Philips N4450 Reel To Reel Tape Recorder Capstan Motor Repair? - Page 1
Forum section: electronics / projects

author: Chris56000
author_rank: Frequent Contributor
timestamp: December 10, 2023, 04:42:13 pm
content: Hi!Finally, after many years trying, I have finally been able to procure my own Philips N4450 HiFi Tape Recorder – every one for sale has been snapped up by wassocks with bottomless C.C.'s, or the sellers want obscene prices for them - £1500 for one example, and they retailed at £237.50 UK List Price in 1972 when it came out!However, I fear my machine may have a faulty Capstan Motor as I couldn't hear it running when I tried the machine – this motor is designed to run all the time and it is a known failure point!The Capstan Motor is a 4–phase Hall Generator type driven by two special little tiny Philips Hall ICs within the motor assembly, which are not available separately, and they drive four BD135 transistors that switch the motor–coils across a +26 V supply via a d.c. speed servo in a separate discrete component module!My question is, is it possible to use two SS49 Hall ICs mounted at 90° switching four transistors, e.g., BC846 etc., in a circuit similar to that given in the Philips Equivalent Circuit for the Hall IC, which I append to this post?There's tons of room in the recorder, and I'm happy to design another PCB that can be soldered onto the motor pins – this motor is similar in size to the small DC cassette player ones, but it has twelve pins, four for the motor phase coils, one for the coil common, another four for the switching transistor bases, and three for the supply pins!Note that its NOT necessary to provide sinusoidal drive – the motor is switched like the coils in a stepper motor, but it runs in continuous rotation, NOT like the steps of a printer motor, etc!There is NO need for the motor drive circuit to be reversible as the tape deck mechanical arrangements cater for forward and reverse playback!Chris WilliamsPS!All the available chips and modules I can find are for 3 phase B.L.D.C. motors, and this one is four–phase!. . .I've additionally attached a pic of the motor board, the Vintage Radio Forum Member who posted this released it "Creative Commons 2.0" so it's freely shareable!

author: moffy
author_rank: Super Contributor
timestamp: December 10, 2023, 09:35:51 pm
content: Before attempting this redesign have you measured that the coils L1-L4 have reasonable resistance values and are not either short circuit or open circuit and that the motor spins freely by hand?You should check your supplies also that you have +26V and +21V, that TS703 is enabled and working and R1 is 100R.

author: Gyro
author_rank: Super Contributor
timestamp: December 10, 2023, 09:49:08 pm
content: Quote from: Chris56000 on December 10, 2023, 04:42:13 pmYou haven't said what you have measured on the (presumably variable via the speed servo) +26V supply? I would put a fault there before Hall sensors.

author: Chris56000
author_rank: Frequent Contributor
timestamp: December 11, 2023, 07:56:03 pm
content: The machine does light up all the meters and lamps, and I can hear rustling and frying noises from the speakers, (so it's certainly not completely missing from the power supply circuits!) so I'll have a look tomorrow whilst my friend is at work and report back!Chris Williams