Adding an external reference input to a VC3165 counter? - Page 1
Forum section: electronics / testgear

author: rhb
author_rank: Super Contributor
timestamp: April 16, 2018, 02:08:49 am
content: Has anyone tried this? It appears to have a 12 MHz reference oscillator. Read by putting a scope probe on the trimmer, so not very accurate.I've got one of Leo Bodnar's nifty dual frequency GPSDOs so no problem feeding it 12 MHz.I'd like to configure it so that i can use an external reference, but still use the internal reference.

author: coromonadalix
author_rank: Super Contributor
timestamp: April 16, 2018, 02:26:47 am
content: some schematics to help, there is a thread here for this counter :https://www.eevblog.com/forum/testgear/victor-vc3165-counter-straight-outta-the-box/msg498745/#msg498745schematicshttps://www.google.it/search?q=vc3165+schematic&num=20&tbm=ischhttp://vrtp.ru/index.php?showtopic=24461https://www.electronicspoint.com/attachments/vc3165-jpg.5019/

author: rhb
author_rank: Super Contributor
timestamp: April 16, 2018, 05:00:13 am
content: Thanks. I used google to search eevblog.com and didn't find that thread. Of course, I rarely find the same thing on Tuesday that I found on Monday. :-( It's usually there somewhere in the 47,545 hits. But I've learned it's a real craps shoot.

author: nebulix
author_rank: Newbie
timestamp: August 17, 2020, 07:15:03 am
content: I'm wondering if anyone has had this counter apart? Mine came from China last week, and inside, they've substituted the master clock silver mica capacitors with rubbish, unmarked and mismatched ceramic caps. I'd like to add the proper silver mica caps. I've determined the two caps marked C29 and C30 are 33pf. for either side of the crystal. (Circled in violet).I have the blurry schematic (that seems to be the only one available online), but it's not quite the same as the board layout:For instance, the trimmer cap is labeled as Ct2. There's also another silver mica next to this labeled Ct1 that's not on the schematic. (circled in red.) Mine is an unmarked ceramic cap that I measure at 38pf. I'm wondering if this is in fact, also a 33pf cap. If someone can tell me the value of that capacitor, it would be greatly appreciated, as I'd like to replace it with a silver mica.As you can see on my counter, someone has clipped one of the leads. It came this way. The vendor replied that I could just "weld" it back on. (Well, I don't own an oxy-aceteline torch, so I soldered it instead!) Such shoddy work, just to cut corners to save on silver micas (which have become fairly expensive of late.)Rather than send it back, I'd like to repair it. On a Russian site, they show the inside of the crystal oscillator (below). It seems to be a regular HC-51 sized crystal laid flat on the board. It appears that they bend over a transitor from the regulator circuit to use as an "oven" to warm the crystal, and it's all gooped up with thermal compound. There also appears to be a resistor or thermistor in there as well. The two crystal leads go straight to the AT89C4051 microcontroller.I'm wondering if this whole thing could be replaced with a proper crystal oven, (someone mentioned having done this on another forum) or whether the current transistor "oven" is good enough.Any thoughts on this would be welcome.