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Old 15th Mar 2021, 8:27 pm   #41
collisr
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Default Re: Philips N1500 - can it be tricked?

Hey Philip.

Been watching the thread with interest. I have renovated about 5 N1500s in the past 2 years and I too have varying versions of your problem (based on your YT video)

I found the head eddy brake voltage was hardly ever above 0.5v and often 0v. I swapped AC motors, tried different sizes/sources of belts BUT... I did find these machines reported to work okay at a friends house (!)

I have still not concluded the problem but starting to think it is the value of mains voltage and/or frequency where I live. I was considering setting the N1500 to 220V to see if that made a difference.

I haven't had a chance to test this theory, but just a thought

Rob
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Old 16th Mar 2021, 4:22 pm   #42
The_Archiver
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Default Re: Philips N1500 - can it be tricked?

Rob, thanks for another slant on this.

Right from the get go with this machine, I did wonder whether to select 245V or 220V on both of the rear rotary switches, and settled on the former. Mains voltage where I am is averaging 235V, so if testing was to be tried on the 220V settings, would it be reasonable to expect no circuit/motor damage, especially if the machine were to be used only for short periods?

Will either ponder for a while before taking the plunge, or keep waiting on the oscilloscope arrival for checking servo pulses first...

Philip
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Old 16th Mar 2021, 6:41 pm   #43
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Default Re: Philips N1500 - can it be tricked?

I honestly don't know Philip. I've not had the time or courage to try so far.
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Old 18th Mar 2021, 4:49 pm   #44
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Default Re: Philips N1500 - can it be tricked?

Finally got around to disconnecting the eddy brake for the capstan, and upon testing, tape now runs fast but the picture sync disturbance reduces in frequency. The audio actually seems to be even better than before, as there is no intermittent wow.

So, is this pointing to a mixture of mechanical and electronic problems? Still waiting on an oscilloscope arriving so canít yet make checks on the latter.

Philip
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Old 2nd Apr 2021, 12:03 pm   #45
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Default Re: Philips N1500 - can it be tricked?

Quote:
Originally Posted by The_Archiver View Post
Owen, these two photos may help, showing you the plastic gear required and where it slides on to.

Philip
Thanks very-much for those pictures, that I've only just seen.
It seems the small plastic slide-on gear was missing from mine, so will have to see about buying a re-made replacement type.
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Old 14th May 2021, 6:26 pm   #46
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Default Re: Philips N1500 - can it be tricked?

After several weeks of not doing very much with the N1500, have now dived back in. Electrical checks will begin after an oscilloscope is [finally!] due to arrive next week, but in the meantime, have started dismantling mechanical items: the first is the reel disc assembly, with the coupling disc (item 130 in parts list) shown in the attachment.

The rubber brake block nearest the bottom of the photo has become slightly sticky and blotchy (the other three are fine), and has left residue against the inside wall of the ring (item 118) in which the disc sits. Platenclene is to be used on the pinch roller and idler wheel, but not sure if it would make any difference to the brake block. May need to remove that one altogether before reassembly and see what the result is. The brake blocks in a spare N1500 which I have, are all in a much worse condition.

Will keep updating as and when...

Philip
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Old 30th May 2021, 1:31 am   #47
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Default Re: Philips N1500 - can it be tricked?

Possibly final update: both the capstan and head drum drive motors were removed, cleaned, top and bottom bearings greased, then reassembled; very slight buckle in capstan brake disc sorted; idler wheel and pinch roller treated with Platenclene; all other relevant lubrication carried out.

The result? When switched on, the tape drive is now running whilst in STOP mode with a cassette inserted (that did not happen previously), and pressing START in this condition is fraught with danger of causing tape damage. Position of idler wheel has been checked and correct, winding friction items have been adjusted as per Service Manual, but to no avail. Non-functioning eddy current brake on the capstan? Switch/es not operating correctly during/at end of threading cycle?

It seems, and not just in relation to this machine, that I am simply making things worse, so, unless you folks have any more ideas, this N1500 is now a large paperweight until getting taken for recycling.

Gutted would be the best description!

Philip
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Old 31st May 2021, 1:56 pm   #48
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Default Re: Philips N1500 - can it be tricked?

The eddy current brake is not for braking to a stop, only for speed regulation (the motor runs a bit fast, the servo controls the brake to run it exactly right).
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Old 31st May 2021, 4:03 pm   #49
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Default Re: Philips N1500 - can it be tricked?

Thanks, Maarten. Have checked again all mechanical switches and interlocks and still cannot see anything which I have inadvertently reassembled incorrectly, but if itís an electronic problem, would that be allowing the tape drive to run at full speed from the moment of switch on?

The one thing noticed now at switch on (since reassembly) is that there is no hunting of the servo at all, so does that point to electronic problem/s?

Itís a [rude word] pain, but donít have the heart to do anything drastic with it.

Philip
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Old 2nd Jun 2021, 8:58 pm   #50
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Default Re: Philips N1500 - can it be tricked?

Canít seem to put this machine down, so earlier this evening decided to start checking the servo system as per the Service Manual, as there are evidently issues there resulting in reel drive when should be in STOP mode (all mechanicals OK).

First, following precisely the instructions in photo 1, the oscillogramme produced in photo 2 was more a saw tooth than square wave, however, part of the circuit diagram in photo 3 for servo control shows that it should be a saw tooth.

Second, R293 could not be adjusted far enough in either direction to obtain a wave period of 20ms, as also shown in photo 2.

Third, possibly using the trigger function incorrectly, it was not possible to obtain a completely stationary wave, but very nearly.

Adjustments and results posted will continue next with head servo.

Nothing to lose, plenty to gain.

Philip
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Old 4th Jun 2021, 2:20 pm   #51
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Default Re: Philips N1500 - can it be tricked?

Unable to do any more with this as I cannot understand how to use an oscilloscope correctly, and triggering in particular is just gobbledygook for me as I have trouble concentrating these days.

Machine and tapes will now be skipped, thanks to all who tried to help.

Mods, please close this thread.
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Old 4th Jun 2021, 9:40 pm   #52
Maarten
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Default Re: Philips N1500 - can it be tricked?

Please do not skip.

Also, I don't think the servo circuit would be at fault, as this only regulates speed through the eddy current brake. Not whether or not the motor is switched on.

Unfortunately I have only basic knowledge of those machines or I would have tried to help more.

If no one else can be of help, I'm sure someone will take the machine and tapes off your hands, as they're getting somewhat more scarce. If only to use the heads in his own machine when they wear down.
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Old 11th Jun 2021, 9:53 pm   #53
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Default Re: Philips N1500 - can it be tricked?

Maarten, the red mist lifted before anything impulsive was carried out.

Still going round in circles with it, but believe fault has been traced: the scanning pulse for the head servo was adjusted to stationary, but the scanning pulse for the tape servo is rolling over the sawtooth and cannot be made stationary via the relevant variable resistor (R259).

One servo board transistor so far has been found to be no longer working, many more to check. The waveform produced by servo head K7 is also not consistent with Service Manual so possible issue with head and/or distance between it and magnets on flywheel.

Thanks for your words of calming...

Philip
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