Sansui cp-f7 deck issue

Before and after rebelt, even though all functions work as they should, the deck auto stops after a second or two. I’ve cleaned and regreased the mechanism in the back with the leaf switch and levers but it doesn’t seem related to that. The tape sensor switch works fine. All new belts.
Beginning to think it may not be mechanical, any ideas anyone?

Does this deck have any idlers that need cleaning Dave

I dont believe so, it looks to be fully geared and is logic controlled.

damn

I only had one box do this Dave, a Sony, i replaced the tape counter belt as it had a play sensor and all was well. May not be that but worth a shot even just to eliminate it as a possibility.

this maybe the case, the m90 is the same

All belts replaced, no dice.
I cant see any hal sensor on the exploded diagram.

I know this deck pretty well now, physically everything seems good.
If someone could look at the freely available schematic and help point me at an area to test which could cause the auto stop please.
I’ve also noticed that if I press pause right after pressing play, the same thing happens with stopping the deck and the pause does not make it pause but stops it as it does by auto stopping. Could this point at the main logic ic?

I don't see anything in the deck diagram or schematic that shows a play sensor, I don't even see an oldschool tension lever.

Might be something that senses when the motor is running but can't turn anymore when it's at the end of the tape?

There is a hall effect sensor, it is on a magnet and runs off the counter. If the sensor doesn't detect movement, it will shut off the deck after a second or two.

This deck has 3 motors... one to drive the mechanism, one to run the reel motors and a third for the capstan. I won't be one bit surprised if one of them is not turning, especially the last 2 motors.

Thanks guys, the deck with 3 motors is different to mine as it only has one motor but is still labelled cp-f7.
I did take a look at the counter which has a magnet around the inside of the wheel but there doesn’t appear to be a sensor, at least not mounted near it anyway.
There is another service manual which has the right single motor deck schematic and though I have looked through it at length, I couldn’t find a sensor. On the tiny pcb near it is a voltage regulator dm106 and nothing else. Could this be acting as a sensor? it is closest thing to the magnet.

Yes, DM106 is the magnetic sensor. It is not a voltage regulator.

Thanks Norm, i’ll order a replacement.

Wondering if it is possible to bypass this kind of sensor, even for testing purposes?
I have a replacement incoming but it could take some time.

Replaced dm106 with an equivalent, 78L08, sadly same issue but with a difference being that if I hold finger on play/ff/rew it stays in position and works which it did not do before. Release finger and deck stops.
Seems to be a positive 3 terminal voltage regulator +8v, 100mA according to datasheets and equivalent options.

docs said:

Wondering if it is possible to bypass this kind of sensor, even for testing purposes?
I have a replacement incoming but it could take some time.

Click to expand...

Hall effect sensors provide an output based on magnetic strength, so it's reasonable to conclude that the output from a properly working sensor, mimicking a rotating magnet would be some form of pulse, perhaps a square wave. However, I can't begin to tell you what the expected output strength would be. If you look at page 33 of the SM, it specifically says it is the magnetic sensor board.

docs said:

Replaced dm106 with an equivalent, 78L08, sadly same issue but with a difference being that if I hold finger on play/ff/rew it stays in position and works which it did not do before. Release finger and deck stops.
Seems to be a positive 3 terminal voltage regulator +8v, 100mA according to datasheets and equivalent options.

Click to expand...

First off, it makes no sense that the item would cross to an 8V regulator. How and why do you think that the hall effect sensor is a voltage regulator? If you don't know the history of the boombox, you can't make that assumption that whatever component in there is a voltage regulator, IC, transistor, or what have you. You should go by the service manual. Secondly, if you look at how that device in used in the circuit, it is powered by an 5V rail, one leg to ground, and the sensor leg driving a transistor. There is 0.0% chance that an 8V regulator is intended to work with those circuitry complements. If the 3 leg'd item in there is currently a voltage regulator, someone in the past could have replaced the original hall effect sensor with one thinking that it "looks" about right. But then again, it could be any opto sensor, transistor, or any IC with 3 legs... Now, if you are going to cross the original sensor and can't find an exact match, I would say that it's probably better to try and find another hall effect sensor to try rather than stuff a completely improper component in there. IC voltage regulators are commonly used in virtually all electronic devices today. However, back in the era that this boombox was produced, the prevailing form of regulator circuit is the common collector transistor zener diode regulators, and this should have been sort of a clue regarding whether a VR belonged in that spot.

Pretty sure the component was original. It is marked dm106 and googling that refers to nte981 as an equivalent along with about 15 others. All of them say theyre a voltage regulator but ofcourse I’m not certain as I can’t find datasheets for dm106.

How about test the original dm106 and see if it’s working? 5v, ground, and 1 sensor lead. See if sensor leads responds in the presence of magnetic field to the device.

https://uk.farnell.com/c/semiconductors-ics/ic-sensors/hall-effect-sensors

If you study the circuit diagram, you’ll see that of the 3 pins, one gets 5v, another goes to ground and the last drives the transistor. This indicates that the sensor is intended to work with a 5v supply. I would check farnells inventory and find one that works at 5v and ideally is pin compatible so no leads needs to be crossed in weird ways.

Thanks Norm, will order one and see where we go.

Tried a A1104 I found, same. Guessing its out of range. Will try another rated at 5v.

Norm, I can get any of these, which do you think is best match please?

https://cpc.farnell.com/webapp/wcs/stores/servlet/AjaxOrderItemDisplayView?catalogId=15002&langId=69&storeId=10180&krypto=ABwoyiQMnuI%2FngE1DWdBdpO4dqVa2E%2FLq7qoDX2ZtW5UEvhn6T0pbp33BdmFINKczN7B12UIl27u1S7frLKUQfwG%2FjljeCxmcfOD6oSwf5gYLTlQPHmxf0WU34YAcNii1p%2BJYUPvr9tONONy9XvJEH2SWWcyY3VONqUxYkpGINkqNqiXRj1UniLgNkbRWTHC&ddkey=https%3AOrderCalculate