Philips N2204 - Pristine but Not Playing

[Froomie G]

Hi, I am a Newbie from the West country.
I wonder if anyone can help me with a few simple steps to take to carry out with some basic troubleshooting on an N2204 cassette recorder ?
I took a punt on Ebay with a non-runner and was quite frankly blown away by
the superb pristine condition ( and gooey belts of course ) when it turned up. Looks to have been hardly used at all. Anyway, got it all cleaned up, new belts and off we go with fresh batteries. However, barely a deflection on the meter in the 'play' position, literally nothing apart from the tiny needle movement, a very faint hum. After a few minutes I give up and try the mains adapter, but again nothing apart from the faint hum. Taking the batteries out I note that they are now very warm and already have lost voltage after such a brief outing. So I might be good at cleaning goo, I do have a multimeter, but this electronic Philips chassis is new territory for me. So any guidance appreciated. Thank You.

[DMcMahon]

Hello and welcome to the Forum.

From your description it sounds like there is an internal electronic/electrical fault that is causing excessive load on the batteries/power adapter, like a short circuit or low resistance to the negative side of the electronics.

This assumes that the batteries are good, the power adapter is good and that the battery level indicator meter is good.

It could literally be anything like a failed component (transistor/resistor/capacitor) or a damaged/trapped wire etc, fault finding it may not be easy especially if you are not experienced.

The service information including electrical schematic is available as a purchasable download from the "Instant Downloads" from top right of the screen.

The first thing I would do is to measure the resistance across the +ve & -ve battery contacts with the batteries removed to see if there is a low resistance, low being a few Ohms or 10s of Ohms at most.

If a low resistance measured then would need to go through the circuit disconnecting/isolating as required to track down the problem.

If you follow the battery +ve line you will see that it goes through the Play switch (via the BU2 DIN connector) and connects through to three DC voltage lines/rails identified as A (7.15V), B (7.9V) & C (9V).

These have electrolytic capacitors C751, C754 & C755 respectively connected to them, the -ve side of the capacitors connecting down to ground/0V (denoted by the bold/thick bar line) which is the same connection as the -ve side of the battery. One of these capacitors could be shorted.

David

[Froomie G]

Thanks for your kind advice David.
Armed with multimeter I have done what you suggested.
With batteries removed the resistance across the battery terminals is high.
Like getting on for 0.5 Mega-Ohm.
When I engage the play or rewind switch then it immediately drops to nothing.
This I find a bit confusing with my limited electronic knowledge based on school physics but I presume that if the resistance of the circuit effectively drops to nothing then the batteries will discharge at a high rate and get warm, as is evidenced here.
Anything else worth an investigate at this point ?
Many Thanks,
Gavin

[DMcMahon]

Nothing specific at this stage just need to try and track down the source of the short circuit.

David

[Welsh Anorak]

You're making progress!
A key point (which I don't know the answer to) is whether the electronics are disconnected during rewind. If so, that makes fault finding easier as the problem is confined to the motor and its control circuitry. Does the motor spin nicely? I'd suggest disconnecting it and see if the short is still there.
My next port of call would be to measure the resistance of the electrolytic capacitors, if that makes sense, to look for a short circuit. You might need to desolder one lead of each to confirm. A good capacitor will measure hundreds of ohms, increasing rapidly to almost an open circuit.
Hopefully this won't be too hard a fault to find.

[ben]

The transport control on these operates a series of leaf switches, which supply the motor with volts in one or other polarity depending on winding direction. my guess is that there is something loose or shorting here. Inspect it all carefully in all modes.

[DMcMahon]

The DC supply feed to the 3 electrolytics (resistor tapped down after rail C) referenced in Post # 2 appears to be live all the time, taken from the top and bottom contact of the top changeover leaf switch, if I interpret the schematic correctly.

David