Problem Switches on Philips N4510 - UK Vintage Radio Repair and Restoration Discussion Forum

BSABiker · 4th Aug 2017, 3:30 pm

Hi all,
I own a philips N4510 reel to reel tape deck which I bought in 1974. This was used until the early 1980's when I moved up to a Tandberg TD20a half track stereo machine. Recently I resurrected the Philips machine in order to transfer my library of 4 track stereo tapes to computer then CD. On switching it on nothing much seemed to be moving. Once I had taken the deck out of its case I discovered it was suffering the dreaded rubber goo syndrome! I have spent the last two weeks cleaning up the mechanics and replacing drive wheels/belts etc. Despite this on switching it on again all the touch switches now light up, but none of them operate or engage a particular function when pressed. Normally only the function switch pressed lights up until another switch is pressed, this turns of the previous function. Any help/ideas would appreciated.

TonyDuell · 4th Aug 2017, 6:41 pm

This is a faiirly common problem with these machines, and it has nothing to do with the physical switches. I have an N4510 and an N4450, and both suffer(ed) from it.

The problem is the control system flip-flops, which are on little PCBs plugged into the transport control backplane in the machine. In the N4510, there are 2 (identical) PCBs, each containing 3 flip-flops. The more complex N4450 (with autoreverse) has 2 PCBs containing 4 flip-flops each. The actual flip-flop circuit is much the same though.

It consists of 2 cross-coupled transistors as you might expect. But being Philips it's unconventional. It's a silicon NPN transistor (originally a lockfit BC147, replaced in later machines with a TO92 BC547, which is what I would now fit) and a germanium PNP transistor (AC128). The latter go leaky, and confuse things.

I have found that a silicon transistor can be used to replace them. I used 2N3906s in the N4510, but now thing they may be under-rated (as they directly control the deck solenoids) so will try something like a BC640 from now on.

Did this fault occur, though when you dismantled the machine to clean it? If so, I would check the 3 cables/plugs to the deck and the 4 wires to the PSU board (you have got them back on the right tags?). And make sure the plug-in PCBs are properly seated.

You are right, the belts in these machines turn to Evil Goo and it gets everywhere.

BSABiker · 5th Aug 2017, 10:56 am

Hi Tony,

Thanks for the reply. I had already read your previous thread regarding flip flop circuits in these machines, but wanted to check that this was the most likely problem in my machine. I note your comment about using an up rated transistor and will try to obtain these and effect a repair.

4th Aug 2017, 3:30 pm	#1
BSABiker Diode Join Date: Aug 2017 Location: Redditch, Worcestershire, UK. Posts: 5	Problem Switches on Philips N4510 Hi all, I own a philips N4510 reel to reel tape deck which I bought in 1974. This was used until the early 1980's when I moved up to a Tandberg TD20a half track stereo machine. Recently I resurrected the Philips machine in order to transfer my library of 4 track stereo tapes to computer then CD. On switching it on nothing much seemed to be moving. Once I had taken the deck out of its case I discovered it was suffering the dreaded rubber goo syndrome! I have spent the last two weeks cleaning up the mechanics and replacing drive wheels/belts etc. Despite this on switching it on again all the touch switches now light up, but none of them operate or engage a particular function when pressed. Normally only the function switch pressed lights up until another switch is pressed, this turns of the previous function. Any help/ideas would appreciated.

4th Aug 2017, 6:41 pm	#2
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,213	Re: Problem Switches on Philips N4510 This is a faiirly common problem with these machines, and it has nothing to do with the physical switches. I have an N4510 and an N4450, and both suffer(ed) from it. The problem is the control system flip-flops, which are on little PCBs plugged into the transport control backplane in the machine. In the N4510, there are 2 (identical) PCBs, each containing 3 flip-flops. The more complex N4450 (with autoreverse) has 2 PCBs containing 4 flip-flops each. The actual flip-flop circuit is much the same though. It consists of 2 cross-coupled transistors as you might expect. But being Philips it's unconventional. It's a silicon NPN transistor (originally a lockfit BC147, replaced in later machines with a TO92 BC547, which is what I would now fit) and a germanium PNP transistor (AC128). The latter go leaky, and confuse things. I have found that a silicon transistor can be used to replace them. I used 2N3906s in the N4510, but now thing they may be under-rated (as they directly control the deck solenoids) so will try something like a BC640 from now on. Did this fault occur, though when you dismantled the machine to clean it? If so, I would check the 3 cables/plugs to the deck and the 4 wires to the PSU board (you have got them back on the right tags?). And make sure the plug-in PCBs are properly seated. You are right, the belts in these machines turn to Evil Goo and it gets everywhere.

5th Aug 2017, 10:56 am	#3
BSABiker Diode Join Date: Aug 2017 Location: Redditch, Worcestershire, UK. Posts: 5	Re: Problem Switches on Philips N4510 Hi Tony, Thanks for the reply. I had already read your previous thread regarding flip flop circuits in these machines, but wanted to check that this was the most likely problem in my machine. I note your comment about using an up rated transistor and will try to obtain these and effect a repair.