Quiet Phillips N4308

[Martin Bush]

Hi all

I have a Phillips N4308 reel to reel which I have managed to get moving again thanks to replacing the belts. This involved quite a bit of goo removal - I keep finding it even now including under some of the metal work that operates the brakes. However that is almost a side issue now.

The problem I have now is that the machine is quiet. With the volume all the way up the sound is only at a very polite level. There is no distortion or crackling, it is just quiet.

I have tried cleaning the pots and track select switch, but that hasn't done anything.

The machine also hums - I am unsure if this is a fault or just the sound of the transformers etc.

To start with, I have two questions...

Out of the two service data sheets available up top, which is the best one to get? I am not proficient when it comes to using service data, so I am treating this as a bit of a learning exercise.

When I have the right/ best data, where should I start?

I have a meter, iron etc - but my experience of using them is quite minimal (well, of the meter at least).

Martin

[DMcMahon]

The 11 page one has more information but it does not have the main PCB component layout drawing that the 5 page one does, so for the relatively minimal cost I would get both myself.

I would start with a good visual of the electronics, wiring etc checking for anything damaged etc. Then check out the 6 DC supply voltages (rails A to F), if all OK then I would check the transistor voltages.

Ensure the Playback/Record head is really clean.

David

[Nickthedentist]

Hi Martin,

Are you attempting to play known-good, pre-recorded tapes, or its own recordings?

You could also try cleaning/exercising the record/play switch.

Cheers,

Nick.

[Martin Bush]

I have a tape that came with it plus two supplied by a forum member - none recorded especially for me, but they have recordings on. I have some official pre-recorded tapes hidden away which I may try (I just remembered about those).

I presume the one that came with it was recorded on this machine, but I can't say for certain. I've come close to throwing the reel out the window as there's almost too much tape on it and it drops off when trying to put it in place to play.

@Nickthedentist By the "record/ play" switch do you mean pressing the record/ play button(s) or going inside to physically clean?

@DMcMahon - I have previously cleaned the heads, capstan, roller etc, but there is no harm going back and redoing.

It seems to make no difference to the levels if the pressure pad is applied or not.

[Martin Bush]

I have tried exercising the play and record switches but this hasn't done anything.

The volume is still low. At full it is on what I would expect the volume to be at 2 (the numbers go up to 5). There is no distortion - it is just underwhelming.

So I will be downloading the service data and building myself up to go poking around with my meter

One thing I do want to try is connecting the machine to my hifi. I think the only way to do this is via the phones output - am I right? And to do this I need a slightly different DIN plug - known as a domino?

[DMcMahon]

Looking at the schematic pin 3 and/or pin 5 of the Radio/Phono DIN (Skt 1/BU1) will provide a line output, pin 2 as always being the screen connection.

David

[Martin Bush]

Thanks David.

Having tried a few things to rectify the volume last night I got to the stage where I was enjoying just listening to a tape - even at the low volume.

I decided to pack up and remove the tape reel... it was incredibly tight. So tight that it took the reel table off! I had managed to slightly over-tighten the screw which very slightly expanded the bit on the reel table you put the tape reel on. So there's a lesson learnt!

[Nickthedentist]

Originally Posted by Martin Bush

@Nickthedentist By the "record/ play" switch do you mean pressing the record/ play button(s) or going inside to physically clean?

Both. You really need to go inside and establish which levers move when you select record, and follow them to the actual switch on the PCB which they actuate. Apply some Servisol Super 10 sparingly, then go from stop to record to stop to record and so on, a dozen or so times.

[Nickthedentist]

Originally Posted by Martin Bush

I have a tape that came with it plus two supplied by a forum member - none recorded especially for me, but they have recordings on.

I would try making a recording. You should be able to feed a CD player or whatever into one of the DIN inputs.

[Martin Bush]

Cheers Nick. Having got it all back together I simply operated the buttons to see if that helped - it didn't. Of course I now have to go back inside to sort the reel table out so will have a proper go then.

[DMcMahon]

Originally Posted by Martin Bush

I have a tape that came with it plus two supplied by a forum member - none recorded especially for me, but they have recordings on.

Have you proven on another R2R that these tapes have good recordings on, i.e. not quiet, I know that it would be unlikely that they all have quiet recordings.

David

[Martin Bush]

I don't have access to another machine. However I have tried the one that was on when I got it, along with two from a forum member plus I tried a couple of stereo classical ones - proper commercial pre-recorded ones. All are quiet.

I actually don't know how loud this machine should be, but my dad has a version (a model one down the range) and says it's not quiet. On max I'd expect someone to say "Can you turn that up a bit more?"

It will take me a bit of time to get my act together to investigate further as I tend to do things in fits and starts when I have an hour here and there. However I have an idea what my next session will involve.

[Station X]

Have you cleaned the tape heads?

[dazzlevision]

I have experienced very quiet playback due to the “tin whiskers” effect internally shorting out the Germanium driver transistor (which drives the AD161/AD162 output pair). If my memory is correct, it’s housed in a square metal outer case and screwed (heatsinked) to the metalwork that the rotary controls are fixed to.

The small PCB in this model uses minuscule copper tracks and is a bit of a nightmare to work on.

Be careful if you try to remove the sliding part of the special Philips slider switches on the PCB - they should only be fully removed at one end without damaging the fixed part if not put back in the correct orientation. The official Philips service manual has guidance on this.

[Nickthedentist]

Originally Posted by Station X

Have you cleaned the tape heads?

That's a very good point which I took for granted

[Martin Bush]

I think I mention cleaning the heads somewhere above. I have done it twice now actually.

I am pretty sure it is something other than dirty heads.

[DMcMahon]

Martin did confirm at post # 4 that he had cleaned the heads and would do it again.

David

[dazzlevision]

Originally Posted by dazzlevision

I have experienced very quiet playback due to the “tin whiskers” effect internally shorting out the Germanium driver transistor (which drives the AD161/AD162 output pair). If my memory is correct, it’s housed in a square metal outer case and screwed (heatsinked) to the metalwork that the rotary controls are fixed to.

Driver transistor is TS6, an AC187/01. As per the official Philips service manual.

[ben]

Apologies for the delay in replying, Martin. The low sound is a common problem on these and is due to tin whiskers in the germanium driver or an output teansistor. You can work around it by disconnecting them one by one from the heatsink until full output appears. Adding a separate heatsink using a scrap piece of aluminium will enable you to use the plsyer if you don't feel able to solder in new components.

[Nickthedentist]

I never knew this problem affected these machines. Thanks Ben and Dave.