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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 Sep 2018, 1:07 pm   #1
Tony_Sterling
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Default Philips N4450 tape recorder

have been using this machine regularly but alas one of the two fuses on the psu.has blown
Is there a usual suspect cap.or could it be any of them.ta tony
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Old 12th Sep 2018, 2:03 pm   #2
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Default Re: Philips N4450 tape recorder

It could have just been time for the fuse to blow . Have you tried refitting a fuse and see if it goes again ? If it hasn`t been re-capped at all though I would replace all of the electrolytics .
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Old 12th Sep 2018, 2:09 pm   #3
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Default Re: Philips N4450 tape recorder

Photos of the PSU please! If it's not been modified it may be that one of the rectifiers has failed. Worth just trying a new fuse (of the correct rating) first. I think it's 6.3 amps but check first.
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Old 13th Sep 2018, 9:49 am   #4
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Default Re: Philips N4450 tape recorder

have tried a replacement fuse but to no avail. so now i will have to remove case and hope i can still get replacements.
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Old 13th Sep 2018, 10:05 am   #5
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Default Re: Philips N4450 tape recorder

Yeah all the parts in there you can still get or a modern equivalent . I would start by disconnecting the power supply from the rest and working on that . Thats probably where the fault lies .
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Old 13th Sep 2018, 2:02 pm   #6
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Default Re: Philips N4450 tape recorder

You only need to remove the back cover. When I worked on these at Philips, the most common cause of the power supply fuse blowing was a shorted rectifier (BY164). There are two in parallel in both sections (so four in all). The mod was to parallel two more with each pair. You can probably find a more modern rectifier with a higher rating rather than paralleling four.

Very rarely one of the large smoothing caps failed. However after 45 years it's worth checking the caps as well.
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Old 15th Sep 2018, 4:37 pm   #7
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Default Re: Philips N4450 tape recorder

have just exposed the psu. i notice the by164 rectifiers are piggy backed on each other. does anyone know what equivalent i could install to save repeating this manoeuvre.
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Old 15th Sep 2018, 8:24 pm   #8
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Default Re: Philips N4450 tape recorder

Well firstly, are the rectifiers actually faulty? If you have piggy-backed rectifiers, it sounds like the mod has already been done....no point in replacing them just for the sake of it. Have you got pictures available yet?

It's worth noting that once the mod was done, there were no further problems....that was 45 years ago though.
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Old 16th Sep 2018, 1:00 pm   #9
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Default Re: Philips N4450 tape recorder

I would think with the mod being done already that they are ok . I have you tested them ? Do you need some assistance testing them ?
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Old 16th Sep 2018, 4:15 pm   #10
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Default Re: Philips N4450 tape recorder

would like some assistance in testing them. have been trying to send two pics. of the psu .but no luck there either. can they be tested in situ have tried resistance testbut nothing conclusive
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Old 16th Sep 2018, 4:25 pm   #11
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Default Re: Philips N4450 tape recorder

Ok to test the rectifier in situ , Check the following

Check you have AC coming in on the middle pins and you have DC going out on the + and - pins (the two outer ones) .

Tell us what voltages you get both AC and DC please .

If you DONT have DC but you have AC , then you will need to remove it for further testing and I will explain how to do that if that case arises.

Meter set to AC for the AC test
Meter set to DC for the DC test
Probed either way around for AC on middle pins
Red probe on + black on - for DC test outside pins
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Old 16th Sep 2018, 4:51 pm   #12
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Default Re: Philips N4450 tape recorder

I just remembered that the fuse is blowing . DUH , so you are going to need to pull the rectifier if you want to test it properly Look at this pic

Set your MM to diode test .
The red dots are the red probe and the black dots are the black probe .
A tick means you SHOULD get a reading
a cross means you should NOT get a reading .

Readings are NOT important only if you DO or DO NOT have one so no need to write them down.

Basically on the middle pins you should have NO reading either way around , and on the left and right pairs , you should have a reading one way , but not the other .

Let me know if you dont understand .
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Old 16th Sep 2018, 9:39 pm   #13
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Default Re: Philips N4450 tape recorder

heres a better version on the pic ..i drew the last one in a hurry ..lol
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Old 23rd Sep 2018, 1:05 pm   #14
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Default Re: Philips N4450 tape recorder

Thanks very much for the info. great drawing! have been in hospital so only getting back into the workshop very soon.IM more used to valves than diodes,slippery little gritters they are.
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Old 4th Oct 2018, 4:15 pm   #15
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Default Re: Philips N4450 tape recorder

One of the rectifiers was blown, have taken it away, and replaced it with a new one, which is 5Amp, but it is still blowing fuse. Suppose now I have to pull out the caps.
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Old 4th Oct 2018, 5:20 pm   #16
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Default Re: Philips N4450 tape recorder

Quote:
Originally Posted by Tony_Sterling View Post
One of the rectifiers was blown, have taken it away, and replaced it with a new one, which is 5Amp, but it is still blowing fuse. Suppose now I have to pull out the caps.
I would isolate the supply board , so disconnect everything from it so that the power supply is the only thing thats going to be turning on when you hit the switch. See if is still blows the fuse , if it does at least you know the issue is on that board there somewhere. Which fuse is it blowing ?

edit ....this missing one I`m guessing ....I`ll have a look at the schematic ....

Edit 2 : Check the 2 diodes on the power board , if they are bad then that will blow the fuse ..

put the meter in diode mode , test one way , then the other way , you should get a reading one way , but not the other. Some times you can`t test them in circuit , some times you can , but I always say take them out , its far easier . Make sure you put them back in the right way round .

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Old 25th Oct 2018, 5:15 pm   #17
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Default Re: Philips N4450 tape recorder

At last its up and running many thanks to you Dave in Norfolk. there were total of five bridge rectifiers of which two were shorting out.I lifted of the pcb. some of the Caps they gave good readings on the resistance meter but on my low voltage neon light there was a slight glow. On finding the cost of replacing them iput them back and decided the tape recorder could go back down the tip if it did not work.but hey presto.alls ok.
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Old 25th Oct 2018, 7:08 pm   #18
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Default Re: Philips N4450 tape recorder

A bit off topic, see my hifi circa 1973 or 74. With my N4450 pride and joy
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Old 25th Oct 2018, 9:42 pm   #19
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Default Re: Philips N4450 tape recorder

Quote:
Originally Posted by Tony_Sterling View Post
some of the Caps they gave good readings on the resistance meter but on my low voltage neon light there was a slight glow.
Glad you got it working.

You can't reliably test electrolytics like that....as you've proved by putting them back to find it all working....if they were really faulty, you'd still have a problem. Some large value electrolytics may well show up some leakage with some testers. A proper bridge or an ESR meter is the only way.
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Old 25th Oct 2018, 9:50 pm   #20
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Default Re: Philips N4450 tape recorder

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A bit off topic, see my hifi circa 1973 or 74. With my N4450 pride and joy
Looks like you have a Leak Delta 70 there.....I'm still using mine with Philips 4-way speakers, a Philips CD player, a Marantz direct drive turntable and a Leak Troughline stereo tuner....and I'd quite happily put it up against a modern system. The tuner is the best I have ever owned.
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