It is currently Mon Dec 11, 2017 5:02 am

Fun with a Philips N1500, or Recording Ramblings....

 
Posts: 231
Joined: Wed Jan 23, 2013 11:40 pm
Location: Swansea, South Wales

Fun with a Philips N1500, or Recording Ramblings....

Post by Alastair » Thu Jan 01, 2015 4:41 pm

Recently, Ive dug out my old N1500 machine that I last looked at about 2 years ago. At that time, it was plagued by the Lockfit Transistors popping off, first in the regulated PSU, 12V rail, then in the Head-Servo, after that, the Capstan-Servo, Then FM Video gain stages and finally playback sound.
All in all, I changed 11 of 'em in the space of about 4 or 5 hours actual playing time, over the course of a week messing round.
It then developed a very poor E-E picture and poor recording, so I guessed another somewhere had failed and put the machine aside.

I decided to replace All--Or as many as is practical--of the horrible Lockfits in the machine. Thankfully, there's not a huge variety of types used, mainly BC147, BC148, BC149, BF194, and BC195/6
I bought 40 of each of the closest newer or equivalents (BC147, 148, 149, BF194 = BC107, 108, 109 and BF494/6/8 used) and set to work.....

The job was mostly completed in 3/4 evenings of messing round and in the end just a couple were left. I counted the ones removed, and Ive got 112 Lockfits in a small ceramic dish.....

This restored playback and E-E, but I also wanted to be able to run straight Video into and out of the machine. Play out is already catered for on a DIN socket which gives out what is in effect, 'S-Video' signal, a separate Chroma and Luma signals. I found that these can be combined to make for a fully usable compo video signal, or left separate and used via an S-Video input on a monitor/TV set.

For Inputting compo-video a little more work was required.
Looking at the schematics of the Tuner/IF block suggested that the Luma and Chroma are detected separately, and fed their separate routes finally being combined at the recording amplifier before the video-heads.

As an experiment, I cut the track at a point just after U508 pin 1, U508 being the Luminance detector, and prior to the luma delay-line driver, TS4050 and via a 10uF cap, I input CVBS/full composite video signal from a set-top-box.
A test-recording was made, which surprisingly worked pretty well, all be it Monochrome, and a little low-contrast level. A small adjustment to the rec-luma level sorted that, making it approximately the same level as a previous recording.

A similar approach was tried for the Chroma. The Chroma Detector U516 outputs a Chroma signal ( the test-waveform shows a full composite signal at this point on the schematic) on pin 1 The track from this pin was cut and via a 0.22uF cap was also connected to the composite video source from the set-top-box.

Another test-recording gave very acceptable results! While this modification was only an experiment, it proves concept so at some stage, I'll make it switchable between Added Input, and the built-in Analoge tuner. As the luma/chroma is being input After any AGC at least that infernal Macrovision shouldnt upset it (I hope!)

The Video-heads in this machine, while working are pretty worn, its Very sensitive to the tape used, any slight damage/crease etc will cause picture disturbance or with one tape-no usable function at all, while a good tape gives nice results.

Various attempts have been made to help the problem, such as tape path cleaning and alignment, back-tension clutch cleaning etc,--all sorts of messing round, but it came to the point that I have to accept the fact the heads just are Not up to it anymore--No surprise really, They are of the very earliest type, not having the connecting wires coming up through the top in those little black round things, all wiring is done underneath the disc.
A few months ago, I won a new/NOS boxed head-drum assy for an N1700 from the usual spares-auction-site, Fleagay for a pretty cheap price. It was decided to carry out the period modification to this machine and fit the new 1700 heads.

This modification involves machining down the Capstan Motor pulley to half its original size and also to machine the capstan shaft itself. The original article was in the Television Magazine around 1982 ish also called for the addition of another pick-up head for the capstan servo.
--Experience over the years has shown this addition isn't completely necessary, capstan servo still locks solidly with just the original one.

Many years ago, I did this to a machine and still had the various parts I had used. At that time, try as I did, I couldn't machine the actual Capstan shaft, it was just Too hard. I made a complete new shaft, but again had problems due to the fact, my machining wasn't good enough to make an accurate cut at the point the tape is gripped by the pinch-roller. --All I ended up with was screwed up tapes, so I gave up on that, and settled for just halving the tape-speed.
I fitted the machined Pulley and brake-disc to the capstan motor, and carefully fitted the new head-drum, after adding just a little extra epoxy to the head-chips, (the original epoxy seems to have a reputation for failing leading to a head chip being flung off into orbit) and made a test recording.

The results were very impressive, producing a very clean although a little soft-focus picture due to the 3MHz limited video bandwidth. Colour was excellent and there was very little if any edge-noise often seen with old video recordings. All in all, pretty happy the machine is usable although isn't any official video format as its tape-speed is still too high at 7 odd cm/S instead of the N1700 6 odd cm/S, but at least a whole movie can now be recorded onto one single cassette.

A little bit more work to be done, like sorting an audio input, curing the hum on the sound channel and making things a little more permanent adding a Tuner/AUX input switch etc....

I would like to than Baz, (Red to Black) for his help in supplying some service-info, as all the info I had up to recently is in Dutch. His manual was excellent in locating various little issues I had with the tape lacing and helping find a dry-joint causing no colour on record. :thumb

 
Posts: 2986
Joined: Thu Jun 28, 2012 12:20 pm
Location: The Vale Of York

Re: Fun with a Philips N1500, or Recording Ramblings....

Post by Katie Bush » Thu Jan 01, 2015 9:52 pm

Hi Alistair,

Is your machine an original N1500 (all brushed aluminium and wood effect) or the later N1502 (two tone plastic appearance)?

I'm just curious because I can remember the "Long Play VCR" article in television, but was given to believe it was only suitable for the N1502 and its DC motors.. The original N1500 having AC motors were synchronous (as I recall) and couldn't be modified to run at a lower RPM.. Or is that where your capstan issue comes into the equation?

I can't remember if the correctly modified N1502 was wholly compatible with the N1700, but can see no reason why it shouldn't be.

Marion

 
Posts: 1218
Joined: Thu Jul 28, 2011 10:28 pm
Location: Sunderland

Re: Fun with a Philips N1500, or Recording Ramblings....

Post by Red_to_Black » Thu Jan 01, 2015 10:59 pm

Katie Bush wrote:


I can't remember if the correctly modified N1502 was wholly compatible with the N1700, but can see no reason why it shouldn't be.

Marion


Hi Marion, as far as I recall the modified 1502 machine as per the TV mag wasn't compatible with the later 1700 series, this was due to the heads on the latter having azimuth offset heads to eliminate cross-talk between the heads where as the original 1500 machine used guard bands or a gap between subsequent tracks to achieve the same thing with non-offset heads.

Hence the longer playing time of the 1700 machines by using up the space the guard bands previously used on the earlier series to record video tracks in on the latter, this allowed a more compact track layout and denser recording medium by laying each subsequent video track side by side.

That is a machine of either type (1500 or 1700 series) would not be able to read the video tracks of the other, now Al has created yet another variant :bba

 
Posts: 2986
Joined: Thu Jun 28, 2012 12:20 pm
Location: The Vale Of York

Re: Fun with a Philips N1500, or Recording Ramblings....

Post by Katie Bush » Thu Jan 01, 2015 11:13 pm

Hi R2B,

As I recall it, the article specified replacing the N1502 head disc with one for the N1700.. As I understood it, the modification slowed down the tape transport speed to half its original inch/second and eliminated the guard bands.. In so doing, it necessitated the slant azimuth heads to be fitted.

This is why I can see no reason why the modified machine would be incompatible with a native N1700, unless there were any issues surrounding the relative position/timing of the sync head and video heads, which would seem unlikely to me.

Marion

 
Posts: 231
Joined: Wed Jan 23, 2013 11:40 pm
Location: Swansea, South Wales

Re: Fun with a Philips N1500, or Recording Ramblings....

Post by Alastair » Thu Jan 01, 2015 11:24 pm

Hi Marion,

The machine is the early N1500, brushed ally, fake wood covered chipboard, and yes--It has Two Synchronous motors This machine is a very early one--without the cat-gut safety strings that prevent the springs being shoved into the mains voltage-selector when the lacing string breaks. Oh--What fun! :aac

The mod involved machining the Cap-motor Pulley down from 1" diameter to 1/2 inch, and re-cutting the belt groove thus halving the capstan speed. The servos remained unchanged, and the belt still has enough tension to use the original, even on the reduced pulley size.

The N1501 was a Very similar machine, basically a slightly updated N1500,-- it had black anodised brushed ally--much the same as the N1500--but black, and a rather boring grey covered, moulded beige plastic case/frame replacing the wood-chip, and with the Co. logo on the front right-hand side under the cooker-timer clock.

It had improvements to chroma circuits and a still picture feature on 'stop' function, switchable with one of the buttons by the On/Off switches--It retained the usual string and spring lacing and two AC synchronous motors and eddy-current servo disc-brakes of the earlier machine.

The N1502 was more like the N1700 series with DC motors and associated servos, a more robust lacing arrangement very similar to the 1700 series, but still the max 1 hour play time.

Not sure about mods to the 1502, (I don't think there were any mods for it, I know I had one and never bothered much with it) but I know that it was possible to make an N1700/1/2 play at yet again half-speed by changing a resistor in the Cap-servo can, making it similar to the Grundig SVR standard 4 hours play/record, although there was some picture degradation.

 
Posts: 1218
Joined: Thu Jul 28, 2011 10:28 pm
Location: Sunderland

Re: Fun with a Philips N1500, or Recording Ramblings....

Post by Red_to_Black » Thu Jan 01, 2015 11:29 pm

Hi Marion

As far as I can recall in the mag there was different "degrees" or levels of modification :bba some just relatively simple and easily reversible giving a sort of "long play 1500" format.

I suppose going the whole hog and replacing the upper drum with the 1700 type as well would result in compatibility between the fully modified machine and the later series. :aab , although I am not sure if there was other subtle differences between the two series/formats

My memory is not as good these days to say one way or the other :qq1 , If I recall, one article in the TV mag used a switch on the front to enable a sort of long play version of the 1500 to be selected or not.

I might have a copy of that article to check, I will have to have a look though.

Happy New year to you all the same. :cca

 
Posts: 231
Joined: Wed Jan 23, 2013 11:40 pm
Location: Swansea, South Wales

Re: Fun with a Philips N1500, or Recording Ramblings....

Post by Alastair » Thu Jan 01, 2015 11:35 pm

Baz--

The main reason that the 1500/1 wouldn't be fully compatable wasnt because of the Video-Head drum--as part of the extended-play mod you replace the 1500 130uM track guard-band video-heads with the 1700 85uM track slant-azimuth non-guard-band video-heads.

You would need also to change the ACE head, as the control-track is in slightly different place on the 1500/1/2 machines, but otherwise, should be fully compatable with a 1700 recording providing both the Cap-Motor and Cap-Shaft are machined appropriately....

Apparently, the different placement of the control-track left room for an unused future track--maybe used on the 1420 or is it the 1520 four-head editing machine.....
Control-track of N1500 is approx 1.5mm from the top of the tape edge and only about 0.75mm high. The N1700 control-track is about 1.2mm and level with the top of tape edge.

--Ive only gone half-a-hog by only replacing the Heads to N1700 type and machining the Motor-pulley, so mine isn't compatable with anything! :aaj
Last edited by Alastair on Thu Jan 01, 2015 11:46 pm, edited 1 time in total.

 
Posts: 1218
Joined: Thu Jul 28, 2011 10:28 pm
Location: Sunderland

Re: Fun with a Philips N1500, or Recording Ramblings....

Post by Red_to_Black » Thu Jan 01, 2015 11:45 pm

Good write up Al :thumb

I thought there were other subtle differences between the two formats :bba , as you have now confirmed.

I thought the TV mag article was just a quick'n'dirty approach to extending the recording time of the 1501/1502 machines, there may have been more than one article, I cannot remember now. :bbd

I had very little to do with these machines, they were mostly gone by the time I entered the trade, I probably saw more V2000 machines and even these were few and far between (thank god!), I was one of the very few TV repair people that still entertained Beta machines in my neck of the woods at that time.

I never actually carried out any of the mods in the mag, but do recall reading them out of interest at the time though.

 
Posts: 231
Joined: Wed Jan 23, 2013 11:40 pm
Location: Swansea, South Wales

Re: Fun with a Philips N1500, or Recording Ramblings....

Post by Alastair » Thu Jan 01, 2015 11:52 pm

As I remember, there were a series of articles, some for the 1500 series and others for the N1700 series. I think I got a bit confused too until I thought about it, but clearly remember two different articles for the different series machines. M Phelan I think was one author....

The N1700 was modded electronically, so switches were used for SP/LP on those, but once modded its not easy to go backwards on an N1500/01--without just putting the original parts back to standard. The slant-azimuth heads wont pick up the straight heads tracks to any usable extent--I tried! :qq1

 
Posts: 1218
Joined: Thu Jul 28, 2011 10:28 pm
Location: Sunderland

Re: Fun with a Philips N1500, or Recording Ramblings....

Post by Red_to_Black » Fri Jan 02, 2015 12:26 am

Al both you and Marion are most probably correct, my memory is getting steadily worse I swear :ccb , it must be an age thing with me :aa , that and my career change a few years ago where I have so much other stuff to remember, my hard drive must be full :bba .

Now that you mention it there must have been several different articles, the Mike Phelan one certainly rings a bell, I may or may not have read all of them let alone remember them properly!

All that said, one of the articles I read I was fairly sure was a quick and easy mod (or bodge) to extend the recording time of a 1500 format machine, without making it compatible to the 1700 series, but as you say it could have been to add LP to the 1700 series, I am about now doubting my sanity completely! :aak


Return to Video Tape Recorders



Who is online

Users browsing this forum: No registered users and 1 guest