53 year old electronics - Page 1
Forum section: electronics / projects

author: WZOLL
author_rank: Regular Contributor
timestamp: April 19, 2015, 03:02:28 am
content: I know this may not be the place for this but I want everyone's opinion. I have a Civil Defense Lionel (yes the model train company) cdv-700 model 6b Geiger counter made in 1962. I'm trying to keep it original but I'm thinking about reworking the board and replacing the electrolytics, resistors, voltage regulator, etc. I'm afraid that after 53 years the voltage regulator and other electronics have failed putting my $170 Geiger tube at risk. The radium in the regulator has a 98% chance of being decayed and overvolting the tube and the electrolytics are also most likely dried out. I'm also concerned about the accuracy. There is a parts kit on ebay for ~$22 on ebay but i would still like to keep the original parts to say that it still works after 53 years. i also need some tips on how to desolder the parts without lifting the copper traces off the board. I can post some pictures if anyone wants to see.

author: jh15
author_rank: Frequent Contributor
timestamp: April 19, 2015, 03:12:57 am
content: I never heard of a radium regulator, can you explain?Old PCB's need good rework techniques to prevent damage. I would think a hakko 808 or good solder wick and a good iron.

author: WZOLL
author_rank: Regular Contributor
timestamp: April 19, 2015, 03:19:15 am
content: Some older regulators contain radioactive substances and gasses to do the regulation (to be honest i don't exactly know how they work) and usually the glass blocks all the radiation.

author: bills
author_rank: Frequent Contributor
timestamp: April 19, 2015, 03:44:08 am
content: Quote from: WZOLL on April 19, 2015, 03:02:28 amthe resistors are likely to be ok, for the caps just clip them off near the body of the cap and solder the new ones on the old leads. Post some photos I have a couple old CD Geiger counters but they are tube/valve type.

author: pickle9000
author_rank: Super Contributor
timestamp: April 19, 2015, 03:55:13 am
content: Applying fresh solder will make the old stuff easier to remove. Use a fairly large tip on your iron. If the board is coated/varnished knock or scape it off. Old solder can become porous, if you clean it with anything (iso for example) you will have a difficult time heating up the joint and a pretty good bit of spatter may occur as well. To remedy that just allow to air dry a day or so. A Soldapullt works well for stuff like this.

author: bills
author_rank: Frequent Contributor
timestamp: April 19, 2015, 04:11:35 am
content: old circuit boards don't do well with heat, best to cut off components and solder to the old leads.

author: Teledog
author_rank: Regular Contributor
timestamp: April 19, 2015, 05:06:07 am
content: Have a bunch of old CDV-700s.Only mods I've done (and rarely) were for experimental probes/changing the HV tube/diodes..perhaps a cap or 2, ...if it ain't broke...don't fix it!!!A: open it it & smell it/check it..never leave the old D cells in it for longer than necessaryif it's vinegary smelling, definitely check the caps - keep the original (or more) desiccant bags in itB: the uranium test spot is probably OK..if you can find an old orange Fiestaware dish/bowl/coffee cup in a junk shop, it WILL bury the needle! Really!There's TONS of websites out there on the CDV-700 (and Yahoo groups)G' Luck! (and don't get rid of that sucker!..or fudge it unnecessarily ..read, read read..)

author: DavidJRobertson
author_rank: Regular Contributor
timestamp: April 19, 2015, 05:25:48 am
content: Radioactive regulator?I'd imagine it has a check source but that just seems bizarre. Anyway if it is radium the longest-living isotope has a half life of 1600 years so should still be plenty left

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 19, 2015, 07:07:06 am
content: Oh, you must mean a gas discharge shunt regulator? If they contain radioactive material, it's usually something like nickel (which does decay relatively quickly; radium itself takes millenia to decay), which serves to reduce the ignition voltage. The arc voltage is more or less unaffected. If it is glowing (and at the correct color, if you're familiar with the characteristic color of that type of tube), it's fine.Tim

author: SeanB
author_rank: Super Contributor
timestamp: April 19, 2015, 09:39:55 am
content: With the resistors you will find the carbon composition ones which are over about 47k are almost always going to drift high in value. how much they drift, and if it is a problem is going to depend on the function of the resistor.

author: WZOLL
author_rank: Regular Contributor
timestamp: April 19, 2015, 06:38:16 pm
content: Thanks for the feedback. There is also a selenium rectifier which may be damaged. It smells a little funny inside but I think I'm just going to replace the regulator with some zeners and also replace the rectifier.The pictures file sizes are too large. sorry. I could probably also put the new regulator and rectifier in parallel with the existing parts so i can keep it original.