Pride TF-1000 freq. counter/clock info needed

This was a high-end accessory, sought after when it was new 45 years ago. Doesn't look so terribly special now.

The digits are only lighted one at a time. Switching circuits feed the desired pattern of 7 segments into all the digits wired the same. But since only one turns on at a time, this saves a lot of wires. Called "multiplexing". The digits flash on, then off in sequence fast enough to cause flicker fusion and makes them appear to be illuminated all the time. The digit on/off patterns for the clock come from the fat 24-pin MM5314 chip.

The digit pattern for the frequency counter comes from another fat chip, the one marked "7208".

A set of 3 chips marked "4016" serve as the traffic cops. Either one or the other of those two fat chips feeds control voltages to the digits, by way of six NPN transistors Q11 through Q16. They serve to switch only one digit on at a time, the turn the other five off. The 4016 chips alone can't deliver enough drive current to meet the needs of the LED digits. The six transistors each provides a current boost to one digit at a time.

A problem that is only seen while the radio is transmitting points us to the frequency-counter side of this setup.

The diagram doesn't indicate which 4016 chip powers the left-most digit. Has to be caused by something that is NOT shared between clock and counter modes.

That chip is on the list of suspects.

The 7208 frequency counter chip is long obsolete and hard to find. It feeds into the 4016 chip that drives that left digit.

But those are the two things that seem most likely. The 4016 (diagram won't tell you which) and the 7208.

Everything else associated with that digit is shared by clock and counter modes both.

73

For that matter, rotating them from one socket to the next would move the problem to a different digit.

I have a stack of these I need to unload. Just haven't gotten a 'round tuit'. I won't devote the time to trying them out, they just gotta go.

73

Kinda narrows it down to the PNP transistor Q16. Schemo says it drives the common cathode for digit 6.

Did finally ditch all my TF1000 junkers on fleabay.

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dss56 said:

a bear to get the parts out of double sided plated through holes..

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Best labor saver there is to clip the leads from the part. Melt the solder while gripping the naked leads one at a time. Sucking the solder from a hole without a component in it lead is far easier, and no risk of ruining the plate-through sleeve.

The more leads a part has, the more labor this will save you.

It's the only way I'll remove a DIP package.

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dss56,

you should also replace those three electrolytic caps.

if they are on their way out (they have a lifespan) then they can take out other parts that are hard to find.

replace the caps and that counter will last a long time.
LC

loosecannon said:

that counter will last a long time.

Click to expand...

Until the 7208 counter and/or 7207 'companion' chip breathes its last for no reason.

It was incredibly popular for low-cost counters 40 or more years ago. Was used in literally dozens of products. Does a find job until it doesn't. I pulled those parts out of the pile of TF1000s we sold on fleabay. Only one of the 7208s was good out of five. Had another few counters that used this chip. The pattern was that it would work great until it didn't.

There is more than one revision of that chip, and the companion chip has to match the 7208 revision you use. They don't mix and match.

Here's hoping it lasts another 48 years.

Oh, and he's right about those electrolytic caps. Getting to where I just take that for granted and won't remember to point it out.

73