Hello, I had quiet the troublesome time with this unit I can not figure out why this might be happening. I've done basic care already like cleaning audio jacks, pinch roller, head. Adjusting azimuth & speed. https://youtube.com/shorts/tRuFNWcOKKQ?feature=share Some on context: I start playing the unit, audio is coming through crystal clear but the second i trigger the auto reverse it goes silent. There's also an issue with one of the jacks where only the left side plays audio but same issue happens when I trigger the auto reverse. Image showing what happens when the auto reverse is activated. Any guidance would be greatly appreciated! On a side note at one point the motor PCB would heat up when ff was pressed but doesn't occur any more not sure if this piece of information is at all relevant.
Given the radio works fine on both channels (assuming this based on info provided) and fact radio output is fed into the Dolby amp, we can conclude the Dolby and headphone amps are working fine. So issue must be in the head preamp area: - REC/PB switch, FWD/REV swtich; - head cable or head itself; - mechanical: mechanism does not fully engaged the switch in correct position;
I've worked on 6 of these now, and channel-related audio failures are common. The first step is to see if the problem happens with both the radio and the tape player. If it happens with both, the flat equalizer cable would be the first suspect. If it happens with just the tape player, the first suspect is the flat ribbon cable from the head to the main board. These cables are extremely easy to damage when working on these units. And they are the components that take the most wear and tear during repairs. Mainly with faulty connections to the main board. The head cable is easily damaged getting caught near the volume control when mounting the chrome control panel. As Valentin said, the next suspects are the SW1 and SW2, which often need to be treated with contact cleaner/lubricant. I've seen bad solder joints on SW1 and SW2. The earphone jack and circuitry, and main amplifier stuff are ok if you sometimes get proper volume and stereo separation out of both channels.
Thanks for the information I wanted to make sure I went through all of it before I replied Also both of you were on the money when you mentioned ribbon cable. The one on the unit didn't appear to be torn but I've gotten different results replacing it with one from a j600. Although now my issue seems to be one with volume as my right channel is way louder then the the left. I think it might be with my soldering I have seen different ways that the ribbon cable is soldered to the board.
Use a toothpick to press on the cables connections and see what that does. Also, the soldering on the adjacent SW 1 looks dodgy. I have one where the factory soldering on both SW1 and SW2 was incomplete. It is the one I have in the best condition because it wasn't used because it never worked properly. It is possible for the ribbon cables to have breaks between the embedded trace and the cable's exposed terminal. This is very hard to spot. Relatively easy to locate using an ohmmeter. If that's the case, you have to scrape off a bit more of the ribbon cable insulation to expose some trace to solder to. You might also try moving the 5 equalizer knobs while playing it. Twice I have seen where one of the sliders cuts volume in some positions. But probably this would affect both channels at the same time, and should affect both radio and tape operation. I assume the soldering between the ribbon cable and the head is ok. If you have swapped this cable I assume you've removed the chrome Play button properly without breaking it. And removing the head means adjusting its position when reinstalling it. You might also want to poke around at the volume control solder points. Again, this would affect both radio and tape operation. The volume control mounting depends on the solder joints for attachment to the main board, so they are subject to flexing. I have seen one failure of those points. I found securing the batteries while testing these things without fully assembling them was annoyingly awkward. Now I have an RB-100 external charger/power pack I can plug into the players. Which makes testing much easier.
Quick update: the left channel has completely gone silent Only thing that I changed was re soldering Sw1 Did a quick continuity test on the ribbon cable and all traces have a stable connection The equalizer & volume slider don't seem to be the problem it acts the same on the radio/fwd/rev playback. Also yeah I also picked up a rb-100 a while back its a time saver!
Other than the earphone jack itself, I'm at a loss. Maybe the circuit diagrams in the service manual could help. The fact one channel works would help in comparing continuity.
