Philips N4308/85 Basic Electrical Fault Finding

[BrianAllen]

Good evening gents,

I have just purchased another 4308; will need cleaning up and the usual replacement belts and clutch rubbers but nowhere near as bad as my previous 4308 purchase.

This machine will not power up and I am seeking advice on some basic checks that I need to carry out. If you know of any previous posts on the forum or maybe a youtube tutorial that may point me in the right direction I would be very grateful.

Thank you.

[dazzlevision]

I am assuming that “does not power up” means the motor and the amplifier are “dead”...?

Does this /85 version of the N4308 have both a mains transformer and a motor? Later versions of the very similar N4307 didn’t have a mains transformer fitted but instead used the motor windings as the mains transformer.

If there is a mains transformer, it should have a thermal fuse nestled in the windings, which may have gone open circuit if there is excessive current bring drawn from the transformer (or if the transformer has short circuit turns). If the thermal fuse has operated, the primary of the transformer will be effectively isolated from the mains supply.

Alternatively, if the on-off switch is faulty (one or both poles open circuit), the mains will not reach the transformer.

[BrianAllen]

Hello, nothing operational; not even the lamp in the VU meter.

Yes, this model has the transformer. As usual some great advice from the forum, so will start with checking the on-off switch and then the transformer.

Thank you.

[hillmanie]

As the least knowledgeable of your subscribers I'll just state what I do in this very same situation. (I have > one 4308) though hesitate posting such simple stuff in the presence of the awesome knowledge of so many real technicians here on whom I rely
I check the mains input wiring and the switch with a simple meter to see if I get an OHMS reading starting with the plugtop fuse, thorough the switch and on to the transformer via any component/fuse in between. I then meter the primary winding of the trans If there's no break in continuity to that point I power up and check for voltage on the secondary winding of the mains trans. If not the tans or solder contacts suspect. If there is sec voltage I'm in a whole new world of blunderland. But to recap a little my very first test after checking plugtop/fuse connections I switch on the unpowered recorder and meter the two pins of the plug. If the path to the trans is clear then I'll get a low ohms reading which is the resistance of the primary winding.
With these tests I've found amongst other faults an open circuit switch and and a broken wire at the transformer, both manageable fixes
TT

[dazzlevision]

Here is an extract of the circuit diagram, showing the mains input and up to the mains transformer's secondary. Z1 is the thermal fuse fitted in the mains transformer.

You could redraw the diagram to show the wiring with the mains voltage selector just set to 240, to make it easier to follow.

[DMcMahon]

If I am interpreting that schematic correctly, it looks like the capstan motor will run as soon as the mains switch is switched on from voltage derived from transformer primary, so if motor not running then problem is with the switch or mains wiring or transformer (this assumes that the motor is good).

I see there is also a lamp indicator off a secondary tap of the mains transformer.

[AC/HL]

Originally Posted by hillmanie

...though hesitate posting such simple stuff in the presence of the awesome knowledge of so many real technicians here on whom I rely

Quite the opposite. With experience it's easy to forget how every one of us started out. Some basics become second nature, and are completed almost unthinking. Illustrating the other side of the coin can be useful to other beginners.

[BrianAllen]

Thank you for your assistance.

As I wrote in an earlier post, I will not be offended if you refer me to basic simple testing etc, so no need to hold back as I am here to learn.

I did test the on-off switch and it is operating ok but on closer inspection, I noticed that a wire on the transformer has broken away.

I have attached a photo as (correct me if I am wrong) but I am thinking it may be best to release the cable ties and check all of the connections.

[DMcMahon]

Well found ! yes that could be sensible, however be very careful, transformer wires can be very delicate, you do not want any more to break off. Stating the obvious but always ensure when working inside the unit that the mains cable is unplugged from the wall socket, i.e not just switched off at the wall.

For any live testing inside the unit, be extra vigilant and only do it if really necessary and you are confident you know what you are doing in terms of your own personal safety.

A mains voltage electric shock is unpleasant at best and at worst could be lethal.

[hillmanie]

Re safety rubber gloves are advised plus a rubber mat underfoot I prefer
TT

[julie_m]

For the second time today, the return path in an AC electric shock is not through the soles of your feet; but through the whole of the surface of your body, which is one plate of a capacitor, with the Earth as the other plate. Increasing the thickness of the dielectric over a small part of the overlapping area really will not make much difference.

[BrianAllen]

Good news.

I have now located another wire which was broken; it was one of those very fine wires of which may be difficult to repair. I managed to put a link into the brown wire but the very fine wire is only temporarily just about touching/resting on the broken wire.

Anyway, I powered up and motor now running and VU lit up.

Further to a previous post regarding tools/equipment that you can't be without, my first purchases will have to be a decent work lamp and a magnifying glass (as recommended by members).

Once again, thank you for your advice, it really is appreciated.

[hillmanie]

Originally Posted by julie_m

For the second time today, the return path in an AC electric shock is not through the soles of your feet; but through the whole of the surface of your body, which is one plate of a capacitor, with the Earth as the other plate. Increasing the thickness of the dielectric over a small part of the overlapping area really will not make much difference.

Sorry all for my misleading 'advice'. Thanks for instructing me julie m but didn't see your first time input on this thread and I've searched this list of postings without success. I guess there was another non-shock reason eg operator comfort why so many workshops of my acquaintance insisted on those two work practices when working on elec apparatus.
Regards
TT

[DMcMahon]

Julie was referencing a separate post that she had responded to, on a similar subject.

[hillmanie]

Thanks DMcMahon. I hadn't seen that conference. As an r-r freak that's the only one I subscribe to
Regards
TT

[DMcMahon]

I also only normally look at R2R but when I saw her message to you, I went looking out of interest, by clicking on someones Username, under the listed options is "Find More Posts", i.e. you can see the various posts by that person in date/time order..

[hillmanie]

Thanks a lot. Am continually learning more about this great conference and the sympathetic encouragement from our moderators for newbies.
TT

[hillmanie]

Originally Posted by BrianAllen

Further to a previous post regarding tools/equipment that you can't be without, my first purchases will have to be a decent work lamp and a magnifying glass (as recommended by members).

Don't know if they are still available but I recall a thing called Anglepoise a jointed set up. There may well be a modern improved version of these lamps.I have an endoscope which is best in good light with the advantage of picturing and saving the work object
TT

[BrianAllen]

Good thinking, an anglepoise will be ideal.

[AC/HL]

https://www.vintage-radio.net/forum/....php?p=1206836