The new-old-stock Casio W-115 AM/FM cassette player I bought online arrived this morning. The radio sounds great, and all the cassette functions work. I opened it to inspect its innards, and to hose contact cleaner around. The belts look fine. After running a tape for a couple of hours, the "wow" has settled out, and the mechanism is running smoothly. But it's too fast. I cannot seem to find the adjustment screw (I assume its a screw). There's no service manual for this online, and Casio Customer Support claims they don't have it, either. Can anyone please advise? I bet somebody here knows where to point me.
There is very little information online for this unit... it seems pretty obscure. I think the best thing to do in this case would be to take some pictures of the inside so we can help identify where a potentiometer (or adjustment screw) is located. Sometimes, it's on the main board inside, other times, it's on the backside of the motor. In more rare cases, there is not an adjustment screw, but rather it is a predefined set speed based on a circuit that cannot be adjusted. I'd say there is a pot in there somewhere... just post some photos to this thread, and we can identify where it is... If you look at the back of the W-115, you can see two holes near the top of the belt clip... I'm curious if this is where the adjustment would be... a lot of times, speed adjustment pots can be accessed without taking the unit apart, so I'd investigate this closer. In any case, look around the unit for anymore suspicious holes... these plastic models especially usually have an opening to stick a screwdriver in to adjust the speed.
Here's a look at the motor from a couple of different angles. It's the round object just peeking out at the right-hand side. That's literally as far as the lid is designed to open, by the way. Very narrow. Anyway, there are a couple of screws in there, next to the motor, that may be suspicious.
These are pictures taken while I was cleaning the PCB. This unit seems to have spent decades in Grandma's attic in South Carolina, feeling hot and humid. I tried lifting the circuit board, but it's tight and fast to the chassis, and it feels like I'm going to break it if I keep prying. There's sufficient access without removing it to give all the goodies on the other side a good contact cleaner bath and blow-out with compressed air. I can eye-ball the bands well enough to see that they're sound. It's just hard to get a photo. The tape motor is on the opposite side of the "close-up" picture.
Yep, one of these three is your guy. It also seems that the bottom two lineup with the holes on the outside of the case?? My guess is that one of those pots is for the speed, the other two are for L/R playback gain. That is a common arrangement for a portable tape player. The 4 smaller brass screws arranged in a diamond on the other end of the board adjusts the tuner for the radio. Here's your options: 1. I would trace the circuit path from each of the pots (the pots are the holes with the flat blade screw driver adjustment I circled) through the traces to see if any of them end up near where the motor wires connect in. Each pot has two solder joints one side of it, and one on the other. The pot that is nearest to the motor wires may not automatically be the speed adjustment, but tracing where the green printed wires go from the motor wires or back from one of those pots should give you a good idea. (You are doing all of this because you have no service manual) You can also check for voltage at the motor, then try to follow that voltage through the circuit to one of those pots... (you need a multimeter for this) ... You need to do this while the unit is on and the motor is spinning. Also, type in any numbers on the IC chips to google to see if you can identify a motor driver chip around the place you can trace from. 2. Just start turning. I don't mean this recklessly, I mean you should carefully do this with precision... taking a close up picture of each pot, then using a small flat blade screw driver, ever so gently nudge each one and see if the speed changes while listening. Remember if it doesn't change anything, or it changes something undesired, turn them back to where they match the reference photo or marking you made. 3. Replace the belts and see if the speed fixes itself. Those belts even if they are sound, they will undoubtedly stretched over the years at least a little, so that can Make the speed change. Replacing the belts may rectify the issue without the need for any other intervention. Here's what the pinout of a potentiometer looks like: On pin 1, you will have a supply voltage, probably whatever is coming out of a regulator nearby. This is a common voltage you would measure throughout the circuit. Pin 2 is your output voltage going to the motor (lower voltage than supply). Pin 3 is your ground. As you adjust the trimmer pot, pin2's voltage will change, making the motor speed up or get slower. To check a pot, just place the ground (black wire) of your multimeter on to pin 3 (ground), then the red lead onto pin 1 and 2. Set your multimeter on DC volt mode at around 20v. Hope this helps!
What I recommend doing before adjusting is take a measurement of the resistance between the cursor of the trimpot and one end. This way it can be readjusted to what it was before very easily. Looking just at the back of the PCB it's unclear which of the 3 trimpots is the tape speed adjustment one. While indeed it would seem logical that 2 of them are for playback gain and one for tape speed, that may or may not be the case. Playback gain adjustment is typically found only on units that have Dolby noise reduction because Dolby is senstitive to level and there needs to be a clear correlation between magnetic fluxivity on the tape and voltage levels. The speed trimpot is close to this motor governor circuit, but do keep it mind this can be a dedicated IC (typically a small one like 8pin), can be integrated into the pre-power amp or it can be made with discrete transistors. EDIT: A qucik search for the KA22136 IC reveals this is the pre-power amp with integrated motor governor. Speed trimpot looks to be the middle one, the one closest to this SMD IC.
That seems helpful. Thank you. I'm waiting on some De-Oxit to arrive before I mess with this one again. (The crud visible on the PCB is just not yielding to plain old CRC.) When that arrives, maybe it will loosen up the stuck-on circuit board. And maybe then I can move on to the problem (grounding issue?) causing the terrible buzzing when the unit is playing in the "A direction". Doesn't happen when it's playing in the "B direction" (auto-reverse). And this one arrived NIB !
