Philips N4520 Counter and Transport Problems

[tangoromeo]

I know that there are past threads regarding these 2 issues but having read through them I am none the wiser and I am unsure if the 2 problems are related.

My initial problem was that the counter did not count although it illuminated and indicated the correct speed. On a previous posting about this issue the IR emitter / receivers on the Opto board 2A were at fault. As in that thread I was also getting strange voltage readings across the IR emitter diodes so replaced the 2 units with compatible components. I also replaced the 2 other transistors on panel 2A TS283 and TS284. The voltages across the IR emitter diodes now both read approx 1.3V which I believe is OK.

On the previous thread this cured the counter issue but in my case it made no difference, the counter still did not count. But as in the previous thread, another fault then appeared where the transport will not stay engaged for more than a few seconds. The symptoms are identical in play, FF and REW where the relay on the control board 4B operates about a second after pressing the button and then the solenoids disengage. If I hold in the relevant transport button for a few seconds whilst the relay tries to operate then release it the transport sometimes continues, but not always. In any event the counter does not count.

Unfortunately I don't have a scope so am not sure how to confirm definitely that the Opto board is now working but I tried disconnecting the power from the Opto board and it made no difference to the transport problem so I assume that this is coincidentally a new fault which appeared after I replaced the components on the Opto board.

Another interesting issue is that my machine appears to be a later version than any of those shown in the Service Manual. I am using the German language Service Manual from HiFi Engine where, for instance, the latest version of the Opto board 2A is marked 3408.3. My board does not seem to have a similar marking but is marked ELIN P2 94V1. There are noticeable differences, eg my board has 7 input / output terminal whereas the manual version has 6. The PCB has a different layout although my knowledge of circuits is not good enough to know whether the differences are significant. I have attached a photo of my board to illustrate. Apologies for the messy soldering around the emitter/receiver terminals due to parts of the tracking and pads coming off with the old components. This has now been tidied up and checked for continuity and no shorts.

Similarly the Counter Board 5A seems to be a different version, the manual version having 7 input / output terminals and mine has 8. Again I have attached photo to illustrate.

So the issues are:-

1 How can I check the output of the Opto board without a scope?
2 With the regard to the non-counting counter is the next step to look at the IC / Transistors / Caps on counter board 5A or the control boards 4B / 4C and what would I be looking for?
3 With regard to the transport issue, I arum the issue lies in Control Boards 4B / 4C but again, where to start looking without wholesale replacement of components.

Any comments or suggestions gratefully received.


If I hold in the relevant transport button

[Sideband]

Just for the record, ELIN P2 94V1 relates to the material and fire rating of the PCB!

[tangoromeo]

Originally Posted by Sideband

Just for the record, ELIN P2 94V1 relates to the material and fire rating of the PCB!

Thanks for that!

I can't find another version reference printed on the PCB except for the word "Opto"

[tangoromeo]

Originally Posted by tangoromeo

Similarly the Counter Board 5A seems to be a different version, the manual version having 7 input / output terminals and mine has 8. Again I have attached photo to illustrate.

If anyone knows of a later version of the service manual than the one on HiFi Engine that would also be useful, thanks.

[Analogue man]

The reason the transport will not remain engaged is the same fault as the counter not working as a stationary counter acts as an end of tape cut out. Exactly what the solution is though I'm afraid I don't know.

[tangoromeo]

Originally Posted by Analogue man

The reason the transport will not remain engaged is the same fault as the counter not working as a stationary counter acts as an end of tape cut out. Exactly what the solution is though I'm afraid I don't know.

Thanks for that pointer Graham. I think I will concentrate next on the Counter board. I know there are instances of the IC on that board failing but I would have thought that would have resulted in no illumination whereas the counter does illuminate, so I will concentrate first on the capacitors and transistors.

One other interesting symptom is that if I "override" the auto stop by keeping the FF or REW button pressed for a few seconds, once I release the button the Winding Speed control does not function and the motor simply builds up to maximum speed. Not sure what the significance of this is.

Update on the version of the Opto Board, I did find a number printed on it which is 3103 203 3408.4 which must mean this is version 4 of the PCB whereas only versions 2 and 3 appear in the manual.