Thandar TF 200 Frequency Counter Help

[Don Philbin]

Hello all.

During this "Pandemic" I thought I would do some clearing out of old gear. I was digging through my attic/loft and came across my old Thandar TF 200 frequency counter, but for the life of me I can't find the power adaptor.  I know it takes 6 "C" type batteries for a total 9vdc, so I am wondering if anyone knows if the power adaptor would be 9vdc and also where I might obtain a mains adaptor for this? According to Google the batteries, if I used them, would last about 200 hours of use.

I appreciate any help anyone can give me on this.

Regards,
Don

[Fraser]

The service manual is to be found here....

https://k1.spdns.de/Vintage/Sinclair/Other%20Inventions/Other%20Electronics%20Products/Thandar%20TF200%20Frequency%20Meter%20Service.pdf

As can be seen in the schematics, the 6 x C cell battery sits across the input of the regulator but may be disconnected and replaced by an external power supply if desired. The TF200 is not designed to recharge the internal batteries using the external supply. The minimum operating voltage from the battery is 6V so you can consider that the minimum external voltage that will work. New Alkaline cells will produce at least 1.5V so a safe external supply voltage is at least 9V. Any regulated external power supply of 6V to 9V D.C. should be fine. From memory, the original power supply was 9V/200mA rated but I will see if I can confirm this. Current draw is detailed in the service manual and is a Paul try 43mA maximum. Due to the low current draw, I do not recommend a 9V unregulated power supply as they can output 12V or more when powering a light load.

Fraser

[Fraser]

This chap built a custom 9V power supply for his TF200 and other Thandar kit......

http://azurelectronics.com/Thandar%20Stack.htm

Fraser

[Don Philbin]

Thanks for the replies.

I just noticed on the circuit diagram that if using a 9v DC power adapter I need to make sure the outer is +9v DC, as most adaptors have the negative voltage on that and the centre is the positive.

I may end up making my own if I can't find anything suitable.

[CJay]

Hah, yes, the polarity on these is reversed to most normal PSUs, if you get it wrong it kills the ICM7216 chip and they're hard to get (you can get similar but then you'll have issues with decimal point indicators)