Big Ben deck playback too fast
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Waaay back, I asked about reconciling the resistance issue because it is THE step we need to address in order to confirm if the problem is in the circuit or in the motor.
NOW that we go that out of the way, we can safely conclude that the problem is within that motor. It runs fast so the motor mechanicals and brushes, etc. seems all in good working order. The problem is in the internal speed control circuit board. Once you get that back cover open, you will likely see a small PCB (I bet it's the same one with extension that protrudes from the side where the wires connect to). There will be a handful of components on it and a IC. Since the service manual does not provide the internal circuitry schematic (owing to that these were usually replaced as an assembly when they were available), your best bet is to find the IC and check the datasheet on it. The datasheet usually includes a sample circuit diagram which will likely match up quite closely to what you have in there. You already know how to do component testing so if the issue is not in the individual components, it's likely the IC. An example of some are: AN6650 /51 /52.
On most cassette motors, the back cover is held on by several crimps. However, the method differs depending upon the motor. If you want to split the motor bad enough, I'm sure you can do it. Good luck.
NOW that we go that out of the way, we can safely conclude that the problem is within that motor. It runs fast so the motor mechanicals and brushes, etc. seems all in good working order. The problem is in the internal speed control circuit board. Once you get that back cover open, you will likely see a small PCB (I bet it's the same one with extension that protrudes from the side where the wires connect to). There will be a handful of components on it and a IC. Since the service manual does not provide the internal circuitry schematic (owing to that these were usually replaced as an assembly when they were available), your best bet is to find the IC and check the datasheet on it. The datasheet usually includes a sample circuit diagram which will likely match up quite closely to what you have in there. You already know how to do component testing so if the issue is not in the individual components, it's likely the IC. An example of some are: AN6650 /51 /52.
On most cassette motors, the back cover is held on by several crimps. However, the method differs depending upon the motor. If you want to split the motor bad enough, I'm sure you can do it. Good luck.
BoomboxLover48
Boomus Fidelis
If you look close, I think you can see a small gap at the seam where the back plate is. You may be able to tap it out with a tiny drift or carefully placed screw driver. Or cut a few kerfs with a dremel and then spread the tangs to free the back plate. It's definitely not welded right? Anyhow, I'm sure you can do it if you are brave enough. After all, what have you got to lose? A deck that runs at double speed is not good for playing cassettes anyhow unless all you want is to use it as a tape FF or RW tool.
Oh and the way that the front end looks, it's clear that all the innards are populated through that rear cover. My guess is that it's merely a cap that's tapped in (inteference fit) until it bottoms out against an internal stop.
Oh and the way that the front end looks, it's clear that all the innards are populated through that rear cover. My guess is that it's merely a cap that's tapped in (inteference fit) until it bottoms out against an internal stop.
BoomboxLover48
Boomus Fidelis
The flint stones method is as follows:
I would slip a screw driver tip barely in the speed adjustment hole, and lever/pry on the edges and pry it. See if the back plate comes off.
Rotate and gently warm the sides all around and then try the same.
I would slip a screw driver tip barely in the speed adjustment hole, and lever/pry on the edges and pry it. See if the back plate comes off.
Rotate and gently warm the sides all around and then try the same.
BoomboxLover48
Boomus Fidelis
BoomboxLover48
Boomus Fidelis
motor with bipolar totem pole MOSFET...?
that variable resistor adjustment might work...
may be the bearing cleaning might save..
that variable resistor adjustment might work...
may be the bearing cleaning might save..
The last Sanyo I worked on (MX-720) had a motor that would run too fast even after adjusting the pot. Turned out the pot just needed some contact cleaner to restore functionality.
BoomboxLover48
Boomus Fidelis
For testing, sure. Or better yet, parallel a couple of 100R resistors and you should be good to go.
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