EMRFD Message Archive 7553

Message Date From Subject
7553 2012-06-28 07:20:31 alan7114p Hal-tronix Frequency Counter Schematic
Does anyone have a copy of a manual or schematic for a Hal-tronix Frequency Counter? Our club received one during Field Day and it is not working. The digits light up, but the frequency is wrong and the displayed frequency changes at each time interval by huge amounts. I'd like to fix it but don't have much hope without a schematic.

Sorry if this is too far off topic.

Thanks and 73
Alan K6ZY
7554 2012-06-30 14:30:07 ha5rxz Re: Hal-tronix Frequency Counter Schematic
I've had no luck at all finding schematics for any of the HAL counters and you didn't mention the model number. A very old copy of QST dated 1981 showed that they had a 50A that worked to 50 MHz and a 300A which was good to 300 MHz.

Given the age of the counter it probably uses 74xx series TTL chips which are now almost impossible to obtain although a 74LSxx chip might work in its place if you find a broken one. From the way you describe the fault it could be any one of the following:

a) Power Supply. Check for 5.00 volts on the supply line then use a scope to confirm that it's ripple free.

b) Clock Crystal. There will probably be a 10 MHz clock crystal in there, make sure that it's oscillating properly

c) Input Amplifier or Gate Problem. More difficult to fix without a schematic.

d) Bad Connections. Dirty contacts
7555 2012-07-01 08:26:00 alan7114p Re: Hal-tronix Frequency Counter Schematic
Thanks, Peter. I should have mentioned in my post that I looked all over the unit for a model number and was unable to find one. I suspect that it was their first counter.

It does use 74xx series chips. Bad news that they are now unobtainable.

I will try the other things that you mention.

I also received a suggestion that it may be patterned on a design published in 73 Magazine. I have obtained copies of that article series and am going to try to trace out the circuit to see if it's a match.

I appreciate the suggestions.

73 de Alan K6ZY

7633 2012-07-24 08:25:07 alan7114p Re: Hal-tronix Frequency Counter Schematic

Your tips did the trick. Turned out to be a power supply that was inadequately filtered due to bad electrolytics. Changed them out and it seems to work just fine.

Thanks very much!

73 de Alan K6ZY
7643 2012-07-28 00:31:34 ha5rxz Re: Hal-tronix Frequency Counter Schematic
I've been doing this stuff since Adam was a lad, glad to pass