Re: Racal Dana 9916 Frequency Counter.
 

Have you looked at the data sheet for IC 1 (74247!) on the display board.

This may give you a clue as to what likely is wrong?


On digital circuits you never see sawtooth wave forms, especially not 12mV!

TTL is 5V or 0V.

What is the BI input (IC1 pin 4 on display board) for, and what does it do?

The data sheets will help you understand what is supposed to happen, and so you can work out what is wrong when it doesnt happen.


If you do not understand the data sheet (not everyone is experienced with logic circuits I know) I will be happy to go through it with you.

Re: Racal Dana 9916 Frequency Counter.
 

Good evening Peter, thanks for your reply, i have ordered some replacement 74247 led driver ic's, i have 7447, these are the older types, probably no built in protection or something, i will have to check the pinouts.
I have had the display board off looking for any sort of problem and fitted a socket for the new 74247 when they arrive.
Did you see the comment re damaged trace under a red dot of some marker pen fluid or something, this feeds IC1 but as i am unable to add a pic ( dont know how to) to show everybody the affected area i am not sure if it is a data line, all i can say for certain is that it goes to the edge connector feeding the display board.
snowy

Re: Racal Dana 9916 Frequency Counter.
 

The fact that the decimal points are all working is useful, because it proves that the driver of that part of the display is working. So Q28 (and circuits feeding that) plus the multiplexer transistors Q18 to Q25 are working.

IC1 pin 4 is the Blanking Input. It forces all display segments drivers (which are open collectors outputs) in IC1 to OFF when it is LOW. However you are measuring the odd voltage of 3.314V on pin 4, with 12mV of ripple on it. Its fed by 3 NAND gates type 74LS03 - these have open collector outputs, so to get a HIGH, its depending on R111 (2k2) to pull it up to 5V. So why are you measuring 3.314V? Something is pulling that voltage down slightly - perhaps a fault with the 74247, but you are replacing that anyway. And that voltage is high enough that it should not activate the Blanking function on IC1.

The TI datasheet I've looked at says the 74247 is electrically and functionally equivalent to the 7447A (whether that 'A' suffix is important I don't know).

The obvious test to do is to activate the Lamp test - when IC1 pin 3 is LOW, it forces all 7-segment drivers to ON, so you should be seeing all the displays with all segments on. The fact that you don't suggests that IC1 is dead - since we have already said that Q18 to Q25 are apparently OK. A scope on IC1 pins 9 to 15 would check this point - just in case you somehow have open circuit tracks - or open circuit resistors in 1R4.

If IC1 has failed, then the next question is likely to be why? That may not matter if the fault is cleared with a new 74247 in circuit.

Richard

Re: Racal Dana 9916 Frequency Counter.
 

Thanks for the info Richard, i have already checked the 'R' on the display and all values are correct, I am almost certain that I have a 7447 IC, so I'll dig one out and try that after a few more tests.

Please keep the advice coming gents, thanks to all.

Re: Racal Dana 9916 Frequency Counter.
 

Right Gents, some good news (for a change), i build Nixie and LED clocks when i am not playing with other things, to that end i have a number of nixie/led display driver ic's, so i dug out a 7447a ( see note from Richard above) and fitted that into the previously fitted ic socket, i was rewarded with a lot of 0's, so looking good, just have to wait for the correct ic's to arrive then i can re-assemble counter and give it a thorough check over.
So many many thanks to all that offered advice and suggestions. cheers, snowy

Re: Racal Dana 9916 Frequency Counter.
 

If I remember correctly the 74247 was the same as the 7447 but displays the 6 and 9 differently.

David

Re: Racal Dana 9916 Frequency Counter.
 

Snowy,

that's good news! I think it would be worthwhile though checking the voltages around that 7447A in circuit. Something caused that 74247 to fail (might be old age of course!), and there is at least one "odd" voltage - on pin 4. You measured 3.314V I think, which is neither a true LOW or HIGH. It would be worth checking with a scope to see what its doing now.

Also checking that all other pins are at either HIGH or LOW states - or have waveforms on them with those voltages.

Richard

Re: Racal Dana 9916 Frequency Counter.
 

Richard, no 3.314v voltage now on the ic, possible finger trouble measuring it or leaky ic.
Unfortunately replacement 74247 will not be here for a couple of weeks, supposedly a uk seller but i bet they come from China, so parentage is going to be doubtful!.

Re: Racal Dana 9916 Frequency Counter.
 

Shame Farnell have the £9.95 handling charge as they have the IC for £1.24

Re: Racal Dana 9916 Frequency Counter.
 

Hi Stephen, they have them available across the pond but £16+ postal charges makes them prohibitive, my ic's are from Bulgaria not China as previously stated however the proposed delivery dates are correct.

Re: Racal Dana 9916 Frequency Counter.
 

Good Morning Gents.
would it be beneficial to try and acquire the 5mHz ovenised ref rock to fit into this counter.
I have 1/2doz cathodeon ovens with 20mHz rock in, i will change that to 5mHz but is it worth the bother?
cheers
Snowy

Re: Racal Dana 9916 Frequency Counter.
 

Must admit, both the 9915 and 9916 I only ever saw them with the square xtal oven fitted.
Rob

Re: Racal Dana 9916 Frequency Counter.
 

Hi Robin, mmm, ok looks like i have to try and obtain an correct crystal oven from somewhere, thanks for your input, shame about the rallies, missing all the old faces and the natters.Snowy

Re: Racal Dana 9916 Frequency Counter.
 

Snowy

did you diagnose a fault on IC1 on display board?

What did you find wrong that means it needs replacing?

Did you read and understand the data sheet for the 74247?

Re: Racal Dana 9916 Frequency Counter.
 

Evening Peter, it must have been damaged by the small piece of lifted pcb tracking, it was shorting out on another.
As soon as i repaired the track and having confirmed that data was getting to ic1, i was rewarded with all the digits that had been awol.
so i then put a frequency from my 2022e into it and it was almost spot on, a little tweak and it was ok for a while, then it started drift, i now have a ovenised rock to fit into it ( when it comes from Jeremy.

Re: Racal Dana 9916 Frequency Counter.
 

What is the frequency standard fitted to it?

there are three options as standard;

Option 04A (9442) fast warm up ovened OCXO
Option 04B (9421) Precision OCXO
Option 04C (11-1254) TCXO

The TCXO was only specified when the instrument was to be used with an external frequency reference, but I have found them to be pretty good into VHF use, and not drift significantly once settled at temperature.
If you wait it will stop drifting and stabilise, unless it is faulty of course.

If it has the TCXO, then an ovened oscillator will improve its stability over time.

The OCXO's are specified to stabilize after 6, and 20 minuits.

Racal OCXO's are good!

Are you sure the 2022E is not drifting?

Re: Racal Dana 9916 Frequency Counter.
 

Hi Peter
The ref rock as fitted is a 2" square PCB having a trimmer for adjustment, works OK but I want something a bit more stable for when I setup my homebrew items or indeed do some repairs.

I have checked the output from the 2022E against another counter, seems to be OK, tongue in cheek. Snowy

Re: Racal Dana 9916 Frequency Counter.
 

Yes that is the TCXO, which is not really meant for accurate measurements. Only specified when the counter is used with external reference.

Re: Racal Dana 9916 Frequency Counter.
 

Thanks for the update Peter, i have a 'ovenised' rock coming from Jeremy later this week, looking forward to fitting it and having a stable counter, thanks for everybody's help in another successful repair. Thanks chaps and chapess's. must not be sexist huh ha ha.