Help [Closed] Philips N1500 - An Adventure in Patience?
Newbie here, who has been pointed to this forum by a YouTube contributor to one of my uploads, suggesting this is the best place for help.
After finally having enough time since acquiring a cosmetically fine Philips N1500 over 5 years ago, a few weeks ago, it was removed from cupboard storage. With the loading mechanism repaired, new belts and pinch roller fitted, idler wheel looking in good condition, and PCB’s visually checked for obvious component problems, the result [clip from a 1976 edition of The Sky At Night] is as per the link below:
The eddy current brake for the tape transport has already been suggested as a possible cause, but, silly me decided to check diodes and resistors on panel 23 for servo playback first, have damaged at least one diode in the process, and am awaiting a replacement.
Service Manual is available, but as yet, no oscilloscope or capacitor meter (are both essential?), and am able to read circuit diagrams fairly easily, but, having read and thoroughly enjoyed in particular member crustytv’s posts and blog regarding his repair efforts with three of these machines, I would really appreciate any help with this one, in particular where to start the fault finding.
My interest in this machine is purely to archive old videotapes (currently have about two dozen with confirmed VCR format recordings, including at least three BBC studio masters of Rentaghost!) and share finds on the same YouTube channel as the above link. Have had great success with VCR-LP transfers in the past, although most of my work is with a Sanyo Betacord VTC5150.
Being honest, there is nothing or very little I can provide to others in respect of vintage electronics, and hopefully this will not be held against me.
All suggestions for help, together with any offers to repair the machine, will be gladly taken on board, and updates on any repair progress will of course be posted.
@betaphil You will need an Oscilloscope for most VTR fault finding and in particular respect to fault finding this type of problem. Your capstan is not locked here. You will need to look at the sampling pulse on the capstan ramp first to see if it is continually traveling up or down the ramp or if the sampling pulse is missing. If the sampling pulse is missing then you will have to go back to the CTL head amp and circuitry, unlikely. If is is running to slow, disconnect the capstan eddy current brake at the coil. The eddy current brakes don't fail. If the capstan still runs slow then your problem is mechanical. Make sure the Drum and Capstan motor bearings are lubricated with a drop of thin oil. Hope your tapes are in good order and haven't gone sticky.
My interest in this machine is purely to archive old videotapes (currently have about two dozen with confirmed VCR format recordings, including at least three BBC studio masters of Rentaghost!)
Might I ask what makes you think that something recorded on a domestic-quality machine is a "master"?
@hurty Thanks for your suggestions, and I will try the method with disconnecting the eddy brake first. As for the tapes themselves, I always unwind/rewind every one (manually, using an old cine reel contraption) and clean the internal surfaces of both the supply and take-up reels. Time consuming, but worth the effort if it prolongs head life.
@cathovisor Please excuse me if I have used the wrong terminology, and/or made the wrong assumption. Photos of one of the tapes referenced and it’s corresponding case have been included, this tape in particular having already been tried in the N1500 (first few minutes only), and prior to the programme itself starting there is a test card, followed by a slate with production details and mechanical countdown clock.
I'm looking to see if 1/5/80 tallies with any transmission dates on BBC Genome, but it doesn't.
It does look like it might be a final cut made for someone's benefit though - but a "master" it most definitely is not. That'd be on 2" or 1" videotape.
@cathovisor Oh well, I stand corrected. That’s something else I have “definitely” got wrong as an amateur archivist of 15 years. Hopefully future replies on this post will concentrate on restoration assistance for the N1500.
All the best.
Well, I've been in broadcasting for 37 years now: I even worked on the later series of Rentaghost in 1984/5.
Hopefully you'll get the assistance you need to sort the machine out, either from here or UKVRRR where I note you have a similar thread.
@hurty The capstan eddy current brake was disconnected as you suggested, and the tape ran slightly faster, but, although the frequency of the picture sync lock reduced in frequency, the audio was even better than before with no intermittent wow. A mixture of mechanical and electronic issues?
Still awaiting the arrival of an oscilloscope.
To anyone still following this old thread, have continued working away on this N1500. The drive motors for the capstan and head drum were removed, cleaned, bearings greased, reassembled, slight buckle in capstan brake disc sorted, pinch roller and idler tyre treated with Platenclene, and all running freely.
Power applied, and now the tape drive runs even with a cassette inserted in STOP mode (that did not happen before), and dare not press START in this instance for fear of tape damage. Friction items checked and appear correctly adjusted, so could it be capstan eddy brake not working, one of the switches not working correctly during threading or at end of cycle, or something electronic? Oscilloscope now available, but where to begin?
Seems so close to working, but have lost patience right now.
All ideas and suggestions welcome...
In the absence of knowing for certain where to start fault-finding, and assuming there are servo problems, have now begun to work through the checks on the servo PCB [panel 23 in the machine] as listed in the Service Manual.
With reference to the attachments, a more saw tooth than square wave was scoped at point 225, although from the section of the circuit diagram, that would appear to be the correct shape, however, it was not possible to obtain a 20ms pulse with any adjustment of R293.
As for using an external trigger, unsure if I managed that procedure correctly: edge, pulse, or video trigger, and should two waveforms have been shown on the scope instead of just the one? The outcome was that R293 could not be further adjusted to give a completely stationary wave.
Any thoughts and advice welcome. More updates as I work through the remaining sections and the remaining seven variable resistors on this board.
No longer have the capacity to learn and/or understand correct oscilloscope usage, and the trigger function is completely beyond me so unable to check the servos correctly.
Machine and tapes will now be skipped.