DF3380 Frequency  Counter - Page 1
Forum section: electronics / testgear

author: PinheadBE
author_rank: Regular Contributor
timestamp: September 02, 2023, 10:59:38 pm
content: Hi,DF3380 was a cheap frequency counter sold in Europe, end of the nineties. See picture.I am looking for:- its specs- its user manual- its service manual, if anySchematics and calibration procedure highly welcomeThanks

author: J-R
author_rank: Super Contributor
timestamp: September 03, 2023, 10:15:20 pm
content: I doubt there is a calibration "procedure", other than just adjusting a single trimmer for the oscillator. Photos of the back and inside? Does it work?

author: PinheadBE
author_rank: Regular Contributor
timestamp: September 03, 2023, 11:29:39 pm
content: I will receive it tomorrow and will test itI guess this is a super simple model without any processor, only logic chips

author: coromonadalix
author_rank: Super Contributor
timestamp: September 04, 2023, 01:48:33 am
content: must be based on intersil frequency counter chips, there was tons of theses designshttps://www.qsl.net/iw2grf/pdf/icm7216.pdfthere was an 40 pins dip too icl7226https://pdf.datasheetcatalog.com/datasheets2/17/177840_1.pdfonly adjustment was a 10mhz clock sourcecheck goldstar, some kenwood ....

author: PinheadBE
author_rank: Regular Contributor
timestamp: September 04, 2023, 09:08:06 am
content: I suspect it's even simplier than that.There is no function button, it seems to measure only frequency.Also, the "Display Test" button is a dead giveaway of a 7447 BCD to 1-digit driver logic chips ....In 6 hours from now, I will have the answer.About the internal oscillator, it surely will not be something of great precision, and I plan to invest a couple of bucks to change it into something in the range of 1% precision. I don't need more precision, since this will not be my primary counter, but a secondary oneEDIT:I stand corrected: the Intersil chips you mentionned do also have a Display Test function.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: September 04, 2023, 01:19:50 pm
content: In my experience, the simple oscillators in these old units are pretty stable, Sometimes the adjust cap gets wonky though. The Xtals are well aged.You can attach an external oscillator to some easily, others require a modification like a BNC input on the back. Then attach something like a GPSDO.

author: PinheadBE
author_rank: Regular Contributor
timestamp: September 04, 2023, 09:17:29 pm
content: Finally, to my big surprise, it's a ICM7216D that runs the show...This version of the chip functions only as a frequency counter.I tested it, and was astonished by its precision: less than 0.1% error at 10 MHz with a 2 V p-p signal.... Incredible.3 crystals on board: two of 10 MHz, and a third I couldn't read completely the frequency, but it was somewhere in the 3 MHz rangeOther chips:- 74LS04- 74S196N- MC10116P- An 8-pin DIP chip on the VHF input, with markings stripped off (WHY?), but its designation seems to end with "40". Probably a VHF amp and divider ?- 7805 regulated linear PSI tested in the 10 MHz range and got a stable and precise readout until almost 12 MHz (2 V p-p). Quite impressive !In the 60 MHz range, i was able to get the readout until 60 MHz, since my siggen cannot go higher than that.All in all, for a couple of bucks, I think it is was a bargain !Now, on with the hacks !First (and maybe only) thing I would like to do is to protect the VHF input against too high input voltage > 3 V (as mentionned on the case).Since I do not have the schematics nor the specs, I do not know at what extense this input is already protected or not....The 8-pin chip mentionned abode is mounted on a small PCB directly soldered on the rear of the VHF input BNC. I will try to reverse-engineer it, but it will not be easy because of that soldering.To get a first lead, do anyone know of a VHF amp/divider (maybe 1:6 or 1:2 followed by 1:3), in 8-DIP, dating the nineties, and whose designation ends with "40" ?

author: coromonadalix
author_rank: Super Contributor
timestamp: September 05, 2023, 12:57:20 am
content: the 8 pins buffed ic must be a prescaller, there was a very popular one at theses period, i think its no longer available ...

author: PinheadBE
author_rank: Regular Contributor
timestamp: September 05, 2023, 09:11:35 am
content: Probably not, but if I'd know its specs, I could maybe find a replacement, just in case, because that 3V p-p limit on this input scares me a bit...

author: coromonadalix
author_rank: Super Contributor
timestamp: September 05, 2023, 10:32:52 am
content: wellthe intersil ic's are 10Mhz max input ... in your part list you miss a prescaller to go beyond 10Mhz ........i would be sure it is a prescaller / frequency dividerlike MB506, B5551, SP8660 ....

author: PinheadBE
author_rank: Regular Contributor
timestamp: September 05, 2023, 11:49:44 am
content: Yes, there is a prescaler. I meant "No, it's probably not available anymore"It's a 8-pin DIP chip with markings erased, but it seems the reference ends with "...40". (See picture)Do you know of such a chip ?There is a switch to change the range between 10 MHz and 60 MHz.So, the prescaler could be a 1:6 divider, but that switch could also switch the quartz frequency (there are 3 different crystals, see above)

author: coromonadalix
author_rank: Super Contributor
timestamp: September 05, 2023, 02:15:22 pm
content: could try the saliva trick on it? or something to macro zoom on it and try to read it ??I would say if the thing works, dont play too much in it, if you have an xtal adjustment you could do some trimming ....butain't broke don't repair it lolllyou have some GW Instek like the GFC8131 or some FC-XXXX models who share some resemblances .... you have to search schematics with ICM7216D as the brain

author: PinheadBE
author_rank: Regular Contributor
timestamp: September 05, 2023, 02:56:45 pm
content: Saliva and microscope helped me to see the "...40", but nothing more.Thanks for your suggestions: I will further Google

author: edavid
author_rank: Super Contributor
timestamp: September 05, 2023, 03:45:07 pm
content: Most likely they used a divide by 10 prescaler so they didn't have to switch the ICM7216D clock. You should be able to confirm that.Plessey made some suitable parts, and if I squint at the photo it looks like the part number might start with SP. Look for an old Plessey databook.If it is a divide by 10, you could always replace it with something like a 74AC160.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 05, 2023, 05:18:09 pm
content: same i thought i saw some SP ...... toobut the only one who ends up with 40 are the SP8640 series but haven't seen dip 8 variant, they are 14-16 pins ...Mb 501 or MB506 where popular