[time-nuts] time-nuts Digest, Vol 87, Issue 5

Sun Oct 2 17:11:32 UTC 2011

The counter has two channels.  Channel A covers audio to 100 MHz,
requiring a divide by ten above 10 MHz.  The timebase is 10 MHz.

The B channel has a divide by 256 binary prescaler.  The timebase
for the big IC is switched to 3.90625 MHz to adjust for the /256 prescaler.

Not the best counter in the world, but I only paid $40 for one in mint 
condition.
But I would like to find a schematic for it.

On 10/02/2011 07:32 AM, Dave M wrote:
>> Subject: Re: [time-nuts] TENMA 72-5000 Counter Mods
>> Message-ID: <4E882064.3020805 at omen.com>
>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>
>> I have a manual for the counter which shows the block diagram but no
>> schematic.
>> An ICM7226A does the logic.  The A channel has a 10 mHz clock using a
>> discrete
>> crystal.  The power supply uses a transformer and appears to be
>> linear.
>>
>> A BNC connector next to the crystals could be repurposed to a 10 mHz
>> input. A small cap connected to one of the crystal leads might do????
>>
>> On 10/01/2011 07:16 PM, Dave M wrote:
>>>
>>>> Picked up one of these today for $40.00.
>>>> Timebase to 10 seconds.
>>>> Supposed to use a 10 mHz timebase for channel A up to  100 mHz.
>>>>
>>>> Any experience with this counter?
>>>> How hard to make it use the 10 mHz from a Thunderbolt?
>>>
>>> Have no information on this counter, and assume that it's target
>>> audience is consumer electronics service shops. Need to ask a couple
>>> questions before making suggestions.
>>> 1)  Does the counter have a jack on the rear panel for an external
>>> time base, and a corresponding Int/Ext switch?
>>> 2)  Do you have a manual or, at least, a schematic for it?
>>>
>>> If the answer to Q1 is yes, then the solution is obvious... Connect
>>> your Tbolt to the External Time Base input, and switch to External.
>>> You might need a TTL level shifter to make it work.
>>> If you have the schematic for the counter, and can scan the area
>>> showing the internal oscillator, you might post it to a free file
>>> sharing service so that we can look at the circuitry and make
>>> intelligent suggestions.
>>> If no manual or schematic, then you'll have to do a bit of
>>> experimentation. Find the internal oscillator and scope the signal
>>> level and freq.  If it is, indeed, 10 MHz, then you'll need to find
>>> out if the TBolt 10 MHz output can drive the circuitry.  Is the
>>> oscillator output at TTL levels (0/5 volts)? If it is, then you'll
>>> have to build a level shifter to get the TBolt output to TTL levels.
>>> Temporarily break the connection from the internal oscillator and
>>> hook the TBolt in it's place.  Scope the TBolt signal and make sure
>>> that the counter circuitry isn't killing it.  If everything works,
>>> you're in good shape. If not, you might need to level shift the
>>> TBolt signal to TTL levels.  Find out as much as you can about the
>>> counter and come back to the list with more info.  We should be able
>>> to get you going.
>>>
>>> David
>>> dgminala at mediacombb dot net
>
>
> What do you mean by "The A channel has a 10 mHz clock using a discrete 
> crystal."?
> A signal channel in a counter doesn't have a "clock" as such.  The "A 
> Channel" handles the signal being measured.
> Also, for clarification, "mHz" signifies millihertz; "MHz signifies 
> megahertz.  Which do you mean?
>
> OK.. about the ICM7226A... This chip has provision for using the 
> on-chip oscillator or an external oscillator input.  Without a 
> schematic of the counter, I suggest that you get a copy of the 
> datasheet for the ICM7226A from http://www.datasheetarchive.com/.  
> Read and pay attention to the areas that discuss using the on-chip 
> oscillator vs. an external oscillator.  It's not as simple as 
> connecting an external oscillator through a capacitor.
> Compare the circuitry around the oscillator in your counter to the 
> schematics in the datasheet.  You'll probably find that they are very 
> similar in most respects, but only you can determine how similar, and 
> the exact steps you need to take to use a TBolt with the counter.  Use 
> your scope to look at oscillator signals around the chip and see what 
> they look like.  (TTL or analog)  That will help you determine what 
> you need to do with the TBolt signal so that the chip works properly.
>
> David
> dgminala at mediacombb dot net
>
>
>
>
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-- 
Chuck Forsberg WA7KGX N2469R     caf at omen.com   www.omen.com
Developer of Industrial ZMODEM(Tm) for Embedded Applications
   Omen Technology Inc      "The High Reliability Software"
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