74196 chip in Frequency counter

[april]

Sorry for the delay. I was bogged down moving house-ie my boat

The voltages are

Pin 1     0.008 
Pin 2     0.6 F
Pin 3     1.4 F
Pin 4     1.3 F
Pin 5     1.4 F
Pin 6     0.014
Pin 7     0.015
Pin 8     4.76
Pin 9      1.100
Pin 10    1.6 F....Flashing 
Pin 11    4.0
Pin 12    1.3 F
Pin 13    4.0
Pin 14    0.010
Pin 15    4.74
Pin 16    0.004

When I say flashing I mean the voltage is changing on about a half second cycle and the value given is the highest seen on multimeter. I don't have a scope

 

[dr pepper]

I've lived aboard my boat a couple of times, I use it now at weekends and hols.
I have a sort of mobile 'shop that I use at work/foreighners/on the boat etc, part of which is a little thandar crt 'scope, it'll run on 240,120,12,24 or batteries, have a look on ebay they usually go cheap.
I also have a 12v solder iron, usefull I dont have to run the engine to get 240 to use it.

 

[Timescope]

Hi april, welcome back.
Please indicate the part number of the device you measured. Pin1 of the display is the top pin on the right when viewed from the back (inside the unit). Please post the voltages of the display and Q12, MSM561RS.

Timescope

 

[april]

Thats Q12 Not what I would expect
Didn't measure the display-There would be no voltages on it except for the decimal point which works OK
Its a new display and I have tried a few working displays in that position and they don't work

 

[Timescope]

First, your pin numbers are incorrect : your "pin 16" is actually pin 8, Vcc 5v (4.76v). Lets use your pin numbers. Pins 1, 2, 3, 4, 5, 14 and 15 drive the display segments. The 4.0v at pins 3 and 5 means that at least two segments should be working. If none are working, either R806 is defective or it is a connection problem as the display is new. I posted earlier that you should check for continuity between R806 and the display pins and to check for a hairline crack where the two boards are soldered together.
The display is common cathode. Check that the replacement display you fitted is also common cathode.
Timescope

 

[Dean Huster]

April, let's jump back to page 1, post 1 ... the beginning. Are you expecting to use this as a common frequency counter for hobbyist/experimenter use? If so, you're in for a rude awakening. This "counter" is actually an optional digital frequency display unit for a piece of Yaesu radio equipment. It's interpreting the master oscillator output and doing all sorts of weird things to compensate for trhe oscillator's weird frequency as well as the various amateur radio bands to which the main unit is switched. To use this as a "regular" frequency counter would take extreme modifications to the unit, including a complete rework of the gate circuit, adding a preamplifier/signal conditioner, adding a power supply .... just too much. Now, if you have it attached to the companion radio equipment, that's another story entirely. If so, then we're on the right track.

 

[Timescope]

Hi Dean, april has a boat (post #21) so he probably needs it for his radio. Any idea where we can get data for MSM516RS seven segment display decoder ?

Timescope.

 

[april]

Hi both . last time I looked I was a she. but that can change quickly these days I am told .
The counter is attached to my Yaesu FT7B which is attached to my 52 Ft Ketch which is attached to Port hacking Harbour last time I looked too. That can also change quickly and often does.

The counter comes in handy to tell me what frequency I'm on before I transmit as I hate the dial that comes with the VFO.

Timescope- my appologies , I put the top marker upside down while measuring . Its difficult to get at the chip when its powered up without shorting bits to earth. I have corrected the pin numbers above and I am working on tracing those three pins above 4 Volts looking for the fault . I have hit each pin on that counter line with a melt and set approach to no avail so I will continue . I have also done a melt and set on all the display board solder joins to no avail.

When I took those readings the frequency was at 14,300 MHZ so its the 4 that does not show so there should be voltage on 5 pins including the decimal point or maybe 4 if the decimal point is otherwise driven?

 

[april]

I've lived aboard my boat a couple of times, I use it now at weekends and hols.
I have a sort of mobile 'shop that I use at work/foreighners/on the boat etc, part of which is a little thandar crt 'scope, it'll run on 240,120,12,24 or batteries, have a look on ebay they usually go cheap.
I also have a 12v solder iron, usefull I dont have to run the engine to get 240 to use it.

You prompted me to go look at ebay and I saw a couple at under a hundred which will do to 40Meg..neat
I think a 12V iron is obligatory on any boat with a cabin isn't it?
I have a 6KVA generator for my freezer and welder that puts out 12V of course and try to stay with 12V rather than 24 . my radar runs on 24 unfortunately and these cordless tools definately run better and longer on 18V. so Im reconsidering .

 

[Timescope]

Hi april, to display "4" there should be voltage on pins 2, 3, 8 and 9 of the display. Please post the voltages on the resistor array pins, R806.
A picture of the solder side of the counter board would help me to give you specific points to check.

Timescope

 

[april]

Thanks , have hit a low at this stage . There are no voltages on the incoming lines to the resistor bank
From the end closest to the display 28,26,44,24,22,180,125,20 millivolts . Set up as before so I know I should have voltage on 4 of them . Now the tracks on the board run under the MSM561RS chip so I can't get at them directly without removing the chip. I'll do a photo in the morning but I have had it for today. Thank you for your patience with me .

 

[april]

With a fresh start I set up the dead display and another to display 7 .
That means at least 3 pins should have 4 V odd on them

I found no voltages on the faulty display line which compared to the correct display line so I have concluded that the fault is either the MSM561RS or the chip before it the 74LS196 and I'll check them next and replace them I suppose if nothing else come up.

It is strange that none of the segments lights even though I have confirmed power and ground connections are OK for both chips and all the resistors are good . All the joins are melted and resoldered and the only sus ones are the vias which I hav'nt checked properly. Is there a control line before these chips which could be out? Continuity checks seem to be OK through to the display

I have taken a poor photo of the board bottom with the camera I have available but I dont think it will be needed anyway now

 

[Timescope]

Hi april, we are almost there. You will need to find a way to set up the unit working in the position shown. Set the unit to the same conditions in post #21 when you listed the voltages. Check the voltages I have indicated in the attached "Test points". The brown areas indicate where you should scrape the green resist coating to expose the copper and re-solder.
A picture is worth 1GB so you could right click the image and "open with" paint to add text etc to it.

Timescope

 

[Timescope]

Is there a control line before these chips which could be out? Continuity checks seem to be OK through to the display

I do not think so. I have attached a snapshot of the relevant part of the schematic from the manual and added some colour to make it easier to understand.
I can not find the datasheet for MSM561RS but the connections are as follows:

Qa, Qb, Qc and Qd are the inputs (the count outputs from the 74LS196) pins 5, 4, 3 and 2 respectively.

The outputs to the display are pins 6, 7, 9, 10, 11, 12 and 13.

Pin 1 is the latch enable input.It is common to all the MSM561RS so this is not the problem as the others work. You can check for continuity between pin1 of Q12 and the others.

Pin 14 is open and pin 15 is tied to 5v.

The other two pins left are ground and +5v.

How did you measure continuity to the display, between which points?

Timescope

 

[april]

OK will get back to it in the morning with luck.
I found the diodes are connected inpairs except for first and last . All checked ok
Continuity was checked from either side of the 330 Ohm resistor to the display pins and then the other side back to the pins of the MSM561RS.
So this has confirmed the lines you speak of removing the solder from. There are no voltages on the display pins or the resistor pins or the MSM561RS except for input pos line now so it changes . Anyway I will get the voltages at the points you mention and do the solder points and clean back anyway so Ill post back when able . Thanks very much for spending the time Timescope.

 

[Timescope]

Hi april, sorry for the late reply, I was repairing a batch of 15 computers .

Do the other digits still work properly? Select various frequency bands on the FT-7B to verify that the first digit (tens of thousands) changes. This will confirm that the 74LS196 is ok.

I suggested earlier that you set up the counter to work without the metal chassis so you can measure the voltages under the board. You could solder a wire to the ground of the circuit board and wrap the other end around the negative probe of your meter so you will have one hand free and a solid ground.

I have also been looking into the possibility of invalid data at the input of the MSM561RS. Some display decoders blank the display when the input data is invalid (greater than 9 , binary 1001) like 4511.

The 7447 decoder has a RBI (ripple blanking input) pin that blanks the display when it is L (logic 0) and the input is zero (LLLL). This removes leading zeros for example, 14.5 is displayed instead of 00014.5.
This may be the function of pins 14 and 15: pin 14 is open and pin 15 is H (5v) for Q8 to Q12, pin 14 is grounded and pin 15 is open for Q13 (tens of thousands).

I would be my pleasure to get your counter working because equipment like this lasts for years unlike the modern micro-controlled disposable equipment.

If you have two transistors and light emitting diodes, you can build a simple logic probe that would make testing easier. Use red and green leds.

Timescope

from **broken link removed**

 

[april]

You sound busy.. You are right . This old radio and this counter has been around since about 1985 I think , maybe earlier
The radio has had the heat sink modified to replace the finals with larger and puts out an easy 100 watts. I decided late last year to get new displays because they had been misbehaving and I had been looking for them and found them one day at Vetco in the states. Turned out only one of the originals was indeed faulty when I breadboarded a test setup. The new displays are much brighter though and I have 5 spares.The salt air is not kind to electronics and most of my gear is soaked in Lanolin spray and grease. I once used lanolin grease on my battery terminals and electrons would not pass through it . I could get no power.

All other digits are displaying fine. The first digit changes as it should
Switching it on and setting it up as you suggest from the back I have 4 volts on 2 pins on the MSM561RS....8 and 15
On the 74LS196 I have 3 pins with 4V on them 1, 13 and 14

I later tested the display segments with 4V supply ,limited to 20mA, to each resistor input and all lit up fine. Continuity is good from each pin on the MSM to the display. I later wondered if I should have done this but repowering it showed it still worked the same.The chip can only have transistor switches I suppose so nothing would flow in the MSM561RS

I have a logic probe somewhere in one of my bins (plastic lidded bins stored everywhere). I'll find it.
I don't understand why the voltage has changed from those in post 21 Voltage on 8,11,13 and 15.I'll change the frequency a bit later and watch those pins because thats the only thing that has changed

 

[Timescope]

Hi april, I am back from defective hard drives, memory modules etc.

I thought lanolin was for skin care etc until I looked it up and found that is rated at 70kV. Sheep are well insulated

The experiment you did with the display indicates that the MSM561RS is defective: the display is working and the 74LS196 is ok because it is able to drive the next counter.
We now come to the hard part, removing an ic from a double sided pcb. Care must be taken to avoid lifting the pcb traces under the ic on the top of the board or damaging the through hole connections. The technique used will depend on the soldering equipment at your disposal. What do you have?

I would advise that you order spare ics for the FT-7B as well as the YC-7B. The part lists are in the respective manuals.

Do you have any ics available that we could use to improvise in the meantime until you obtain the replacement parts?

Timescope

 

[Timescope]

Hi april, I am back from defective hard drives, memory modules etc.

I thought lanolin was for skin care etc until I looked it up and found that is rated at 70kV. Sheep are well insulated

The experiment you did with the display indicates that the MSM561RS is defective: the display is working and the 74LS196 is ok because it is able to drive the next counter.
We now come to the hard part, removing an ic from a double sided pcb. Care must be taken to avoid lifting the pcb traces under the ic on the top of the board or damaging the through hole connections. The technique used will depend on the soldering equipment at your disposal. What do you have?

I would advise that you order spare ics for the FT-7B as well as the YC-7B. The part lists are in the respective manuals.

Do you have any ics available that we could use to improvise in the meantime until you obtain the replacement parts?

Timescope

 

[april]

Soldering wise not much . a 12 V and 240V soldering iron ,solder wick -some very old quickchip which might be useful here.
However I will order a chip and get it here first. Another method will be to cut the chip out with a dremmel and cutoff wheel.
There is enough room to resolder the new back on top

Not likely to have any other plausible replacements.
I saw your other posts on TV screens and TV chips . If I can help let me know -not the screens but the chips might be cheaper to Australia