UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

TonyDuell · 27th Dec 2017, 5:23 pm

I've had it working, at least in playback mode. Some more comments :

The tracks on the amplfiier PCB are fragile, and as the board is densely packed it is too easy to press on components and break tracks when pulling the board out. Take care! You do not want to know how I found that out, suffice it to say I spent a couple of hours tracking down missing signals.

I had another intermittent problem, the unit would loose 1 channel which seemed to come back if I pressed on the body (not the contacts) of the head switch (on top of the direction 2 pinch solenoid). No, not bad contacts there. It turned out to be bad contacts on the 21 pin connector between the amplifier PCB and the base board which got disturbed when I pressed on the switch body!

If you are testing the bias/erase oscillator you must have the erase head connected (red plug on the Magnet Driver PCB). The erase head is in parallel with part of the oscillator transformer and thus reduces the inductance, increasing the frequency. With the head connected I get a reasonable 70-odd kHz. With it disconnected I get around 16kHz. And yes I did try to find a 'fault' before I realised what was going on!

-tony

27th Dec 2017, 5:23 pm	#4
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,213	Re: Uher CR210 versions I've had it working, at least in playback mode. Some more comments : The tracks on the amplfiier PCB are fragile, and as the board is densely packed it is too easy to press on components and break tracks when pulling the board out. Take care! You do not want to know how I found that out, suffice it to say I spent a couple of hours tracking down missing signals. I had another intermittent problem, the unit would loose 1 channel which seemed to come back if I pressed on the body (not the contacts) of the head switch (on top of the direction 2 pinch solenoid). No, not bad contacts there. It turned out to be bad contacts on the 21 pin connector between the amplifier PCB and the base board which got disturbed when I pressed on the switch body! If you are testing the bias/erase oscillator you must have the erase head connected (red plug on the Magnet Driver PCB). The erase head is in parallel with part of the oscillator transformer and thus reduces the inductance, increasing the frequency. With the head connected I get a reasonable 70-odd kHz. With it disconnected I get around 16kHz. And yes I did try to find a 'fault' before I realised what was going on! -tony