Hi everybody. Im working on a R707. It is a nice compact recordable Sony cassette player. I have replaced the rubber belt on the unit and I have it successfully spinning tapes. The issue I currently have is that I am getting no audio out at the speakers - not even static. To me this seems unusual. The unit itself doesnt look worn out and pinch rollers are in great condition. I have some theories in my mind regarding what it may be causing it. - Im not sure if the tantalum capacitors in the unit contain fluid but if they do they may have leaked have a high esr or shorted - Perhaps dry joint or ribbon damage - Perhaps IC damage The unit itself looks as if it has never been opened and stored well do i don't see how it could be damaged. Has anyone had any experience with this unit in the past or similar unit to help me with my diagnosis before I get more in-depth Edit: Ive noticed on a youtube video I found there is actually 4 electrolytic capacitors on the back of the board. I did not see them mentioned in the parts list. These could explain the reason I have no sound. I guess I'll have to take them off and test and replace Thanks in advance!
Tantalum capacitors don't contain fluid and are not a problem in general on cassette walkmans. IC damage I would put last, it's very unlikely unless the unit has been powered with reversed polarity. But then it's usually other things that get damaged like the motor servo. Dry joint would render audio if you press on the PCB in certain areas, while a broken flex cable will be visible. Those 4 SMD electrolytics are likely going to need replacement, although even failed ones render some low volume sound unless the connection to the pads is open circuit. Haven't worked on this particular unit, more famiiliar with 701C/702/EX80 which don't have any electrolytics, so can't tell for sure if those caps tend to go bad but you can measure them.
Thank you for your reply Valentin. With the tape playing and the unit covers all screwed back in, I tried pressing hard on the front main body of the unit and the back main body and suddenly i received some static noise. It is very low volume. I can hear some very out of calibration playback also, but the signal is severely attenuated. If the 4 electrolytes are coupling capacitors for the left and right channels Im guessing they are definitely faulty, possibly leaking and the case of the attenuated faint audio signal. I dont know however if I have permanently fixed the 'No audio' fault however as all i did was press hard. I will have to report back when I do a full analysis and replace capacitors
Can't find a manual for R707, but depending on amplifier topology it's possible 2 of the big 220uF caps are coupling caps. However the location of the caps isn't typical for coupling ones: these are usually close together and close to the headphone connector. Looking at F707 manual (can't find an R707 one), it uses the TA8145 headphone amp which has a topology that does not require coupling caps. Not clear what IC the R707 is using. Looking forward to the full analysis.
I unsoldered one of the 220uF caps and there was some small leakage and fish oil odor. The component test couldnt identify it and the multi meter couldn't record its capacitance. The multi meter also measured a constant 1M ohm where it should reach infinity when fully charged. So its partially shorted and unable to hold charge. I'll have to do a special order as I dont have any of these caps. From some research, I think the big 220uF caps job may not be inline capacitors, but "Feedback/Bypass Capacitors" positioned at the emitter of a transistor with a resistor to shape amplifier frequency response and gain. More specifically to compensate for magnetic tape high-frequency roll-off. Im not 100% certain of this though. Also, my analysis is also based off the F707 manual as I cannot find the R707 manual. There is another issue with this unit. It seems like I need to push with way too much force to get some (or all) of the push buttons to respond such as the play button. I believe they are tactile dome switch technology like most Sony Walkmans. Can we fix them without removing the membrane?
Looking in more detail at F707 seems very similar to R707. Thinking of it the 2 are likely identical, R707 just doesn't have the radio board in the door. C328 (220uF) is a filter for the 2.4V rail, important. C106/206 are feedback capacitors and those 2 can explain the no sound. C308 is a Vref filter, also important. Overall all of these capacitors should be replaced, would also check the THT one (C407) although that is related to bias oscillator so will only affect recording. With the switches ideally the membrane should be removed and cleaned. The force is required even if you press directly on the domes with your fingernail ?
Hi Valentin. My capacitors arrived today so I replaced them. I soldered in the new ones. I put everything back together as it was before. I can no longer get any operations to work. Play, FF, RR etc. the unit has power, Im pretty sure I have all the soldered on ribbons attached well without bridging. There is continuity from each ribbon wire to pad. I tried with remote and push buttons, no luck. Its a bit of a pain in the neck to get to the capacitor side of the board so I was wondering if there was anything else you could suggest I try before unsoldering the 3 ribbons to look at the capacitors again. Im not even so sure a poor connection on these capacitors could even cause the unit not to engage any tape transport operations so Im reluctant to think its capacitor related. Im not able to test this as I cant get any operations to work at the moment, but I notice when i press stop directly on the early tech "dome" its actually just the metal without dome it makes a click noise which feels right. But when I press the play, ff, rw they dont make that click noise and i dont feel any spring back or anything. Ive added a picture below of the button rail in case you have any ideas. I did give it a spray of contact cleaner but didnt improve any clicking noise. I dont know if they are heavily oxidized, they dont seem to be shorted because when it was working it wasnly playing, ff'ing or rw'ing on its own. Any ideas would be much appreciated
Indeed this fault may or may not be related to the capacitor replacement itself. However if these caps were leaky, it is possible that traces or vias were damaged, so keep that in mind. What I would check first is that the 2 voltage rails generated by the DC-DC converter (2.4V and 3.5V). When DD CTL control signal goes low (it should go at any button press) the DC-DC should turn on. Without the 3.5V rail the microcontroller will not run.
I didnt notice any trace or via damage so Im a bit confused as to what is going on. I think the dc-dc step up converter your talking about is doing its job although the voltages are a little lower than on the schematic. The AA battery im using is healthy 1.5v Without pressing anything, I measured IC702 (main IC) - VSS to VDD and measures about 3.2V (schematic says 3.6V) - VSS to CTL2 measures about 1.8V. (same as schematic) - VSS to CT D 3.2V (schematic says 3.6V) After attempting to get a VSS to CTL D measurement while pressing a button something weird seems to have happened. - VSS to CTL D is logic low 80mV or simmilar - VSS to VDD is now 1.2v - VSS to CTL2 is 0.8v now even later measuring 0.3V I dont know if I've damaged something by bridging ic pins accidentally or what. Ive tried taking the battery out and retrying but same thing Im getting these low values. I dont see how i could have wreaked the dc dc converter during these tests but perhaps I have. Any advice? I also checked the ribbon pins that go to the dcdc converter (ddc flex board ribbon) The first check - all the values were very low I then took battery out put back in: - all rails at the ddc ribbon looked somewhat fine 3.35v, 2.53v, 1.4v - the vss to vdd at the ic702 still however was 1.2v (it should be 3.6v) - after a minute or so the ddc ribbon values go back down low (3.5v rail drops to 1.5v, 2.4v rail to 1.9v, 1.5v to 0.95) Not even button presses bring these values back up
Not clear what you tried to do by shorting CT D to VSS. You're reffering to pin 7 (D CTL) ? As a general rule of thumb, you shouldn't short pins of the IC together, but through a resistor. Fact the voltages are there before even pressing any button may be an indication one of the buttons stays in closed position all the time. That would explain why there is no response at all from any buttons. The 3.5V rail goes through Q715, check what you have before and after it.
Hi mate. Sorry for the delay in response - we had fathers day and had some work commitments. I've tried some more testing and now I am even more confused Sorry for not making this clear. I didn't short CTL D to ground I was only conducting voltmeter measurments durring which (as the pins on the ic are soo tiny), I would have accidentally bridged adjacent pins together. My worry is that I may have fried some of the IC inputs. Ok getting confusing now because: I thought you might be right about this due to the fact that when i removed the battery and put it back in, seemed to work at at the ribbon i was (note was) getting 3.5v which would confirm the ddc step up circuitry was doing its job. However I was only getting 1.2v instead of 3.5v to the IC But now: I unsoldered the ribbon that goes to the dcdc converter and soldered it back on to make sure the connection was good I am now getting different lower readings: After removing battery and reinserting: - 1.5v battery is currently at 1.39V - DDC ribbon 3.5v rail: 1.39V (same as 1.5v battery value) - DDC ribbon 2.4v rail: 1.2V - Q715 B: 1.39V - Q715 E: 1.39V - Q715 C: 0.3V I guess we can see because the base is currently high that is the reason the transistor is OFF as its a PNP Perhaps the dcdc converter circuitry is working but Im not able to tell it to turn on? I tried pressing buttons and reinserting battery and the 3.5v rail stays at a constant AA battery potential now. I guess the only way we can move forward is to take out the dcdc converter and find a way to fire it up to bench test it? I was hoping this walkman would be and service but I was wrong
Shorting 2 pins of the IC accidentaly shouldn't cause a problem. Regarding the DC-DC, you can force the DD-CTL pin LOW by connecting it to GND via a 1K resistor and see if in that scenario you get the 2.4V and 3.5V outputs. If this works, means you're missing the DD-CTL control signal.
