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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 26th May 2023, 10:27 pm   #1
electrostelios
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Default Philips N4418 another unusual problem

Hello. I am repairing a Philips N4418 tape recorder and while I have reached a good overall result, there is still a problem with the flip flops commands. all commands respond well but with a delay of some seconds. example from play to stop there is an instant reaction, but pressing play again all the indicator lights go out and the command does not repond. by waiting fiew seconds and pressing play again everything goes well. the same it happens with all commands. I thought there might be a problem with the transistors on the flip flop boards. so I replaced them all (BC147 with BC547 & AC128 with BC327) without success. the recorder works as it did before this replacement. Any help on what else could be responsible for this problem.
Thanks for your assistance.
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Old 27th May 2023, 3:41 pm   #2
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Default Re: Philips N4418 another unusual problem

Hello and welcome to the Forum.

I am not familiar with the flip flop circuitry operation on the Philips machines and can offer no useful ideas.

I see that Part 1 of the English Service Manual has quite a lengthy description of the Control circuity operation, also the flip flops operation and Part 2 of the manual includes a fault finding tree sequence for the control unit.

If you have not already seen these manuals have a look, they may help to trace what is occuring.

David
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Old 28th May 2023, 8:46 am   #3
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Default Re: Philips N4418 another unusual problem

Thank you so much David, I didn't know there was a second part of the service manual. I will find it and see how it can help me. it's my first time messing with such Philips circuits, even though I have great respect for its designs.

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Old 28th May 2023, 11:38 am   #4
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Default Re: Philips N4418 another unusual problem

Are the transport control switch contacts clean? If the trigger is not 'clean' then maybe this would explain the poor response.
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Old 31st May 2023, 10:45 pm   #5
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Default Re: Philips N4418 another unusual problem

I checked the contacts Ben, and they are fine. in these tape recorders, Philips built the electronic part something like an old computer, i.e. on top of a motherboard it has put about twenty micromodules, one for each function. the problem is that these modules interact with each other and that is where the problem lies. after all, all work is for strong nerves. I will be back.
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Old 1st Jun 2023, 8:50 am   #6
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Default Re: Philips N4418 another unusual problem

I worked on these decades ago when at Philips. Don't discount the rectifier(s) in the power supply (can't remember if there is only one or might be two in parallel) type BY164. On many occasions I had one section go O/C effectively making it halfwave rather than bridge. The power dips when a command is given and odd things can happen. Also check smoothing in case the caps have gone low capacity. If the rectifiers are suspect, there are probably modern (better) ones that can replace them. Alternatively use four separate diodes wired as a bridge.
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Old 1st Jun 2023, 9:12 am   #7
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Default Re: Philips N4418 another unusual problem

Good point about the rectifier, had this with Tandbergs.
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Old 1st Jun 2023, 4:10 pm   #8
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Default Re: Philips N4418 another unusual problem

Looking at two N4418 Service manuals (one English, one Dutch) they both show 2 separate bridge rectifiers (for different voltage outputs) both made up from 4 x OF194 discrete diodes.

So bear in mind if your machine does not have the one piece BY164 bridge rectifiers, it could have discrete diodes, but Sideband's advice still applies.

I cannot easily find any data information on the OF194 diodes ?

David
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Old 4th Jun 2023, 7:20 pm   #9
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Default Re: Philips N4418 another unusual problem

David, when i started restoring this machine the first thing i had to fix was its power supply. half of the circuit was off. three of the four ΟF194 rectifier diodes were burnt. unfortunately the damage had managed to extend to the flip-flops as well as the capstan speed controller modules.
I repaired the power supply with four 1N5401 rectifier diode I had on hand. while searching to find the OF194 rectifier diodes, I found the equivalent BY206 fast high frequency diodes, but they could not provide the right amperage, so I ended up with the BYW96E. and of course I replaced both electrolytes. now the machine it works, but it still has the problem with the logic controls. I am sure that the damage occurred from its power supply extended to other circuits as well.
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Old 5th Jun 2023, 9:35 am   #10
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Default Re: Philips N4418 another unusual problem

Check that your DC supply voltages are good and have no AC ripple present.

See what happens to the DC supply voltages when the tape trasport buttons are selected.

David
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Old 7th Jun 2023, 10:39 pm   #11
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Default Re: Philips N4418 another unusual problem

BINGO Problem Solved !!!

Many times a loose contact or a cold welding is something we don't think about. And yet therein may lay the problem. The specific machine is designed in such a way that you can separate the mechanical from the electronic part. The electronic part is then connected to the mechanical unit via multi-sockets on the right and left of the same chassis. So there was the problem. The contacts on the multi-sockets were loose and they made poor contact or not at all. They were repaired by closing the gaps and cleaned with contact cleaner and spinning brush.

Now everything is fine !!!

This old tape recorder extend its life for enough time.

Electrostelios
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Old 10th Jun 2023, 8:25 pm   #12
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Default Re: Philips N4418 another unusual problem

Good news, well done.

David
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