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TonyDuell · 15th Nov 2017, 8:48 pm

A friend managed to get me an original Philips motor. Although it didn't look identical to the old one, it fitted perfectly, and seemed to work.

I then went through the electronics.... Firstly, never plug the Recorder Stop and Motor Stop modules into each others connectors. You will blow transistors if you do. Do not ask how I discovered this. Having fixed that, the motor seemed to work, but neither reel motor (original or replacement) would restart reliably if the tape got too tight for too long. A tweak of the tape tension presets cured that, oddly both needed to be turned to about the same position to get the right voltages as in the service manual. So it appears that the replacement motor is electrically the right one.

I had already replaced the leaky AC128s with 2N3906s. They are marginal, the pinch solenoid draws rather too much current and one of the transistors was going way out of saturation with a C-E drop of about 5V. This caused the control logic to get confused. I will fit some heftier transistors, but for the moment I have reduced the 2k7 base resistor (actually by paralleling it with a 2k2) which has helped. The machine will now work, play tapes, etc.

Two problems remain. One is cosmetic, the trim strip for the knob on the mains switch needs repainting. The other is that the pulley on the tape counter has a radial crack, for which the obvious solution is to turn a replacement. When it is slightly warmer in the garage...

Oh and one more hint. The N4510 is essentially an N4418 without power amplifiers. The N4510 manual on the web is not very complete. I recomend downloading the N4418 manuals as well. You need the N4510 manual for details of the audio circuitry, but the N4418 manual is a lot clearer on the mechanism and control sections.

15th Nov 2017, 8:48 pm	#3
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Philips N4510 reel motor A friend managed to get me an original Philips motor. Although it didn't look identical to the old one, it fitted perfectly, and seemed to work. I then went through the electronics.... Firstly, never plug the Recorder Stop and Motor Stop modules into each others connectors. You will blow transistors if you do. Do not ask how I discovered this. Having fixed that, the motor seemed to work, but neither reel motor (original or replacement) would restart reliably if the tape got too tight for too long. A tweak of the tape tension presets cured that, oddly both needed to be turned to about the same position to get the right voltages as in the service manual. So it appears that the replacement motor is electrically the right one. I had already replaced the leaky AC128s with 2N3906s. They are marginal, the pinch solenoid draws rather too much current and one of the transistors was going way out of saturation with a C-E drop of about 5V. This caused the control logic to get confused. I will fit some heftier transistors, but for the moment I have reduced the 2k7 base resistor (actually by paralleling it with a 2k2) which has helped. The machine will now work, play tapes, etc. Two problems remain. One is cosmetic, the trim strip for the knob on the mains switch needs repainting. The other is that the pulley on the tape counter has a radial crack, for which the obvious solution is to turn a replacement. When it is slightly warmer in the garage... Oh and one more hint. The N4510 is essentially an N4418 without power amplifiers. The N4510 manual on the web is not very complete. I recomend downloading the N4418 manuals as well. You need the N4510 manual for details of the audio circuitry, but the N4418 manual is a lot clearer on the mechanism and control sections.