1974 Philips N1500: Finally!

Well my luck has run out, SK402 has now given up, this repair was so close to being a success as well  ? 

The internal prongs of SK402 that grab the slider and is operated when the play button is pushed, are likely broken or distorted through use. There is absolutely no way to work on it or see the internals of the slider prongs in situ. I'm not sure even if its removed from the board one can the open it or repair it in some way.

SK402 is the smaller of the two rectangular switches, the one on the bottom left of the photo

That leads to the next utter nightmare, the removal of SK402. To remove SK402 from panel 45 will require delving in under a rats nest of wires and then unsolder said rats nest of wires

SK401 pads are hidden under the rats nest of the wires at the top of the centre panel

I've carefully undone all the wire ties and splayed he various wires apart to reveal SK402's pads. I need to take plenty of photos and a video of the board at all angles so as to document the position of everything, there's a huge potential to screw up here.

SK402 pads revealed and the slider bar removed from SK402

Wish I could call CES and order up a new SK402,

Rather deflated I will now slope of to bed .............................................

After a sleepless night of my brain constantly working over the problem of how to fix SK402 , as first light broke I was up and back into the workshop.

I carefully mapped the top of SK402 with regards to fly-lead wire connections and then super carefully mapped the print-side rats nest wires. For good measure I took lots of photos and also filmed it so as to have a live multi-angle reference, just in case.

With patience and careful application of the soldering iron I have managed to remove SK402 from panel 45. It remains to be seen if I can get inside the switch ( very doubtful) or see if I can observe the problem within and rectify. I'm not holding out much hope and fear this is where the story of this N1500 will end, scuppered by one poxy switch!

If that is the case all I can hope is that a scrapper N1500 turns up somewhere or a spare panel 45 crops up to salvage a new SK402 from. Sod's law I have plenty of N1700 spares (well one scrapper for donor parts for my other two gooduns) but zilch! N1500, still lets see what I can do, fingers crossed!

p.s.
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Out of interest, it won’t help the problem, are there contacts on both sides of the sliding contact bar?

These are 'standard' Philips slider switches. Many times I've removed a slider, cleaned it and applied a light coat of switch cleaner and then reinserted the slider with complete success (did it on my Philips scope a few months ago). However I have never tried to get inside the contact section and re-tension any contacts. It certainly looks like the two end contacts (at least) could do with re-tensioning since when the slider is removed, opposing contacts usually touch (or very nearly). What you do with any nearer the middle section... ? I've never tried to separate the two nylon halves since if the switch was that far gone....replacements were available....If you can get it apart, re-tension the contacts and reassemble and reinsert the slider then at least there is a chance that it will work again. Hopefully it will work until you can find a good replacement...there must be one out there somewhere....!

Moving to the bench microscope I could see within the switch, as sods law would have it the middle contacts were badly bent. Absolutely no hope in hell of fixing it from outside, it would have to be opened up.

One good thing about having a bench microscope is being able to see really close up. I could see how the slider socket was constructed and held together. Using jewellers screwdrivers I was able to pop the two halves apart by unlocking multiple locating pegs that pass from one side to the other, this facilitated the contact removal.

It was evident one middle pair were indeed badly bent, the question now is can they be repaired? If the little lugs don't snap when re-positioned I'll be very lucky but I think they are now always going to be the Achilles-heel of this switch. Still I have no choice but to continue and at least give it a try.

A delicate operation indeed, but bending the contacts very slowly to their correct position will help avoid breakage.

Are all contacts used in the switch? If not, is it possible to use any unused contacts in the damaged positions.

I'm not sure Jon, I'd have to consult and study the circuit.

I have spent the early part of the afternoon persuading the bent contacts back into the near correct shape. They are looking more like they should but I don't know how much further I temp fate by trying to tease them any more. The real problem assuming I can get them back into the switch, will be adjusting them at the correct distance apart so as to allow free running of the slider, whilst making contact but at the same time not binding resulting in the bent contacts as before.

Shudder!!!!!

Chris, you've said that you have two dead N1700 machines in your store - is it your intention to restore both of them or keep one in reserve as a donor?

If the latter, is the same switch used in the N1700 and, if so, have you considered leaving the N1500 in abeyance and tackling the other two to establish if either of them is a hopeless case, then take the switch from it to get the N1500 working as well?

Hi Terry, 

Yes two dead N1700's and a spare bare-bones chassis for parts, so in effect three machines, oh I so wish I could say the same of the N1500.

If by chance you are referring to SK201 & SK202 on the N1700 I had already considered this. Sadly they are of a totally different construction, operation and pin-out, as a result a non starter.

Final update:

This N1500 project has now ground to a halt, the body of SK401 has snapped due to age and heat making the plastic brittle. Absolutely no way will this repair, gutted to have got this far only to be scuppered by a simple but critical part. This VCR will now be put to one side in the vain hope that someday I can find a spare scrapper machine or just PCB 45 with a usable SK401. 

If anybody knows of someone with a scrap player, boards or parts please put them in touch, I will pay a very good ransom for the switch or board.

Thought It worth showing how close I came to success. I had successfully opened SK402, extracted the many contacts, straightened the contacts and was in the final reassembly stage. Believe me I was taking my time and being ever so careful. Obviously the case of SK402 could only take so many flexes before finally letting go.

If you're wondering why I did not separate the two halves completely which would have avoided flexing, well the three end solder points must have been re-soldered in the past. Whoever did it held the heat there too long, melted and fused the plastic together, no way was it going to come apart.

I had an idea, take the top layer of contacts off. Slide in the selector bar, place the top layer of contacts on top then offer up the broken half of the switch case. Finally and carefully jiggle and align the contact holes to the posts and snap it together. This took a few attempts and not breathing on it helped as when I did the wafer thin brass contacts puffed out of place. Its now together and slides freely. 

Now the long and careful re-installation of SK402 and all those flying leads. If this works I'll be amazed but I've got nothing else left but to give it a go. 

Talk about persistence pays off (we hope in this case)! An idea that occurred to me was.....find another Philips slide switch of the same length and number of contacts, take that slider out and fit the slider from the 1500 instead. I think you'll find that the fixed contacts will be the same, it's the slider with the printed contacts that governs what contacts are switched. If there is a gap in the row of contacts on the original, don't take the body of the replacement apart to remove the contact, just cut the pin off or bend it out of the way.

I've never had to do this and there may be a reason why it's not practical but I seem to recall in the dim and distant past that such things were possible.

Otherwise it might be necessary to swap the contacts as well.....

Any luck with this Chris ? or are we looking at a show stopper for now ?

I do take my hat off to you for your determinism 🙂 

Hi Baz, 

Not had a chance to get into the workshop yet as I've been prepping the car for its MOT on Tuesday.

I didn't attempt the re-installation of SK402 or soldering back the rats nest of wires last night as it was late and I was tired, two prime conditions ripe for making mistakes even with copious notes and photos. I shall be back at the bench in an hour or so to attempt the re-installation we shall then see if the switch rebuild has worked or not.

No problem mate, you have to do the right thing in real life.

 It is so easy sometimes on this side of the forum.  far too easy to easy sometimes , to forget that people have their own real life stuff to deal with on the other side,  and expect on demand answers, I do appreciate the hard work you put in, take your time and update us as and when convenient.

Posted by: Red_to_Black

Any luck with this Chris ? or are we looking at a show stopper for now ?

Hi Baz, in answer to your earlier query, its a show stopper I'm afraid. The attempted switch repair would seem to have not yielded the results I had hoped for. I've checked and double checked all the wiring and it is correct.

The VCR is now unusable until a replacement SK402 is obtained and to be honest it could also do with an SK401 as it too is on its last legs, the paxolin slider us bent and not looking at all good for much longer. Until an Sk402 can be sourced and the chances of that are very slim, the story this time really does end here. Still I hope the thread was mildly entertaining even if it did not have a happy or successful outcome. 

Next week I'll think about tackling one of the N1700's, perhaps I'll have more luck with one of those. Possibly I may also start the Thorn 9800 or the 20" Bush A823A

Is it posible to work out what connections need to be made (for playback / EE modes)  and at what time this happens durring the operation of the switch? If a replacement switch can't be found then I'm sure the switching could be done using something else instead of the original switch. OK it won't be truely original but it will still be fuctional.

At the moment I'm thinking of small relays to replace the switch contacts and a simple switch that is operated by the play button to control the relays. If any timing differences are required then some kind of delay to be implimented on those relays.

Not sure Jon, that's all a bit beyond my ability to design and modify accordingly.

Update:

For those who have been following and interested in what went on, here is the detail broken down.

Although the switch is wired in correctly as before, it now presents a whole new bag of faults that were not present before. I will try and explain but it might be easier to do a youtube video to show.

Initial fault upon obtaining the VCR:   Sync playback problems

Prior to any works all the rubber belts need changing.

Electrical Faults

1. The initial and main VCR sync fault was ascertained to be TS462 , the pulse shaper. It had been replaced in the past with an incorrect transistor. The transistor fitted was a CV7004 an OC45 germanium equivalent. Not only was it the wrong type the person had installed it incorrectly with regards to emitter and collector.
2. TS462 was replaced with the correct type a BC158. Now everything was working fine, record, playback E-E etc.
3. Except for one random occurrence of SK401 not aligning with its grab bar. This was addressed and once again the player was working fine

SK402 Fails: 

1. Out of the blue the VCR would no longer power up. 
2. This was traced to SK402.
3. Removing the switch slider from SK402 allowed the VCR to once again power up thus confirming SK402 had some sort of internal short.
4. Obviously without the SK402 slider in situ the playback was never going to function so it needed replacement or if possible repair.
5. Investigating the cause of SK402 confirmed  internal bent contacts
6. SK402 was removed from panel 45, all associated wiring de-soldered. This was procedure was filmed in close detail, photos were take and a manual pad map created for each wire.
7. SK402 was opened up, all contacts were cleaned, all bent contacts were realigned
8. SK402 was reassembled, reinstalled and all point-to-point wiring reestablished.
9. Wiring checked and double checked, it was exactly as before. 

Power up after SK402 Repair# A new set of faults

1. Power applied, now the VCR once again powers up, however not without presenting other fault conditions not present before SK402 fail & repair.

What I have now

• With the VCR powered off, the test card signal fed into the VCR aerial socket and looped out to the TV, the TV is powered on. Selecting CH1 on the TV I'm presented with a crisp and clear test card
• Powering the VCR on, the picture on the TV on CH1 degrades in quality. Powering the VCR off returns the picture to its previous crisp clear state
• Powering the VCR on and selecting CH8 on the TV, the channel used for VCR E-E there is no test card just a blank screen whereas before I would have seen the test card and could tune/detune using the selected VCR channels slider.
• Pressing play on the VCR results in a brief flash on the bottom of the screen but no visual playback.

My assumption at this point being SK402 did not repair and maybe the contacts were not fixed and as such not selecting the correct circuits after all it sis the record/playback switch. I'm certain all the wiring is correct and to be sure I've it checked multiple times, each time it concurs with all the prior photos and pad map.

I've just the minute opened up the panel and discovered SK401 has completely broken. I'm not sure if this would have any bearing on all the above "new" bag of faults and to be frank I cannot see the wood for the forest of trees ..... Ooo it hurts.  ?   

Me again!

I've fixed SK401, however I still have the scenario as detailed above but I've noticed something which is likely a clue to what is going on, even if I've not yet sussed the cause.

Normally and up until now, when I powered the VCR "ON"and with it receiving a signal, the  indicator light "La2" has always been illuminated, however now its does not light. La2 is shown in the photo below. 

La2 illuminates when the VCR tuner receives a colour program and as I say it clearly did before. Now this would confirm the fault I described above and what I'm seeing i.e. no E-E on the TV's AV channel and what the VCR is trying to convey to me.

Problem I have, is it something related to SK401 or something related to SK402 and the contacts repair. No lamp "La2" illumination must be a good clue, hmmm more pondering and circuit study required, perhaps I'm not quite ready to give up! Though I really wish I had all of the manual in English, I have some but certain pages are missing.