The Philips VCR system was groundbreaking and brought together many advances in video recording technology to produce the first truly practical home video cassette system.
The VCR format was introduced in 1972, just after the Sony U-matic format in 1971. Although at first glance the two might appear to have been competing formats, they were aimed at very different markets. After failing as a consumer format, U-matic was marketed as a professional television production format, whilst VCR was targeted particularly at educational but also domestic users.
The very first Philips N1500 model included all the essential elements of a domestic video cassette recorder:
- Simple loading of cassette and simple operation by “Piano Key” controls, with full auto-stop at tape ends.
- A tuner for recording off-air television programmes.
- A clock with timer for unattended recordings.
- A modulator to allow connection to a normal (for the time) television receiver without audio and video input connectors.
First thing I’m going to need to do is study the service manual ( those interested and with access will find the manual in the data library) to familiarise myself with how the various circuits and mechanics expect to operate.
One area I’m fearful of is the “string” loading, I’ve no doubt that will give me a few stressful evenings if it requires work and you can bet my luck means it will.
At the time of release with VAT at 25% the machine retailed at just a little over £500, this was an astronomical sum of money for the consumer to part. A very complex machine cramming in over 136 transistors, 67 diodes and 4 i.c.’s
Hope this new addition ends up producing an equally good picture as shown in a photo from the brochure below. I will update the blog when it arrives.
Work commences on cleaning up the belts that have turned to goo.
Its actually very evil stuff and unless cleaned off thoroughly before fitting new, will clearly prevent the mechanism from functioning as intended. The trick is also to not get it on your hands.
In this VCR the belts have all completely perished and wherever they landed have then proceeded to revert to tar. Whilst this for the most part is annoyance and they have landed mostly on the PCB and components, inevitably the pulleys and drums have a fair share and these must be totally clean. I can only hope remnants have not found their way into extremely difficult to get at drive bearings/gears or mechanics. Time will tell as I progress with the repair, its certainly a long laborious messy task.
Further Update: Belts fitted and function tests
Work on cleaning the liquefied drive belts continues, I’m now tackling the worst one.
The video head drum eddy disc was barely able to turn, the cause of this was due to a belt collapsing onto the reverse side of the disc and smearing itself over the surface. As a result of this it also deposited itself all over the gap where the disc passes through where the eddy current is developed/monitored, thus causing a goo trap and super efficient brake.
These belts are an absolute disgrace and nightmare to clean, despite great efforts to avoid getting covered in muck, invariably your fingers get plastered. I’ve also had to clean the belt brushes as they too ended up covered in belt goo. The belts seems to have got themselves everywhere, I’m wondering if in the players past life they had started to liquefy and someone started it up spinning the belts off in all directions.
Anyway once this major one is cleaned up I have just one smaller disc to clean and then I should be ready to fit the new belts. I will leave getting the remnants from the PCB until later on in the repair. I don’t want to invest too much time on the clean up only to find the device is a no go. I just need to clean the areas of the mechanism that are compromised from mechanically operating due to the goo and see what gives.
The goo clean up is now complete, all belts are in place, drive, take up and the eddy discs appeared to run freely.
Base line evaluation of the power supply, cold checks of critical components including fuses. Assuming nothing untoward is discovered, I’ll bring it up slowly on the variac.
Power supply checked out OK and the device was brought up on the variac over about 20 mins, no dramatics and 240V was attained. Decided to select “on” which should load the main drum assembly and test the dial cord load.
This was not so good. Initially it did fully load and the head stayed spinning, only the once though, It now attempts to load but ceases part way and disengages, the head is not spinning. No idea yet as to what or why this is occurring, for me I’m in uncharted waters. There does seem to be some slack in the loading cord but I’m unsure if this is the cause.
Trouble is the manual is in Dutch so understanding the operational characteristics of the mechanism is going to take some considerable time. Not relishing dis-assembling the loading cord assembly.
It was discovered that there was a setup fault with the main head drum eddy disc. The problem would appear to have been the eddy disc binding on the coil gap. I think this was caused by not one but probably two causes.
The first being the head drum top tension bar which is located in the top-deck, this was bent and not making contact with the spindle point and tension plate. The result being the whole assembly could float up and down, which would explain the different behaviour when in the vertical as opposed to the horizontal position. With the deck in the horizontal position, thus allowing gravity to pull the head drum down, the tension bar was adjusted so as to keep it firmly in place.
Secondly the gap on the coil gate was perfectly fine as can be seen from the photo’s below. However when the eddy disc is aligned within the gap, it still has enough play to move up and down therefore binding is possible and exacerbated if the top-deck tension bar is also not doing its job. The two allen slotted grubs fix the disc position, this time I added two shims either side of the disc before locking them up. Its quite possible all this information is covered in the manual but as I’ve stated in this thread and elsewhere, its all in Dutch. Manually rotating the eddy disc now, it appears to run freely with zero binding powering up and testing the fault is now cleared.
Further progress; tape transport function tests. Does it load the tape, play, rewind, fast forward and stop.
The tapes I have don’t appear to have N1500 recordings on them I suspect they have N1700 content. So without content to playback I decided to use my test card generator and record the card. The generator can output a colour test card and a B&W test card. I chose to record the B&W card whilst it would output a live colour Test card F that way I would know I was recording and playing back. The N1500 did record the signal and playback but it appears to have sync problems (see video below).
I gently tried the finger test on the top of the head drum, adding just a tiny bit of resistance, the effect of this was to consistently stop the picture from attaining any sync whatsoever. When the finger was removed the picture output reverted back to its previous state of coming and going, sometimes staying for an extended period of a good few seconds, before once again returning to its fluctuating sync state.
I guess this suggests the that drum is not attaining/maintaining its speed due to incorrect/sub-optimal eddy braking and as such consistent sync is not achieved?
As far as I can tell the drum is free running and not impeded, I’m left wondering if the circuit that controls the braking, (eddy current) is running in a sub-optimal state and how I now investigate this. This leads me right back to the question I posed a couple of days ago, that surely I should not have to solely rely on a test tape, that I should be able to investigate and rectify the speed problem with a scope and logical fault finding within the servo circuit.
Continuing the checks on panel 23, servo PCB. The voltages in the head (Fluke) and tape (Metrix) servos are looking good. The reference pulse voltage and timings at 12V @20ms (TEK) appear present but with one interesting feature, that being the amplitude of the pulse seems to fluctuate. It peaks at 12V but drops and recovers repeatedly. I would have expected it to be a consistent 20ms 12V pulse. You can see this on the scope capture the fourth pulse collapsed, I will film it later as its easier to see in a live situation.
Next I’ll check the A-stable, Saw-tooth gen, sample gate and storage, if the reference pulse is fluctuating then that is likely to put the rest of this part of the circuit out of whack.
Scoping the saw-tooth wave-form at the anode of D213(BAX13) confirms things are a little strange.
For a start the saw-tooth is a square wave also its amplitude is equally fluctuating from between 6.7V – 14V, it should be no more than 5V. Also the period should be 20ms, I have twice what it should be at 40ms. I think I may have found (or maybe I’m missing something obvious and navigating yet another one of my rabbit holes) the source or one of the sources of my troubles and perhaps the head servo is compromised by these findings.
It might well be a rabbit hole but I will trace back through the circuit to see where the reference pulse is being generated and find the cause of the fluctuation.
It’s spatially taxing working on this N1500 from the circuit diagrams and plan views. You are required to mentally flip and invert the rotation of the boards as shown on paper to what is physically before you. I find my brain keeps resetting and I have to reestablish a frame of reference, very tiring. As mentioned before, not helped at all by no screen print on either side of the boards to assist the engineer, what were Philips thinking!!!!
Anyhow ….. that said after doing mental gymnastics I was still having a devil of a job locating the pulse shaper transistor, its listed and TS462 a BC158 (lockfit). It soon became apparent it must be under the little delay line daughter board as shown in pic 1 below.
Upon removing the delay line module I was greeted with an abhorrent repair and very odd substitution, so had the pulse shaper failed before? Why the god awful exposed leads which can easily short out to the underside of the delay line module. I find it hard to believe a university maintenance lab would condone such work. Perhaps it was some smelly plant inspired, student attempt at a fix that consigned this player to its cupboard slumber.
The transistor fitted instead of the correct BC158 is a PNP CV7004, an OC45 equiv. I can only surmise the previous person to work on the N1500 assumed as it was a PNP it would be OK. Perhaps that’s all they had to hand at the time, found it didn’t work and the player was then consigned to the cupboard until 30+ years later it falls onto my bench.
Could this be the source of my intermittent 12V reference pulse problem? We shall see. It will be interesting to see what happens when its replaced with the correct BC158. I’m hopeful as according to the manual when in record mode the servo reference is the field sync information contained within the video signal. The separated mixed sync pulses are fed to TS461 (the field pulse separator) then clipped by TS462 (the pulse shaper) to produce a clean ( is the CV7004 doing that? Its only 4Mhz as opposed to a BC158 at 100Mhz) positive going field sync pulse. Once TS462 is replaced I would hope to have a clean stable Reference field sync pulse to lock the master reference oscillator TS228 and TS229, I’ll need to check those two are also OK.
If all is looking good with regards to voltages and wave-forms, I will do a test record and playback again. If it does playback OK I guess we only know it works with itself hence needing a test N1500 recording from another source. If it still gives sync problems its back to the drawing board.
Well I’m done for tonight.
Transistor datasheet for the currently fitted CV7004 (OC45 equivalent)
Type Designator: OC45
Material of Transistor: Ge
Maximum Collector Power Dissipation (Pc): 0.083 W
Maximum Collector-Base Voltage |Vcb|: 15 V
Maximum Collector-Emitter Voltage |Vce|: 15 V
Maximum Emitter-Base Voltage |Veb|: 12 V
Maximum Collector Current |Ic max|: 0.01 A
Max. Operating Junction Temperature (Tj): 80 °C
Transition Frequency (ft): 4 MHz
Transistor datasheet for the transistor that should be fitted for the Pulse Shaper
Type Designator: BC158
Material of Transistor: Si
Maximum Collector Power Dissipation (Pc): 0.3 W
Maximum Collector-Base Voltage |Vcb|: 30 V
Maximum Collector-Emitter Voltage |Vce|: 25 V
Maximum Emitter-Base Voltage |Veb|: 5 V
Maximum Collector Current |Ic max|: 0.1 A
Max. Operating Junction Temperature (Tj): 125 °C
Transition Frequency (ft): 100 MHz
The CV7004 has been removed and well, the less said about the prior work the better. Whoever it was not only fitted the wrong type of transistor, (germanium instead of silicon) they managed to install it the wrong way around, its not fitted pin-out correct. Still I guess we can be generous, it was at least a PNP 🙄
I’m not surprised the N1500 has problems with the sync pulse, a new BC158 will be fitted shortly. This now has me worried about other work that may have been carried out, methinks more close studying of the various PCB’s is required to spot any past repairs and their accuracy
Replaced the incorrect transistor with a correct BC158, results are very disappointing!
The result now is I don’t get any video playback output from tape whatsoever. 🤬
The VCR is receiving an input signal from the test generator (test card F) and is outputting that signal to the AV channel on the TV (E-E). However whereas before when play was pressed the signal was interrupted with the PB output from the tape, now the signal is not interrupted, the tape is playing but all I get is the non interrupted test signal output.
- Now is this related to the change of transistor and/or perhaps other things that might have been messed with in order to get it working with the CV7004 transistor.
- Now the correct transistor and associated voltages are present has this now taken something else out up stream.
- Or has something else now just coincidentally expired, nothing to do with what has just been done.
- Has a wire (a-la-g6)worked or broken loose.
I’ve checked for loose wires and have not found anything untoward. TS851(IC) & TS852 are candidates for no video PB.
I’m tempted to put the old transistor back to see if the player returns to the state it was in before (unlocked video PB output). If after putting the old CV7004 back in it still does not have video output then something else has occurred. If video output returns then this will indicate otherwise.
This one is not going to give up without a fight, all fun and games!
Forum member TVj0n74 mentioned checking if like the N1700 the N1500 has a switching fault. Jon was on the right path after a little further studying of the circuit, followed by investigation of the hardware I think I’ve found the cause of the problem with play back, it might be SK401. The switch has a long thin paxolin board imprinted with copper tracks. At the end of each paxolin board is a metal cap with a protruding bar. This bar is then mechanically grabbed by two forks attached to the play and record keys. SK401’s paxolin board has started to de-laminate and has developed a curve so its fork cannot securely locate and grab.
I’ve soaked some Gorrilla glue into the spread de-lamination, greased a lolly stick and pressed it between two clamps in an attempt to straighten and strengthen. This must have been another weak point in the player along with the drum-cord loading. However I’m not certain this is the full extent of no play back until I can test, fingers crossed. Nothing to do with the CV7004 and everything to do with a coincidence of SK401 giving me grief!