This may well be a long thread but I hope at the end of it, I will have a working unit and an A-Z of fault finding & repairing one of these will exist for others to read. 

From the beginning, I got this deck in an unknown state clearly not working due to no tacho and no cartridge. These along with the service manual have been obtained and all the electrolytic caps have been replaced except the big 2200uF 40V one which tests OK (waiting for a new one)  and the non electrolytic in the transformer case which measures exactly 39uF.

Usually at this stage I understand the machine would often work if the gremlins had not got at it. Not this one!

Switching on (without the cartridge in place to protect it) a red dot appears in the  display. Pressing 'turn' makes the deck go round, either of the speed selectors works the display changes 33/45  and the turntable rotates  accordingly. Pressing 'play' the arms move, I can see a red dot on the end of the detector arm whilst it is moving and there is a light shining under the detector arm. It does not make it to the record, it just stops by the end of the 'stick on' aluminium surround but the turntable keeps rotating. The 'stop' button does not seem to do anything nor any of the other buttons in this condition.

Any clues on where to look from here would help.

Q1 what makes the pickup arm raise & lower? there is nothing obvious on this one.. 

Q2 If it was working correctly and there was no record, what happens when 'play' is pressed? would the detector keep going until it got to the centre then return & switch off?. presumably this is how it would find a 7" record? by seeking it??  

Thanks for your help

Something preventing the carriage from moving fra enough. After a record is sensed, the speed is reduced and this is where problems often show. Probably accumulated dirt on the long threaded servo motor spindle or the servo motor belt slipping.

Q2. Exactly.

Martin

I have wound the threaded rod by hand from one end to the other.  There is no obstruction or sticking. The belt could be slipping but I don't think so. When it moves, it is very positive and always the same amount. I will check.

The detector arm does not get as far as the record/turntable, It moves 2-3 cm from 'home' then stops about 1/2 cm from the record. The red light at the end of the detector then goes out. In correct operation it must surely go past the record by 1-2cm?? before the pickup arm drops. Should the red light stay on whilst 'detecting'??

How does it know a record is there? colour?  or reflection from the detector arm (up & down) or a pre set turns from rest? If so how is this set?

Does it matter the pickup is removed?

Thanks

PWH

I find the LED by the transverse arm motor ? pulse counter? is open circuit part no 8330056 Anyone know what its replacement is?

The record is detected by reflection but the sensor arm obviously has to be over a record to sense one. If it doesn't make it to the record, check for bad solders. Especially in the power supply / rectifier diodes areas and at the connectors along the edge of the main board.

Replace capacitors. Make sure to get them all done, a kit is available.

Martin

Hi Martin, I have taken your advice as in the previous thread.

More investigation shows that when the 'play' button is pressed and the microswitch under the deck is held in the 'home' position the arms travel the length of the carraige so no belt slip or obstruction.(will not return though)  Also, there is a small voltage across where the dead LED sits, so it should be on.

I suspect that when 'play' is pressed some pre set number of turns is allowed by the uP after which it expects pulses from the counter. As the LED is out, it sees nothing, counts no pulses, so goes nowhere.  I will stop until I have fixed this LED first, which I need to identify, as per prevoius post then obtain. It has a small 'lens' on it.  May not be the exact cause but it must help the repair process.

Thanks again for your help.   

The LED and the sensor lamp are two different things.

Check the adjustments for the << and >> buttons and check the optos at the end of the threaded spindle.

Martin

The << >> buttons do nothing at the moment.

The LED I am describing is part of an assembly which has 2 detectors as well on a little PCB  by the motor for the arms, I think you are describing them as 'optos at the end of the threaded spindle'.

When the motor turns, a cut out cylinder interrupts the light . Obviously if the LED is not working then the receivers are not detecting. This is the broken part I am trying to identify. Could be an Infra Red LED?

Thanks Peter

An IR-LED exactly !

You can check it using a digital camera (cellphone camera). 

Martin

The IR LED is definitely broken. What is a suitable replacement part please?

I repaired one using an IR LED from a computer mouse of the old type with the rubber ball and 2 optos.

Martin

The original LED is back in place and in 'play mode' with the arm stuck as far as it will go,, I rotate the counter cam and it pulses the optodetectors about 11-0, 11-0 volts as it is turned on both. so I am happy the OPE1 parts work. I now need to work out what makes the arm move then stop short of the record because you won't get any pulses unless the motor is turning the cam.

I take it the top centre of the diagram is the motor for the arms (OM1) and not the turntable??

All suggestions welcome 

On the underside of the uP enclosure there is a screened wire. The inner goes to pin 15 of the uP

where does the sceen go? mine is not connected. Pin 12 would be a good candidate but I woud like to be sure

Are you sure you replaced ALL the caps ? There's one inside the CPU casing too that most people miss. It's a quite important component and often bad, sometimes even disintegrated.

The carriage home sensor is not misadjusted ?

Martin

Dillen wrote>There's one inside the CPU casing

Yes on the component side, one side is not connected via PCB, just used to secure it? I replaced it. looks a bad bit of design.

Dillen wrote >The carriage home sensor is not misadjusted ?

Is that the microswitch with a long metal part called the SO switch? 

The manual is not clear on this

It says 'activate play '~notice the correct set down position of the pick up (146.3 -148.25mm from record centre) Loosen screw B and move the switch to compensate for misplaced set down' 

It does not say whether the switch should be on or off.

Thanks & Regards

PWH

One more observation, when in 'play' and the arms have moved 2-3 cm from home and stopped, if you turn the belt connected to the arm motor,the LED at the end of the sensor arm flashes so really confirms the IR  counter LED is working.

How can I tell if the sensor arm is giving an output? There is a light shining down from it. 

Thanks