Marconi TF2430 frequency counter

[Techman]

I picked up one of these from a local junk sale a while back for a quid. It was faulty, but was an easy fix. I've just been to another electronic junk sale at the same place and picked up another one for a quid, as I thought that it would be good for spares for the one I've already got, should it ever need any, that is.

This second counter is slightly different in that it has the filter switch on the front panel. I had doubts that it was working when I noted that the case had been fitted back to front with the stand up foot on the rear, instead of the front of the case (case just been slipped back on the correct way round for the photo below). Anyway, it doesn't work. The display lights up and is actually brighter than the one in the working one, so that's one item that may be useful as a spare for the original one if this latest one isn't fixable.

As can be seen from the pictures below of the two counters, the first picture shows that with all push buttons disengaged, all the zeros light up but with only one decimal point showing on the far left, whereas on the working counter all the decimal points are showing as they should do. I've not made any particular checks other than to prove the fact that it doesn't count anything and there doesn't seem to be any signal from the internal oscillator at the socket on the rear. The only evidence of previous repair that I can see is the replacement of an electrolytic capacitor in the power supply.

Any pointers and suggestions welcome before I dive in, as it would be nice to get this one going if it's an easy fix. I fixed the last one (shown in the second picture) without any service information, but what I really need is a copy of the manual if anyone has a scan of it - I've searched and there's nothing out there.

[Station X]

In this thread WME bill indicates he has the service manual:-

https://www.vintage-radio.net/forum/...ad.php?t=83427

It might be worth PMing him.

[Techman]

Thanks Graham. I did see that thread while searching for information and was wondering whether to send a cheeky PM, but thought I'd post a thread and wait a day or so to see if anyone would offer the service manual. I've just checked and I see Bill is still active on the forum, so he may see this thread. I'll leave it a day and then message him to see if he still has the info. and doesn't mind sending it.

[G0HZU_JMR]

I've got a copy of the 2430 schematics for the main board, the display and the overall interconnections if you don't have them already? PM me if you want a copy.

I've owned one of these TF2430 counters for over 30 years and it has given great service. It has a nice display, is very sensitive and usually gives a stable readout even on weak signals.

Sadly, one of the LED segments has started to fail on mine so one of the segments in one of the digits is getting very dim now. Otherwise, it works great. I think I paid £15 for mine back in the 1980s at a radio rally which was a huge bargain back then.

[Techman]

Originally Posted by G0HZU_JMR

I've got a copy of the 2430 schematics for the main board, the display and the overall interconnections. PM me if you want a copy.

It has a nice display, is very sensitive and usually gives a stable readout even on weak signals.

Thanks, I'm glad of all the information I can get, I'll PM you.

Yes, I agree that it is a very nice counter and the working one I have works exactly as you say and I really like using it. It's actually my only frequency counter of this type, although I did buy another very strange one at the same sale that samples every five seconds and reads the much higher frequencies into the GHz range. It was sold as a 'microwave tester' and nobody knew what it was, including me at the time, but I thought it was worth a punt at a quid just for interest. It's a strange make and there's no real information on it 'on-line' that I can find, so I really ought to start another thread on it to see what others know about the model, although it seems to work perfectly. I actually forgot to switch my TF2430 off a while ago and it was left powered on for several days, not ideal for an old piece of kit which made me think about the life of the display. I do find it has a warm up time where it starts off very slightly high and then drifts down a few hertz or so.

[WME_bill]

Marconi TF2430 digital frequency meter 80Mhz.
I have the complete manual 1976. I don't press people to accept a manual, after I have mentioned that I have it, as I don't want to do something unecessarily. If you want a manual, then request it and I will scan or photocopy or put it on a CD as appropriate.
I have somehow collected perhaps a thousand test gear manuals, mainly Avo, Advance-Gould, Cossor, Dynamco, Hewlett Packard, Marconi, Philips, Taylor-Windsor, Telequipment, Tektronix, Solartron, SE Labs and a lot of smaller makers.
It includes most of the oscilloscopes on the UK market over the past 50 years or so, and also details of the instrument cathode ray tubes available. Useful if searching for an equivalent as a replacement.

Techman can take courage, I do not regard a request on this Forum as impudent, just another hobbyist struggling to keep a fine bit of old equipement working, and I'm glad to help. I will scan the TF2430 over the weekend.
Incidentally, I suspect it may be badge engineered, but I don't know the originator. The earlier TF2416 is the Venner/Malden 7737. Does anyone have any ideas.
wme_bill

[Techman]

Many thanks for your kind offer of a scan of the manual, Bill, it's very much appreciated. I'll send you a PM. I've had a look at the circuit that I got from Jeremy and I think the crystal oscillator will be the first port of call. I didn't get anything done whatsoever yesterday, but I've got some more pictures of the innards for reference and interest.

[Dickie]

Bill, I can confirm that the TF2430 series was a pukka Marconi Instruments designed and manufactured product. Who else used those dreadful through-hole "griplets" ? I worked on the mid-life upgrades of those products - those photos take me back a few years.

[Andrewausfa]

I was thinking it was a 'Venner' but only as it uses a very similar case and plastic surround to my AMF Venner 1000F 32mHz Nixie counter, which Marconi did a rebadge of. Clearly Richard was the man on the spot though

Andrew

[G0HZU_JMR]

The 7 segment LED blocks look different to my old TF2430. Have they been replaced at some point? Mine look original and have the pair of dots in a different location and the body of the blocks are painted matt black. The segments themselves look subtly different as well. Mine also has a different colour (main) circuit board and looks to be lacquered bare copper. Maybe mine is older? I think the IC date codes were somewhere around 1975 on my 2430.

[Dickie]

I think the TF2430 ran from 1974>78. The "laquered bare copper" appearance is just a different colour of solder-resist layer, brown rather than green.

[Techman]

I think this counter is like a later 'facelift' version and probably from the latter part of the production run as it has the addition of that front panel filter control that's found on later models to filter out possible higher frequency noise when reading lower frequencies. It also has a serial number plate on the rear, whereas the other working counter doesn't have one at all. I can't remember what colour the printed board was like on the other counter without taking it apart and I don't think I took any pictures of it, although it might be coming apart for comparisons, so we'll see then.

Well, I've checked the oscillator and it's working. I've scoped the waveform from the rear 'INT' socket of the working counter for reference and this is shown in the first picture below. The second picture is a bit pointless, but I've posted it to show the output, or lack of it, from the same 'INT' socket on the faulty counter with the same scope settings to show that there's definitely no output as such. The third picture shows the waveform at the crystal oscillator of the faulty unit itself, which I would say was perfect. The forth picture shows the waveform taken at the collector of TR10, actually taken at the junction of R61/R62, some slight distortion shown. The significance here is the fact that the oscillator is working but there's no output at the rear internal oscillator test socket, I'm a little bit suspicious of IC10, forth picture showing the significant part of the circuit, what do others think?

[Dickie]

The slight distortion is down to the oscillator output not being a sine wave. It's halfway to being a squarewave, and the bandwidth limitations of your scope and probe are modifying the wave shape. Assuming the collector of TR10 is swinging between 0V and 3V it looks OK. It should be a straightforward job to trace the signal through IC10 to the output socket to find the fault.

[Techman]

From the collector of TR10 to pin 13 of IC10 is the last place the waveform shown in picture four in the last post is seen, there's nothing coming out of that gate at pin 11 of the chip whatsoever. It does look as though it's the chip that's at fault, although I did wonder whether there was anything else going on, or not going on, around that chip, so I'm debating whether to open the other counter up to take some comparisons in waveforms. The chip is getting its five volt supply, which it would be unlikely not to, seeing as this is a continuous rail that supplies most of the rest of the circuitry on the board. Just out of interest, I fed in to the rear external socket with the switch in the appropriate position, the 10MHz signal from the output of the working counter, but this signal didn't get any further than pin 2 of that chip, so it does look like it's the chip that's totaled.

It's strange how you notice things that you hadn't noticed before when looking more closely at the circuit board. D21, one of the diodes in one of the two 12 volt bridge rectifiers is physically, but not electrically as regards the circuit, next to IC10 and on close inspection this diode has been replaced at some time in the past. The four diodes for this particular bridge are rather randomly spaced compared with the four diodes of the other bridge. On looking closer, it looks like D19 has also possibly been replaced, but all the others look to be original. This is where I spotted a mistake in the board layout diagram in that it shows two D21 diodes, however, I think the second one should actually be D20, the one being next to the IC10 chip is correct being labeled D21. It made me wonder whether there's any connection with the failure of D21 and the failure of the IC10 chip. Possibly someone was faultfinding the power supply fault
and their probe slipped off the leg of the diode and caught a pin (or two) of the chip, damaging it. The two diodes and perhaps that electrolytic mentioned earlier were then replaced, but the other fault was then there so the job was given up on and the case shoved back on the wrong way round and that was that. Perhaps the diode failed in such a way that it affected the chip in some way, although there's no damage to the board - and these diodes are mounted directly onto the board rather than on stand-offs, as are the diodes for the other bridge. Another possibility is that knowing where this unit came from and what its possible previous owners interest was, it could have possibly had the output of a high powered transmitter into one of the rear sockets, but this is all just speculation.

So I need to get hold of replacement DM74132N chip, I don't think I'll remove the one from the working counter to confirm, although it's certainly a thought, unless, of course there's any other thoughts on anything that's staring me in the face that I've missed or not thought about?

[HowMuch!]

Originally Posted by Dickie

Bill, I can confirm that the TF2430 series was a pukka Marconi Instruments designed and manufactured product. Who else used those dreadful through-hole "griplets" I worked on the mid-life upgrades of those products - those photos take me back a few years.

Pye did for one. I called them griplets, but I never knew if that was their official name or not. And this is the first time I have ever heard any one else mention them. Who made them, or where they came from I have no idea.

[Dickie]

Well that's a surprise. Googling reveals they were made by Berg Electronics.

[dave cox]

Pin 10 of IC10 needs to be 'high' to turn on the NAND gate when the clock goes high. I can't see enough circuit but I guess its pulled high by an R with the switch (SE) pulling it low to disable the internal clock (is it in the right position?). The schematic hints that pin 1, IC10 is floating in some cases which would not be so smart.

dc

[Techman]

Dave, are you sure you mean pin 10 as this gate section of the chip isn't used as far as I can see?

Do you mean pin 12?

I think the bit you can't see goes from pin 12 of the chip and through a 330 ohm resistor to the indicator (EXT STD) lamp drive.

The switch is in the correct position.

[TonyDuell]

A 74132 is the schmitt trigger version of the 7400. It's a quad NAND gate, same pinout as the 7400.

If the clock signal is going in on pin2, then the other input to that gate is pin1 and the output is on pin 3. What is the state of pin 1, therefore?

[karesz*]

Hello Richard,

you mean "The Connector Berg"_which in past 20-years is by Framatome?

Karl