw the Discman into service mode? And if so could that be causing the power issues and/or the funky voltage readings?
that is normal, the first Discmans had a few design glitches fixed only during production. Usually ceramic caps and diodes (as here), but even original boards had some bungees for when layout was getting too difficult for humans to calculate. This got fixed by early 90-ies, everything is clean and nice in later Discmans. Its a shame that by then (as with Walkmans and bboxes) the goal was cheapness, not sound quality. your first Q: since you cannot even turn Discman ON, something is wrong at the power supply side. The usual is a bad electrolytic, but since you did full recap it must be something else. Next "usual suspect" is a damaged board with traces dissolved by acid from leaking capacitor. Best checked when bad caps removed, no need to check continuity on all traces, just the ones with funny color. My D-3 which is pretty similar to your D-4 had a Lot of leaks affecting both sides of the board. Suspect bad transistor or chip next. They can short, or open, of go out of spec: having schematics with voltages marked helps A Lot here! Only when you make it turn ON, then you can check what is happening downstream from the DC-DC and voltage regulators. And you may have good news that everything works fine once it gets power. Or, as in case of early Toshiba Discmans, you learn that laser got burned by a shorted cap and you have to send it to kaosuncd.com to get new laser diode installed and centered.
Checking in on this topic. I have a D-4 in like-new condition but doesn't power on. This will be my next project.
