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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 12th Mar 2023, 11:58 am   #1
tangoromeo
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Default Philips N4520 / N4522 Power issue ?

Hello All

I am new to the forum and also new to this machine. I have the N4520 model but guess this applies to N4522 as well.

I am no expert with electronics but have previously worked on an old Akai reel to reel and managed to sort out some issues by identifying and replacing faulty components.

The issue with the Philips is that when Play, FF or RW is selected there does not seem to be enough power for all of the functions to operate correctly, e.g. sometimes the audio plays but mostly there is just a hum (using headphones). I also sometimes get a hum on FF and RW. The counter illuminates normally in stop mode but does not count and sometimes dims in other modes. Often it seems there is not enough power to operate the capstan solenoid so that even though the brakes release the tape passes across the heads in an uncontrolled way.

I am aware of issues being logged with the increased power demand of the motors and wonder if it may be related to that?

Assuming it to be a power supply issue I decided to start with panel 5B which I believe is related to the power distribution to the machine.

The voltages on the schematic checked out (ish) and I also checked them with the machine in Play mode. The results were as follows:-

Capstan speed 9.5 cm/sec
Stop mode 36v=35.1v. Play Mode =21.3v
Stop mode 18v=17.5v Play mode =9.87v
Stop mode 24v=23.8v Play Mode = 19.8v

Capstan speed 19 cm/sec
Stop mode 36v=34.8v Play mode =21.3v
Stop mode 18v=17.3v Play mode = 9.85v
Stop mode 24v=23.8v. Play mode = 19.8v

Capstan speed 38 cm/sec
Stop mode 36v=34.4v. Play mode =21.2v
Stop mode 18v=17.2v Play mode = 9.8v
Stop mode 24v=23.8v. Play mode = 19.6v

I also checked the voltages in FF and REW mode as follows:-

36v initially fell to 12v and settled at 23v
18v initially fell to 9v and settled at 12v

I am unsure whether the stop mode voltages are ok, being slightly low or whether the play mode voltage drops are normal and to be expected.

I also checked the supply voltages to the other boards as far as I could and these seem to check out ok. The voltages to the ICs on the capstan speed regulator board were also within range.

I desoldered the electrolytic caps associated with Panel 5B including the large cans C901 and C902. All these checked out ok with a multimeter although C901 and C902 were above the range of my meter but they did pass a voltage and resistance test and also a capacitance test when connected in series with another capacitor.

I should also mention that I connected the machine via a simple dim bulb device which did not glow when the machine was turned on in to stop mode but briefly glowed brightly when play and FF / REW were selected but settled to a dim glow in these modes.

I am unsure what to check next and would appreciate any suggestions as to a methodical approach to tracing the cause of the issue bearing in mind my limited technical knowledge and resources
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Old 12th Mar 2023, 12:57 pm   #2
Michael Maurice
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Default Re: Philips N4520 / N4522 Power issue ?

I would replace C902 before doing anything else, you can get them from RS or Cricklewood

I couldn't find C901 on the circuit diagrams.
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Old 12th Mar 2023, 1:48 pm   #3
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Default Re: Philips N4520 / N4522 Power issue ?

Quote:
Originally Posted by Michael Maurice View Post
I couldn't find C901 on the circuit diagrams.
In a schematic I'm looking at, C901 (6,800uF) is on the +18 Volt rail just before F802 (2 Amp)

Lawrence.
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Old 12th Mar 2023, 3:35 pm   #4
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Default Re: Philips N4520 / N4522 Power issue ?

Ah yes, wa looking at a different circuit. in which case replace both capacitors.
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Old 13th Mar 2023, 7:49 pm   #5
tangoromeo
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Default Re: Philips N4520 / N4522 Power issue ?

Many thanks to both of you for your advice.

Yes, C901 and C902 are identical large can capacitors attached to panel 5B.

I have ordered replacements and will update the post when installed.

Thanks again

Trevor
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Old 14th Mar 2023, 6:30 pm   #6
tangoromeo
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Default Re: Philips N4520 / N4522 Power issue ?

Apologies to both of you - rookie error by me.

Whilst racking my brain as to possible causes of the problem it suddenly occurred to me that the dim bulb tester might be preventing the deck from drawing the current it needed. The deck is rated at 80W and I though that my DBT was fitted with a 100W bulb which should have been ok(ish). Anyway, turns out it was only a 60W bulb.

After satisfying myself with the DBT that there was no serious problem with the deck I started it up direct from the mains and hey presto! everything worked! Well, almost everything. The digital counter is illuminated but doesn't count and some switches are quite noisy but the audio is back and all the voltages on panel 5B are very close to the schematic values in all modes.

I think I will continue to replace all the capacitors associated with panel 5B as they must be nearing the end of their lifespan. I believe there is a thread on this forum relating to problems with the counter so I will be studying that, otherwise I will just work my way over the machine cleaning and testing.

Many thanks again for your kind responses to my initial post - I am sure I will need further assistance before I have finished with this machine and I will try to avoid overlooking obvious remedies next time!
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