At least we have made one more step towards it working. Can you clarify a few points.
When you press play does the play light always come but its only sometimes it actually plays ?
When it stops playing is the stop LED or pause LED on (Or are all LEDs off.) ?
On the left hand side of the schematic for U301 pin 24 goes to two sets of contacts one labelled 0-Stop and the other counter 000. I assume the counter one is to set it to stop at a particular place on the tape. If this is the case are you sure this is not the reason for it stopping ?
I don't think the pressure solenoid should operate straight away. I think the capstan is always rotating then the tape would start to move as soon as the unit was switched on.
You could try wind and rewind to see they continued to the end of the tape or they also stopped at random.

Les.

 

At least we have made one more step towards it working. Can you clarify a few points.
When you press play does the play light always come but its only sometimes it actually plays ?

Yes all of the LED’s are working now; except pause, I need play to work first before I can test pause, play doesn’t work now.

When it stops playing is the stop LED or pause LED on (Or are all LEDs off.) ?

I have been taking voltage readings most of the afternoon; as this seems to be the way to diagnose, I can now confirm playing mode still does not work at all, motor 2 works, it must of been nearly right when it did work earlier when I said it sometimes works, now it doesn’t.
The play LED does work every time I press play for a few seconds only, maybe till motor 2 stops at the same time.

On the left hand side of the schematic for U301 pin 24 goes to two sets of contacts one labelled 0-Stop and the other counter 000. I assume the counter one is to set it to stop at a particular place on the tape. If this is the case are you sure this is not the reason for it stopping ?

Yes the counter is freely working and the memory stop isn’t activated. If you wanted to replay from a specific place on the tape; you would press memory stop and then at the end of the tape it would automatically rewind to that point, then play.

I don't think the pressure solenoid should operate straight away. I think the capstan is always rotating then the tape would start to move as soon as the unit was switched on.
You could try wind and rewind to see they continued to the end of the tape or they also stopped at random.

Yes I agree with you wholly about the pressure roller solenoid coming in only after play is pressed.

Fast forward and rewind only works for 7 seconds precisely, another eye-opener, the LED’s are working, even stop, when it stops?

IC427 pin 11

IC432 pins 5 and 10 these voltage stand out as a non-logic value.

I have started a fresh with my readings, as IC433 has been renewed.

 

Hi Michael,
Can you go through the play flow chart again filling in all the values from it in the table from post #122. Can you also include IC437 pins 12 &13 and IC430 pins 1 & 2.
The voltage readings on IC427 pin 11 and IC432 pins 5 & 10 are close enough to - 11 volts or 0.0 volts to be considered valid logic levels. (I have not gone through the logic to see if they are the correct logic states.)

Les.

 

Hi Michael,
Some more questions occurred to me overnight.
1 When it worked on play for about 10 seconds did it sound as if it was running at the correct speed ?
2 Now when you press play does the play LED stay on or does it go out after about 10 seconds. ? Also is the tape moving but no sound is produced ? Can you see if the capstan is revolving and if the pressure roller is pressing the tape against the capstan ?
3 When it is in the wind and rewind state are both reels in the cassette revolving ?

Les.

 

1 When it worked on play for about 10 seconds did it sound as if it was running at the correct speed ?

I suspect that play was running at the correct speed because the pressure roller solenoid; it didn’t come across for a few seconds and then it came across and I saw the tape going around, to hear the sound I would of needed the headphones plugging in and I didn’t notice the VU meters working, as I was watching the gears in play mode.

2 Now when you press play does the play LED stay on or does it go out after about 10 seconds. ? Also is the tape moving but no sound is produced ? Can you see if the capstan is revolving and if the pressure roller is pressing the tape against the capstan ?

The play LED only stays on for 1 second the same time as motor 2; have to keep play pressed to keep the LED on whilst getting the voltage reading.

No the tape does not move at all, whilst pressing play, I open the cassette door and yes the capstan motor is on, rotating the rod, ready and waiting for the pressure roller to come across. The pressure roller solenoid is the only means of swinging the roller across in to position.

3 When it is in the wind and rewind state are both reels in the cassette revolving ?

Yes both reals are working together when pressing wind or rewind.

Have uploaded the voltage results requested in post #123 and have added user instructions into my OneDrive and a Hi-Fi review for you; many thanks for all your help.
https://1drv.ms/f/s!AuQDAPiShOjc9RoD2G3xlbzfvUuQ

 

Hi Michael,
You have not filled in the results to the end of the play flowchart. It does not seem to go past IC433d (Pin11).
Can you add these results to the table that you posted in post #125

Les.

 

Here we are; unless there is a logic reading where there should be a different logic reading all looks normal?

 

It looks like IC437d is faulty. Replace IC437. When you shorted out something that destroyed the voltage regulator was it on board U301 ? THe output of IC433d feeds one of the inputs to IC437d so I'm wondering if the short caused these faults.

Les.

 

It was the four transistors that caused the initial fault of not being able to play, the transistor would of amplified excessive voltage, wouldn't it?

 

Have now replaced on the logic control board U301; IC430, IC433, IC436, IC437, this includes the two solder repaired IC’s. Play works continuously without stopping; Pause and it’s LED are working, we are slowly winning.

Fast; forward and rewind works for 9 seconds precisely and then goes to stop showing that LED light, there is no sound coming through the headphones, the VU meters are working.

I wonder if you can identify any more readings that are showing High State (-0v); that should be Low State (-12v) values from the table of voltages in post #127?

I have identified some none logic voltage readings relating to the manual’s voltage readings, this is a repeat for me because in the past I had no sound on the left outputs and the VU meters were working, you can see these in the uploaded file called N5748 No Sound. Can this be another faulty IC on the logic board?

I think I need to print another table to record more reading; can you kindly give me some more flow chart readings to acquire, for the fast forward and rewind, thank you?

 

I think board U301 is now working as it should. I think wind and rewind are stopping due to some fault condition being detected.

For the wind rewind fault do the following tests. Test the voltage ACROSS (NOT with respect to ground.) the wind motor (M2) terminals and note the values. Monitor these voltages for the full time it is winding and rewinding to see if it changes. Also check this voltage in play mode.
Monitor the voltage with respect to ground on pin 1 of IC455 for the full duration of wind and rewind.
It might be easier to monitor the motor voltage between TS451 collector and TS453 collector.
Check that the pressure roller is not pressing the tape against the capstan in wind and rewind.

For the no audio out problem do the following. Connect an amplifier to the line out to check if you can hear any sound from them. If you can then note if it seems to be playing at the correct speed. On board U410 check the voltage with respect to ground on pin 6 or 7 of IC426 an IC427

Do you have any kind of audio signal generator ?

Les.

 

For the wind rewind fault do the following tests. Test the voltage ACROSS (NOT with respect to ground.) the wind motor (M2) terminals and note the values. Monitor these voltages for the full time it is winding and rewinding to see if it changes. Also check this voltage in play mode.

TS451 C (+) and TS453 C (-) these are the connections.
Unit on, 0mv. Play, -3.57v. Wind, -6.7v to -6.9v. Rewind, 7.4v to 7.9v.
The pressure roller solenoid was deactivated during wind and rewind, meaning roller was clear from the capstan.

Monitor the voltage with respect to ground on pin 1 of IC455 for the full duration of wind and rewind.
It might be easier to monitor the motor voltage between TS451 collector and TS453 collector.
Check that the pressure roller is not pressing the tape against the capstan in wind and rewind.

Unit on, -11.25v.
Wind, -11.2v to -11.1v.
Rewind, -11.0v to -10.9v.

For the no audio out problem do the following. Connect an amplifier to the line out to check if you can hear any sound from them. If you can then note if it seems to be playing at the correct speed. On board U410 check the voltage with respect to ground on pin 6 or 7 of IC426 an IC427

Do you have any kind of audio signal generator ?

All four pins give the same voltage to ground, 15v.
Unable to connect to the amplifier, sorry.
Have no audio signal generator, sorry.

 

Can you go ALL the way through the play flow chart both in the stopped state and the play state. (You can miss the path down through TS465 to the play LED as we know that this is working. Also you can miss the board pins as these connect to the last IC pins in the chain.) I am particularly interested in IC427d output as the controls analogue switches in the audio path. Can you also check the voltage on pins 6 & 12 of IC427 on board U405 in both the play and stop states.
I have not yet worked out what may be causing wind and rewind to stop.

Les.

 

Can you go ALL the way through the play flow chart both in the stopped state and the play state. (You can miss the path down through TS465 to the play LED as we know that this is working.

Also you can miss the board pins as these connect to the last IC pins in the chain.)

Please can you explain more about this later part of the exclusion

 

The numbers in circles at the end of the flow chart are the numbers of the pins on the board that connect it to the backplane. (Item H on page 15 of the manual.) For example the output pin of IC427d connects to pin 34 on the board. (U301)

Here is the reasoning for suspecting that the audio path may be broken at IC427 c&d (One for each channel) on board U405. If you look at the schematic of this board then the audio must be getting to the input of the level indicator board (U407) The signal at this point also goes into the DNL (Dynamic noise limiter.) board U411. The output of that board goes to analogue switch IC U427 (sections c &d) The control signals on pins 6 & 12 originate from U427d on U301 (Via a level converter.)

Les.

 

Can you go ALL the way through the play flow chart both in the stopped state and the play state. (You can miss the path down through TS465 to the play LED as we know that this is working.

After pressing play; I now have to press stop, another achievement, thank you, see the uploaded PDF.

Also you can miss the board pins as these connect to the last IC pins in the chain.)

Thank you for giving me the explanation (in #135) understood.

I am particularly interested in IC427d output as the controls analogue switches in the audio path.

I hope you find something; there are some 5 and 10 voltages, now showing, that didn't show before?

Can you also check the voltage on pins 6 & 12 of IC427 on board U405 in both the play and stop states.

U405 Main Board; IC427 voltages to ground, first reading initial followed by SK14 play button pressed.

Pin 6. -4.68v and -4.1v
Pin 12. -4.68v and -4.1v

 

I think IC427 on board U301 is faulty. Before replacing it check the voltages with respect to ground on IC427 pin 14. (It should be close to zero volts.) and check the voltages with respect to ground on IC427 pin 7. (It should be close to -11 volts.) If these voltages are correct then replace that IC. If not report the results.

Les.

 

IC427 voltages to ground, first reading initial followed by SK14 play button pressed.
Pin 7. -21mv and -5v
Pin 14. -16m and -29m
Pin 7. is low, am I right, that pin 3 of IC436 has something to do with this lower voltage, as it is also a non logic voltage?

I have tested additional IC433 voltages to ground, first reading initial followed by SK14 play button pressed.
Pin 8. -17m and -11v
Pin 9. -60m and -30m
Pin 10. -11v and -30m

Edit: I have an error with a voltage; IC432 pin 2. Iv should be -10v ( pins 1 and 2 are connected on the rear side, so the voltages should have been the same, they are)

 

Pin 7 is the negative power supply pin on IC427. (The power connections are shown on IC427a at the top left hand corner of U301 schematic. This fault MAY also be causing wind and rewind to stop.) This is negative rail "B" which comes into the board on pin 28. With U301 removed measure the resistance between IC427 pin 7 and pin 28 in the board connector. It should be almost zero ohms. If not then there is a break in a track on the board. This path uses paths on both sides of the board which looks like they are joined at a plated through hole just above the left hand end of R564. (viewed from the component side.) If the resistance is near zero then the fault is between pin 28 of the connector on U304 and pin 11 on U402 via conn2 pin 2. You will have to trace this with resistance checks. (When you shorted something out you could have melted a track on a board.)

Les.

 

Did you see my edit in my last post #138 ?
Resistance values: Board U301, IC427 pin 7. To board pin 28, 0.3 ohms
U301 connection block, pin 28, to board U402 cable entry 11. on the component side 0.3 ohms.
Right through from IC427, pin 7. To cable entry 11, 0.5 ohms.
I think these are acceptable?