Vintage Heathkit Frequency Counter IM-2410 problems - Page 1
Forum section: electronics / testgear

author: vinlove
author_rank: Frequent Contributor
timestamp: March 17, 2020, 11:24:01 am
content: Hi AllThis IM-2410 seems working ok upto 10Mhz, but above that it reads out wrong. I was comparing it against my trusty HP counter, and the HP is spot on accurate on all the frequencies, but this IM-2410 reads about 2-3 Mhz low from above 10Mhz.Is this known problem? yeah, it is vintage counter, so it will have some problems, but just wondering if this could be sorted easy and simple, or is it something more sinister stuff going on in the set?

author: duak
author_rank: Super Contributor
timestamp: March 17, 2020, 07:27:36 pm
content: I have one of those things but don't use it much. Mine seemed to work OK but it never triggered as well as the hp or Tek counters I've used. I recall that the power supply design was marginal, see:https://www.eevblog.com/forum/repair/heathkit-im-2410-frequency-counter-power-supply-problems/Could it be as simple as the power supply voltage dropping as more and more digits are displayed?

author: vinlove
author_rank: Frequent Contributor
timestamp: March 17, 2020, 11:25:27 pm
content: I was suspecting the bad caps? Because the old caps always go bad.But it is very accurate from 100hz to 10Mhz. It is just after that, it reads about 2-3 Mhz lower than it should.I was also suspecting one of the chips / ICs?It is shame, because the set is very nice looking and I love the red LED lights of the freq. display.

author: duak
author_rank: Super Contributor
timestamp: March 18, 2020, 01:08:35 am
content: Well, the design is simple but I suspect it was designed more for a ham shack. Check out the power supply. You'd be surprised what weird things could happen if it's too high, too low or has ripple on it.Do you have a schematic? I'd think that something in the input circuit has gone blinky. I would check to see that the emitter of Q4 has a squared up version of the input and stays reasonably square as the frequency increases.

author: vinlove
author_rank: Frequent Contributor
timestamp: March 19, 2020, 11:09:02 am
content: Found out something with this Frequency Counter.When the source or input voltage is over 0.6V DC, it reads correct all the ranges.When it is 0.6V DC or lower, it will read 2-3Mhz lower than correct frequency over 10Mhz.My HP frequency counter reads correct even 0.1 or lower on all the ranges.

author: Grandchuck
author_rank: Super Contributor
timestamp: March 19, 2020, 05:27:01 pm
content: 0.6 volts is roughly the forward bias on an emitter-base junction. If the bias circuit has failed, then external bias will turn a device on. Look at biasing components and coupling capacitors. Do you have a schematic?

author: vinlove
author_rank: Frequent Contributor
timestamp: March 19, 2020, 08:31:19 pm
content: No, I don't. Maybe it will be in the internet?Do you reckon the coupling capacitors needing replacement? rather than looking into the power supply?It runs very hot, but then so does my HP FC.Checking it over in more detail, on some freq. higher than 40-50Mhz, it needs 2-3V DC from the source to work properly.What kind of input voltage do high to medium quality frequency counters work to in average?

author: Grandchuck
author_rank: Super Contributor
timestamp: March 19, 2020, 11:10:31 pm
content: Q1 could be the culprit (see the attachment). Its drain might be open. A gate to source path could allow external dc to turn on the next transistor. The input seems to be dc coupled. Normally, the next transistor (an NPN BJT) would be turned on by Q1 providing a path to the dc supply (12 volts?). It is a horrible picture, but all I found. Perhaps you can do better.

author: duak
author_rank: Super Contributor
timestamp: March 20, 2020, 12:28:50 am
content: Try this link:https://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Heathkit-IM-2410-Schematic.pdfFor the manual (no schematic)https://archive.org/details/HeathkitIM2410FrequencyCounterRegarding sensitivity, the manual says it's on the order of 25 to 50 mV. The manual has a small section on troubleshooting.What are the voltages on the D & S pins of Q1?Since you're there, what voltages do you see on +5V & +12V?

author: vinlove
author_rank: Frequent Contributor
timestamp: March 20, 2020, 10:51:42 am
content: Great links, thank youI have not opened the Heathkit Freq. counter yet. I was just doing a few test readings with it and other freq. counters side by side.I also have this vintage frequency counter by nameless Japanese company, and it is for Ham Radio shack too, I think.It is also reading properly when the input voltage is over 1V DC on over 10Mhz, and over 0.3V under 10Mhz.What is the Q1 transistor? Is it still available for buying in good price?Would it have been blown off when the previous users input some over voltage into the IM2410?

author: Grandchuck
author_rank: Super Contributor
timestamp: March 20, 2020, 01:51:45 pm
content: C1 could be shorted or leaky (nice to have a readable schematic). And, Q1 could also be bad as mentioned before. I'd check all the input components as a large applied signal in the past might have damaged several. And, as always, verify all supply voltages early on.

author: vinlove
author_rank: Frequent Contributor
timestamp: March 20, 2020, 02:34:41 pm
content: Yes, and it is a really nice document with good diagrams. I can see where +12V must come in.What is the Q1? Which transistor is it? Is it still available for purchase?

author: Grandchuck
author_rank: Super Contributor
timestamp: March 20, 2020, 02:40:14 pm
content: https://www.ebay.com/p/20003946151?iid=254091768427&chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=254091768427&targetid=883510870202&device=c&mktype=pla&googleloc=9012267&poi=&campaignid=9250237609&mkgroupid=93913847756&rlsatarget=pla-883510870202&abcId=1145977&merchantid=101689129&gclid=Cj0KCQjw09HzBRDrARIsAG60GP-NGi4M2ByvQ1IxnBnjtEvS47_qZN1Tee7AKw52R7s8aVgJj4Iv23YaAmc2EALw_wcBI am often reluctant to buy semiconductors this way but have had some success.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 20, 2020, 04:43:12 pm
content: Q1 is an RF JFET. There are several newer types available. Getting the right threshold level may be a little tricky, even with the original type.The tricky part today is finding types in TO92 / TO18 or similar THT case. Worst case one would have to use a SOT23 case with added legs.The supplies would be one of the first points to check. Old carbon resistors (especially high values) also tend to drift quite a bit.

author: vinlove
author_rank: Frequent Contributor
timestamp: March 21, 2020, 09:56:40 am
content: Seems plenty available in cheap price.https://www.ebay.co.uk/i/191840307381?chn=ps&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&itemid=191840307381&targetid=878161781224&device=c&mktype=pla&googleloc=9046980&poi=&campaignid=9437867654&mkgroupid=94751713814&rlsatarget=pla-878161781224&abcId=1139366&merchantid=113417885&gclid=EAIaIQobChMI2sSxw6ar6AIVh63tCh38gA9rEAQYAyABEgIgZfD_BwEHere too,https://www.ebay.co.uk/i/174206029212?chn=ps&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&itemid=174206029212&targetid=879157198036&device=c&mktype=pla&googleloc=9046980&poi=&campaignid=9437867021&mkgroupid=95526236133&rlsatarget=pla-879157198036&abcId=1140486&merchantid=6995734&gclid=EAIaIQobChMI2sSxw6ar6AIVh63tCh38gA9rEAQYBCABEgLAn_D_BwE