1974 Philips N1500: Finally!
An offline chat with Rich (sideband) has raised a point which might be relevant.
"Looking at your dismembered switch when you had straightened out the contacts I noticed that some of the contacts were the reverse of others…. This means that the contacts have to be assembled in the right order. Silly question but are you sure that all the contacts are in the right place?"
I had started to wonder about the contacts, when opening SK402 it was a real struggle and all but the first 3 fell out. My assumption was to mount all contacts whose orientation was not known as shown in the photo below. To be honest I think that's where I have gone wrong.
Note 1: The numbering of SK402 contacts in the photo 1-18, were for my notes and convenience. On the cct diagram they are 51-70. I have placed the real contact numbering in brackets on the photo.
Note 2: Ignore the black loop wire between 11 & 15, I rectified that mistake before reassembly as it was meant to be from pin 11 -17.
What do we know about SK402?
There are nine pairs in total
I know for certain contact pairs 1/2 & 3/4 are correct due to the first three being fixed and I matched the fourth to the other half of the third.
I'm equally confident pairs 11/12 & 17/18 are also now correct.
That leaves just five pairs
Of those five pairs four are of the up variety and one down.
A bit like the old Mastermind game, I have three correct and two incorrect.
Here are the known's. There are four pairs of "UP" and just one single set of "down". This means I have just two pair's incorrectly aligned, as to which position should have the down, I do not know.
- 5/6 (55/56)
- 7/8 (57/58)
- 9/10 (59/60)
- 13/14 (65/66)
- 15/16 (67/68)
The fault condition is the clue to solving this puzzle and one which I've thus far failed to solve. The clue being "no la2 illumination and thus no signal". If I could suss which pair of those five pairs is related or handles that, then it should be a simple case of swapping it over with the other pair and that should fix it. So close yet so far!
Below is how the entire switch is currently set in SK402.
- 1/2 (51/52): contact down (known to be correct)
- 3/4 (53/54): contact up (known to be correct)
- 5/6 (55/56): contact down
- 7/8 (57/58): contact up
- 9/10 (59/60): contact up
- 11/12 (61/62): contact down (100% certain this to be correct)
- 13/14 (65/66): contact up
- 15/16 (67/68): contact up
- 17/18 (69/70): contact down (100% certain this to be correct)
I’m stuffed at present because I cannot figure out which pair from SK402 51-70 on the circuit diagram B , that could be the cause "no la2 illumination/no signal". As a result I think the only way out of this pickle is help identifying the pair or a new SK402 as the contacts will be intact and of the correct orientation.
Would it be possible to ditch the switch totally, and operate a bunch of small relays with a microswitch operated by the lever? No mean feat in itself, but I've been tempted with this solution in the past to replace a duff system switch.
I suggested this last night. I think it is definitely worth looking at. I don't think it would be that difficult to implement, but will need a bit of time to work out the wiring etc. Looks like SK401 would need 8 single pole contacts for play mode and 10 single pole contacts for record mode. SK402 would need 4 single pole contacts for stop mode and 7 single pole contacts for forward mode. The relay count could be reduced by careful choosing of relay contact configurations instead of using single pole relays.
Guys I don't think I need to do that, I'm not that far from solving the problem.
It is my belief that there is just one pair of contacts in SK402 (contacts 51-70) that are incorrectly aligned, though I except I could be wrong. If you read my long post (sorry for it being so verbose) at the top of this page, it explains my thoughts in detail and with evidence to support it.
If anyone can help me track down from the cct B, which pair of the identified five is associated with the "no signal la2 illumination", I reckon I will have this fault solved.
I've now located all the contacts for SK402 on circuit diagram B. Contact pairs 51/52, 53/54, 61/62 & 69/70 are I believe, 100% correctly aligned.
To view maximum size image click on image to launch viewer. Then right click image and choose open image in new tab. You will now have max size.
As per my notes (see first post on this page) suspicion falls upon 55/56, 57/58, 59/60, 65/66, 67/68. Three pairs are correctly aligned, two pairs are incorrectly aligned to cause the no signal condition. Just need to figure which and this is where I really need help.
Edit: Perhaps someone with a N1500 could look down their own SK402 and report here the contact order with regards to up down alignment of 55 thru 70 as to be honest i'm at a loss and not even sure of anything now.
SK401 & Sk402 need replacing as to be frank they were in a sorry state to start with. This repair pause now until I can find another scrap player as I need spares especially as I want to actively use this machine in my display room.
Hi All, Just had a look at your N1500 rebuild Chris. When you get the replacement switches DO NOT PULL THE SLIDER OUT! If you do and re-insert the slider then most likely the spring contacts will get bent on re-inserting. A small amount of contact cleaner if needed but doubt you will need to use any. On fixing the servos which rarely fail, disconnect the eddy current break coil first and see if the sampling pulse on the ramp now goes the other way. If it is still too slow then you will be looking for a mechanical problem. Worked on these a few times in the late 70's Cleaning Philips belt goo I use Cif, gets the stuff off your fingers too.
Hi All, Just had a look at your N1500 rebuild Chris. When you get the replacement switches DO NOT PULL THE SLIDER OUT! If you do and re-insert the slider then most likely the spring contacts will get bent on re-inserting.
Actually you should be able to pull the slider out and re-insert without any damage....that is assuming of course that the slider itself isn't damaged. When I worked for Philips, we did this all the time and I doubt that there were many that didn't reassemble OK. The leading edge of the slider is chamfered and pushes the contacts open as it is re-inserted.