Racal Dana 9916 Frequency Counter.
 

good evening gents, have just purchased the above frequency counter as faulty spares or repair.
so far i have checked the voltages according to the manual and all are ok.
Q6 (ztx550 pnp) has 4.84v on both base and emitter but just 0.384v on the collector, replaced with new trannie, just the same, something beyond it dragging it down i suspect or is it (Q6) just a switch that should have the same volts on each leg if everything is ok?
pin 14 ic31 has just 0.384 rather than the 5v or so on it fed from Q6!.
lots of tants ( some blue types) mainly buff coloured, are these as prone to failure like the blues. no magic smoke or burnt areas visible.
Display shows a couple of dots and thats it.
I do have the manual so i can follow the circuit.
any and all help would be much appreciated, snowy

Re: racal dana 9916
 

I would check those tants.
I have had red and green ones as well as brown go short circuit.
If they are on a biasing circuit they just take the rail down.
If there is enough current available they just let rip.

Re: racal dana 9916
 

OK - so you have the manual so you can follow the circuit. Not sure the rest of us do though! If you would like helpful comments, then please post at least the schematic (and parts list if values aren't on the schematic).


Richard

Re: Racal Dana 9916 Frequency Counter.
 

The manual is on the KO4BB archive, they seem to be limiting downloads so I couldn't view it last night.
Scroll down to Racal Dana 9916 Frequency Counter Service Manual; http://www.ko4bb.com/getsimple/index...uals&dir=Racal

David

Re: Racal Dana 9916 Frequency Counter.
 

Q6 seems to be part of the channel select circuit, if I'm following it correctly it switches the +5V supply for channel B when B is selected, similarly Q13 does the same for channel A.
Check C15, C25, C26 for shorts? The +5V also goes to the L.F multiplier option board (if fitted).

David

Re: Racal Dana 9916 Frequency Counter.
 

David, Rich and Refugee, many thanks for your advice, i have changed a number of tants with 'normal' electrolytic's as the are just for decoupling, i injected a 10 mHz signal into it and followed it as far as i could, nothing found wrong, so i went to the display, voltages are fine, signal on my scope from the LED drivers, thru' the resistors up to the board connector, voltages appear ok as well. I cant for the life of me think that all the 7 seg's have died in one go. had to get away from it for a while, i have another go probably tomorrow, thanks for all the advice / suggestions so far, keep them coming please.

Re: Racal Dana 9916 Frequency Counter.
 

As you say above, it's unlikely that all the 7-segment displays have failed at once. More likely it is something common to all of them. It could as simple as a power supply issue, or possibly either the 7-seg driver (that drives each digit in parallel), or the multiplexing strobe signals, that select each digit in turn. Or, worst case, it could be the large LSI chip.

Re: Racal Dana 9916 Frequency Counter.
 

Having finally accessed the schematic, here's my immediate thoughts on your initial post.

1. Q6 is a power supply switch to the B channel amplifier and AGC system. Channel selection is described on page 4-3 of the manual.

2. Q6 is a simple switch. It is controlled by IC13d, a NAND gate. When that gate output is high, then Q6 will be off. When it is low it will be on. The purpose of Q6 is to increase the amount of current that gate IC13d can control.

3. You measure 4.84V on Q6 emitter. The schematic says it should "+5V". According to the test procedure on page 5-4, the +5V rail should measure 4.95V +-0.15V, so it can fall as low as 4.80V and still be OK. This looks fine.

4. You say the base also measures 4.84V, which means IC13d is high. That means the Q6 is off, and so it will not be conducting.

5. So why is the collector measuring 0.384V? It should - theoretically - measure 0.00V because Q6 is off. My guess is that there is some leakage back through an IC somewhere, which is receiving voltage from elsewhere in the system. Its probably OK - and I suggest looking elsewhere before chasing this one.


My conclusion is that this bit of the circuit - the B-channel amplifier - is nothing to do with the display being blank. Not sure why you homed in on this at all. Your measurements do not suggest a fault around Q6.

So the fault is that the display is blank?


Richard

Re: Racal Dana 9916 Frequency Counter.
 

Take a step back from it for a short while, and do'nt dive into bits of circuit randomly.

The heart of the 9916 is IC4, which is the counter, gate, and display multiplexor. This is a custom chip, so be careful around it.

It also handles most frequencies in the counter.

So I would start there and find out exactly what is not working.

The schematic gives a good description as to what each pin does, so follow that.

1 Do you have the 10MHz reference on pin 5?
2 Can you see the input frequency from front panel on Pin 22?
3 Are you seeing the gate pulses on pin 19?
4 Is there a 1MHz output on pin 6?
5 Is Vref OK?
6 Is there 10kHz on pin 7?
7 Is there any display data being clocked out of pins15, 16, 17 and 18?
8 do inputs 8, 9, 10 change state with frequency switch?

After making these initial tests you can then decide where the fault(s) lie, and start a logical diagnosis.

Also what happens when you select lamp test? All digits should show 8. Does just one show 8, or still just dots. Decimal points are displayed seperate to the digits.

After checking report back what you found, and should be able to guide you to next stage.

Re: Racal Dana 9916 Frequency Counter.
 

If the display is blank, apart from a couple of dots, then the place to home in on, is the display itself.

To make sure this isn't just "finger trouble" from not setting controls right, try going through the "Segment, decimal point and self check" test, section 5.15 on page 5.6 of the manual. And then tell us what you get?

If that test fails, then if you have not checked the +5V rail that is on the emitters of Q18 to Q25, then please do so now. Its probably OK, because you say there are these couple of dots that are lighting up, suggesting some voltage is getting to the 7-segment displays.

After that, I think you are going to need a scope to get into the nitty-gritty of the multiplexed display system.


Richard

Re: Racal Dana 9916 Frequency Counter.
 

Tantalum caps. We have the late Les Lawry-Johns to thank for the "Blue" tants concerns. Reds, blues, buffs, all the same. I have had very few failed ones over the years (plenty in the Grundig TVs I worked on for years, NEVER a failure).
However, they seem to fail quite quickly if used in decoupling voltage rails, but ONLY if their voltage rating is too close to the voltage in the circuit.
Usually if one has gone short in such circumstances, there is a good chance its head is visibly blown off, or a black burn mark somewhere.
Les.

Re: Racal Dana 9916 Frequency Counter.
 

The tantalum caps might be suspect, but my view is that they are unlikely to be the problem. First reason is that many of them as just signal couplers - if they fail, they will just mess up the bias in that bit of circuit, and at the moment I can't see any affecting the display.

Then the few tants that are actually across supply rails are unlikely to be a problem, because a) there are no burn marks according to the OP, and b) the OP says the voltages according to the manual are OK. So it would appear no tants are currently taking out supply rails.

One possible clue about the display being blank is in clause 4.43, which says "The display is also blanked out in the event of the failure of the 10kHz synchronizing signal." Its failure ultimately puts 1 IC1 pin 4 to zero. You might start there, and see if that pin is in fact a zero - then work backwards if it is.


Richard

Re: Racal Dana 9916 Frequency Counter.
 

Well gents, that's a lot of info for me to assimilate, i will make notes and make a start in the morning, have done some of the suggestions but will do them all again, this time making notes, my grey cell is not what it was ha ha. Thanks ponce again to all.

Re: Racal Dana 9916 Frequency Counter.
 

Good afternoon Gents, ok this is what i have found after printing off all your advice, i will address it to all rather than individuals, hope you dont mind.
IC1 pin 4 has 3.124v on it, so that i think is ok.
IC4 pin 5 has 10mhz, pin 22 has front panel input on it, gate pulses on pin19, 1mHz output on pin 6, 10kHz on pin 7, pins 15 - 18 showing data pulses, inputs on pins 8 - 10 change with position of front panel switch, nothing happens when i select lamp test, only LED,s lit are the decimal point ( alters in conjunction with front switch), top led showing mHz. so thats what i have found today. over to you gents,TQ

Re: Racal Dana 9916 Frequency Counter.
 

IC1 pin 4 should be one of two logic levels - nominally 0V or nominally +5V. And I would expect from what the manual said it to be DC at one of those two voltages. So 3.124V looks decidedly suspect to me. Is there some waveform on that pin that your DVM is averaging to 3.124V?


Richard

Re: Racal Dana 9916 Frequency Counter.
 

Btw.
I have seen many english people write mHz for Megahertz
and I think it is irritating.

Normaly mHz is Millihertz and MHz is Megahertz.

...my only 5c comment

Peter

Re: Racal Dana 9916 Frequency Counter.
 

Richard, i was using my Fluke 73 for measurements. another check is in order i think.

Re: Racal Dana 9916 Frequency Counter.
 

As you have multiplexed signals on pins 15, 16, 17 and 18 then fault is with display de-multiplexor, or displays themselfs.

Probe IC1 on display section.

Can you see the multiplexed pulses on pins 1, 2, 6 and 7?

What is the status of the Blanking input pin 4?

Lamp test (pin 3) should be low but change when you select lamp test function.

Not shown in the schematic is the VCC and GND pins (16 and 8 respectively) so check for supply volts on them also.

Assuming these are all OK, then the next place to look is IC 23 and IC28.

IC23 should have pulses on pin 14, and A,B,C, and D (pins 1, 2, 8 and 9) binary counting when pin 2 and 3 are 0V (connected to the reset line).
IC 28 takes this binary count, and should output the corresponding line to select the digit to display.

It looks like the display supply is seperated from the dp supply, so make sure the 5V "A" supply is correct on the switching transistors. (a pair of Tants on it!).

Wouldnt concern myself with the input section untill the display section is working correctly. There may be nothing wrong with it.....

My philosophy is fix what you can know is wrong.

Re: Racal Dana 9916 Frequency Counter.
 

Good Morning gents
Thanks for all your help Peter, all checked out ok.
using a magnifying glass and head piece i found a red spot on the PCB about 1" from the front panel connector, under red spot was a very thin track that was broken and the broken end was stuck on the next track, repaired that but that wasn't the main fault, its looking more like IC1 on the display board a 74247, so now today's work is to remove the display board and do some checks on and around the IC.

Stand by for an update.

Re: Racal Dana 9916 Frequency Counter.
 

Good Afternoon Gents, right got my head in gear and had another go at the 9916 today. results as follows:
TRH01uk, i have 4.98v to each of the driver trannies, your suggestion was to check IC1 pin 4, its at 3.314v, your other suggestion checks out ok q1-Q5 appear ok.
MotorBikeLes, no sign of any burn marks or tants without hats.
Peterg0rsq. the checks you asked me to do have the following results:
Q1 to 4 and 6 yes
Q5 ? is that IC4 pin 11?
Q7 there is a 'sort' of waveform but it looks like mush compared to all the others i have checked out.
Q8 yes
The only front panel LED,s that are on are mHz, gate/charging and the decimal point which changes with the operation of the front panel switch.
now sorry but i forgot to include the author of the next set of observations but the results are as follows:
he suggests i probe IC1, multiplexed pulses on pins 1,2,6,7.
status of Blanking input pin 4, no signal but showing 12mv saw tooth type wave form
lamp test pin 3, changes state when test button pressed h/l.
Pin 8 shows 4.26v with respect to chassis, pin 16 show 4.18v with respect to 5v line.
now onto IC,s 23 and 28, i have pulses on pin 14 and a,b,c,d pins 1,2,8,9, pins 2 and 3 are at 0.106v
Ic28 is the same as IC23
Tants changed on switching trannies but no change, so they were probably ok.
finally just a list of the voltages on the test points:
TP2 23.45V ( SHOULD BE 24V)
TP3 4.91V
TP4 5.02V
TP5 GROUND
TP6 -4.2V
Here endeth todays observations
over to you gents..

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.