Looking for a cassette reversing mechanism fix - Page 1
Forum section: electronics / beginners

author: goingjag
author_rank: Contributor
timestamp: October 04, 2014, 01:24:18 am
content: I had planned to use my cars stereo cassette player with an ION bluetooth transmitter. Bare with me, it's not the usual problem.When it continually reversed, I assumed it was a problem with the unit not sensing a tape in place.So I dug out a cassette and tried it and it does the same thing - plays for a couple of seconds pretends to reverse then goes back to side 1 and plays for a few second etc. Purposely switching to side 2 just results in an immediate switch to side 1 and/or an eject of the tape.The reversing mechanism is either optical or magnetic is my guess. The underside of the wheels used to spin the tape are marked by placing black (or very light magnetic tape in 6 separate segments so you have black silver black silver etc.On the cover above an "IC" is mounted above each wheel. It has two lines in and two out. Although the "IC" is a single piece each line is soldered to it's own copper trace on the circuit.On searching the net, I didn't see a hall effects that had 4 legs on them, and I cannot see any way in which these things are optical lens, they look black although they are shiny like when black epoxy is used to cover something. If they are optical I would think at least one should be a clear lens, but then that's why I'm here in the beginner section.Since I won't really be using the cassette, all I am really looking to do is "fake out" the reversing logic by bypassing this switching.I don't want to just jumper over them and find that was the wrong thing to do and blow the rest of my stereo out.If I did this right, there should be two pics attached, one of the wheels and their markings and one of the "IC's" on the cover.I put a meter on the "IC's" and get open for ohms, tried running a magnetic screwdriver over them no change, but then if they are blown they would still be open anyway. Likewise shining an LED on them had no affect. But then I suppose they are looking to have current going to them to work - I'm obviously at a loss.Thoughts and ideas appreciated.

author: Paul Price
author_rank: Super Contributor
timestamp: October 04, 2014, 01:48:05 am
content: If the sensors you describe have a black plastic cover, it is likely they operated on infrared light and pass infrared light like clear glass while blocking most visible light. They work by sensing the clear leader at the beginning and end of the tap that allows the infrared light to pass through it. A small piece of plastic black tape over their lens will stop the reversing action.

author: goingjag
author_rank: Contributor
timestamp: October 04, 2014, 01:57:57 am
content: Thanks for the reply Paul, however the sensors are not located on the tape side of the mechanism so are not looking at the tape leader.They are on the underside with all the mechanicals and are "watching" the wheels go around, sensing the changes from black to silver, or possibly magnetic to non magnetic.I screwed up the attachment last time so I'll try to attach the picture with the bottom of the wheels showing how they are marked for sensing.So when the sensors detect no movement as when you have a tight tape at the end of one side, it will switch sides, moving the heads and reversing direction.

author: goingjag
author_rank: Contributor
timestamp: October 04, 2014, 03:13:04 am
content: Update, it is an optical arrangement. I was measuring at very low ohms on my first attempt.Bumped it up to 2000k scale and had a reading of nearly 400 ohms in ambient light. Took a high powered led and brought it up to it and it dropped all the way down to 20 ohms.So I'm guessing the light supply side (maybe sides) is/are not working since the spindles with the markings are turning fine.I'm guessing this would make it seem like the wheels have stopped on the black segment which would not reflect light, and therefore stop the receiver from conducting.So would it be safe to just jumper around the receiver making a steady path, or is it possible it is looking for the pulsing?Okay, I've confused myself enough for now.

author: David_AVD
author_rank: Super Contributor
timestamp: October 04, 2014, 03:18:26 am
content: It's looking for a pulsing signal. When it gets stuck high or low it triggers the auto reverse.

author: goingjag
author_rank: Contributor
timestamp: October 04, 2014, 04:22:07 am
content: Thanks David, makes sense.I'm having a hard time locating a pair with that form factor. I suppose I could wire an always on led in there to see if the sources are in fact bad. They read like a diode on my meter so that isn't even a given.I suppose it could even be the receiving latch that is bad, and trying to trace that out is beyond the scope of what I'm willing to try.So I think if an always on led doesn't fix it, I'll throw in the towel.Thanks again.

author: David_AVD
author_rank: Super Contributor
timestamp: October 04, 2014, 04:57:49 am
content: Is the supply spindle (non driven whichever the direction) really moving when the fault occurs?

author: SeanB
author_rank: Super Contributor
timestamp: October 04, 2014, 05:08:00 am
content: Easy to test the led by using a cellphone camera to look at it with 12V applied to the deck. Otherwise just use the diode test function on your meter and you will see on the cellphone camera the led glowing blue. Forward voltage drop will be around 1V2.Those rarely fail, the most common fault is the leads get dry joints or the pulse sensor input has a dry joint, shorted capacitor or an open resistor on the way to the microcontroller.

author: goingjag
author_rank: Contributor
timestamp: October 04, 2014, 07:05:57 am
content: The spindles were definitely turning when the fault occurs, as I had it on my lap watching with top removed.Unfortunately because the sensors are underneath the mechanism there is no way to apply 12 volts at the normal input and observe them, I'd have to try to figure out an appropriate place to apply voltage.I should be able to try the meter trick though, and I'll reheat solder joints in the circuit.Thanks.

author: David_AVD
author_rank: Super Contributor
timestamp: October 04, 2014, 11:37:21 am
content: Occasionally you get IR sensors where the LED emission drops off or the photo-transistor goes blind. Cracked joints is the other main thing to check.

author: goingjag
author_rank: Contributor
timestamp: October 04, 2014, 02:36:43 pm
content: Thanks David.After I check the led with my meter, I'll get out the soldering station and hit a few spots that might have gone cold and check the traces at the same time.

author: SeanB
author_rank: Super Contributor
timestamp: October 04, 2014, 03:13:47 pm
content: Best is to solder on 2 test leads to the sensor outputs on the main board, then put the kit back enough to get the casette deck running and use a scope to check for pulses on the lines, with a voltage that is close to 0V at low and close to most likely 5v at high. That then either exonerates the sensors or not. If it is there then the fault is on the main board with the cassette logic, likely a leaky capacitor or such.

author: goingjag
author_rank: Contributor
timestamp: October 05, 2014, 04:18:23 am
content: Thanks Sean B. but I don't own a scope (mainly because I never learned to use one). I may be able to see it with my logic probe, I'll have to check what voltage it looks for, or maybe use my analog meter if it's too fast for my digital meter.I did check the LED's with my meter set on diode and they do light up.I touched up the solder on all 8 leads, although they are surface mount not through hole and none of them looked cold to begin with.Reassembled and tested with the same result.Something I had not noted before, after roughly 5 attempts to play it actually stops trying but doesn't eject the tape. It sits idle without spinning the reels.I forced it to change to side 2 by putting the tape in with just a small amount of lead left. When it switched to side 2 it appears to attempt to play and then doesn't spin the reels. All of that may just be the logic of the way it should work if it doesn't get the pulses.This gives me the vague impression that some parts of the circuit that counts the pulses is working since it's sending signals to move the head away and try to rewind a bit and try again.Even though the LED's are functioning, they may not be getting power to begin with so I think I'll take your suggestion to solder leads on the output but I'll also put lead on the input to be sure I'm getting voltage in to begin with.Thanks again for the suggestions.

author: mzacharias
author_rank: Frequent Contributor
timestamp: October 05, 2014, 05:08:30 am
content: I know you said the reels were turning - but this is a classic "bad belt" problem.

author: G7PSK
author_rank: Super Contributor
timestamp: October 05, 2014, 07:23:40 am
content: As you want to use the tape deck with one of those units for connecting an MP3 player you could just disconnect the drive motor, I did this some years ago with the tape deck in the van I had at the time as when I used the MP3 player I could hear the motor noise on the speakers all those units are is a tape cassette with a tape head inside driven by the MP3 player which magnetically couples to the tape head in the deck unit.

author: goingjag
author_rank: Contributor
timestamp: October 06, 2014, 02:21:45 am
content: mzacharias, although I was 100 percent sure the reels were turning properly, I changed the belt anyway just to verify. No change. FYI I don't think I stated it, but the tape I have plays fine for 4 seconds, no warble or slow sound with the old belt nor with the new one.G7psk, thanks for the idea, but I don't think it will work with this auto-reversing deck, as it appears to cut out the sound when the reels are not spinning. I believe when I tried it by removing the belt entirely, I accomplished the same as disconnecting the motor. The end result was a no sound condition, but I'll probably double check that since I'm running out of ideas.I did put leads on various points to take voltage measurements while the deck is installed. I believe I created a short condition on one of them as I ended up with the reels not spinning and no sounds. As soon as I removed the 8 leads I had soldered in, it went back to the previous antics of starting for 4 seconds then stopping.I also confirmed that it will not play on side 2. If I put a tape in that is at the end of side 1, it switches to side 2 for a few seconds then switches back to side 1, tries a short rewind and play of side 1 for I think it was 3 tries, then ejects the tape. If I flip the tape over it will play as side 1 for 4 seconds disengage the heads do a short rewind reengage the heads and play side 1 for 4 seconds. It repeats this a varying amount of times, I've had it go 3 times then eject and other times had it go for what seemed like maybe 3 minutes without ever ejecting the tape, just playing 4 second bursts.I was seeing roughly 1.5 volts on the led's That is somewhat in question given the short I was creating on one of the other wires. I had soldered wires on various switches to be certain I was getting voltage which I was on two of the 3 small switches. I suspect the 3rd one was the one I was creating a short on. I tested all of those switches with an ohm meter and they all function well.So I'm going to go in and only solder leads to the led's and the optic receivers and see what I get. If nothing conclusive, I'll probably fool with powering off the drive motor which is separate from the load motor.Thanks all for the input.

author: goingjag
author_rank: Contributor
timestamp: October 06, 2014, 05:23:33 am
content: Well I changed my mind and decided to try disabling the drive motor first by removing supply voltage.As I feared, this just immediately kicked in the reversing logic and it just went back and forth between Side 1 and Side 2 without playing anything through the heads then ejected the cassette.As I was getting ready to solder test leads on the led/opto pairs I came up with the brainstorm of swapping them to see if that made side 2 act the same way as side 1 and vice versa.No such luck. swapping them had no affect.Then I decided to apply voltage constantly to the reel drive motor. This simply resulted in the tape continuing to move forward while the head disengaged for the reversing process, so when it reengaged for the next 4 seconds the tape had moved further along in the song.By the way I did eyeball all the electrolytic caps, and none have the typical bulge of a failing cap. Someone had mentioned that and I forgot to respond to it.At this point without a schematic, I think I'm whipped.Thanks again to all who tried to help.