WE #20B2 P/S Failure

[Babybearjs]

well, it happened again.... well, sort of.... on my #20B2 Power supply I lost BOTH of my batteries ("A" and "B") the 10 and 18 VAC are working OK, but I had to pull out my 101G P/S as backup. does anyone know what I should look for? I'm wondering if A capacitor has gone out.... I was think about using the parts from the 101 to repair to #20B2, but decided not to.... If I can find an electrical shop that can repair it, I'll send it there.... if not, I'll be looking for another #20B2. the 101G is OK, but I had to repair it once and have 5 wires coming out of the bottom of the unit being terminated on a barrier strip. looks tacky, but still works... I also found out that on both power supplies, the ground is common.... so all my ground wires are too....  so, if anyone has another #20B2 power supply they don't want anymore.....I am looking....

[Dave F]

If both the A and B DC voltages are bad it sounds like either the rectifier has bitten the dust, or possibly a transformer winding has failed.  A bad capacitor would blow fuses if it was shorted and just cause AC hum on the DC output if it was open.  A bad rectifier can be replaced, but if it is the transformer you are looking at a new power supply.

DF

[Babybearjs]

Thanks.... I'm going to call a service center here in Boise to have it diagnosed...

[Victor Laszlo]

There is no need to "call a service center" whatever that means.  Are there really places in Boise that a telephone hobbyist can take a 30-year old piece of obsolete telephone equipment and have it diagnosed and repaired?

A power supply is a very simple device. I have fixed many. All you need is hand tools and a soldering iron.

Take your voltmeter and do a little probing. Loosen the faceplate and find the bridge rectifier. It is a black bakelite or plastic square, approx 1.5" x 1.5" by 0.5" in size. It has 4 terminals. 2 of the terminals are the A-C input and 2 of the terminals are the D-C output.  The inputs are marked with  ~  (looks like a sine wave) which stands for "alternating current"  The outputs are marked with  + and  -.

See if there is 18Vac going to the input terminals of the rectifier. If yes, then check the output terminals of the rectifier for 24Vdc.  If there is no A-C voltage going to the inputs, then you have two choices. Replace the entire power unit, or swap the inputs on the rectifier with the existing, assumed working, 18Vac wires that feed the 18Vac terminals on the front of the unit.

If there is no 24Vdc at the + and - terminals, of the rectifier, either make a new one from 4 diodes (cost approx $0.40) or buy one at Radio Shack or on Ebay for a few bucks, and replace the defective one.

[unbeldi]

What exactly led to the demise of the supply?
With most collectors' use of key systems, the supplies run mostly idle drawing very little current.  Rectifiers typically don't burn out during times of little use, rather they fail under loading conditions, or when unprotected from power surges.

Did you by any chance short the output accidentally ?
Have you already checked the fuses ?

The transformer failing would be almost astonishing. I would follow Victor's suggestions and test the rectifiers.

Even if you find a repair shop, it is hard to conceive that professional repair would be cheaper than finding another supply on eBay, where they typically run ca. $20 - $30, by my observations.

[Babybearjs]

Thanks for the info... I was going to see if an electrical repair shop could take a look at it.... I'll check the rectifier and the fuses again to see if I missed something... as for the fuses... I'll double check that part.  I was cleaning up my wiring and had disconnected my power ties between the KTU and the Power source. I went to re establish power when I lost my control and talk circuits... they are working fine with my 101G unit. so, I know my wiring is OK.... (update:10/22): I pulled out my unit and removed the bridge rectifier. tested the 24 volt line, got power. so the rectifier went.... reading the BSP, this was a regular issue, as they state that if a short occurs, it can blow the rectifier. so, I checked the rectifier, and sure enough... it was bad.... problem solved... what specs do I need to know about the replacement rectifier... R/S, here we come again! (Radio Shack).

[Babybearjs]

well, I finally went to Radio Shack and got the rectifier. it fixed the problem, but now..... the caps went... I started up the unit after replacing the rectifier and everything seemed to be OK when I heard some Sizzling coming from the unit.... I unplugged it. tried to see where it was coming from and plugged the unit back in.... started to sizzle again and smoke.... Yikes! pulled the power and yanked the unit.... upon inspection I found the filter caps too hot to touch... and oil.... looks like something is leaking.... would it be worth updated the caps to new ones, or just scrap the unit.... because of the age, fire is a concern.... wouldn't want to thing to light up and set the house ablaze! does anyone know what NEW replacement is out there for this vintage power supply.... I can go back to the 101G series P/S's but the aging parts is a concern......

[Stan S]

John
Are you absolutely sure you installed the diode bridge properly?
Sounds like you may have reversed the output polarity of the bridge. Electrolytic capacitors 'complain' when you do that.
Stan S.

[Babybearjs]

Wonderful! I'll have to reverse the rectifier and see.... since it was smoking and there was oil present.... I think I fried the caps.... can they be replaced with new ones? for the amount of time I've spent messing with this, I am just going to buy another 101G from Mary at Phoneco. what New replacements are available for these? is Lorain still in business? what is used today with the 1A2 systems? the voltages are still the same.... if I have to, I can get a 24 VDC P/S and a 12 VAC P/S to replace the whole system.... what do you all think?

[Victor Laszlo]

I think you need to continue the quest to learn how to repair these things, but to exercise a bit more caution and science. Get the original working properly for the satisfaction of it.

If the rectifier was installed by you in reverse polarity, you will probably need to replace the capacitor. It is a common enough type: electrolytic (which you now know implies polarity-sensitive) peak voltage 40-50, around 1000 uF to 1200 uF should be fine. Check the BSP to get the exact ratings, if you are reading an earlier BSP, before they simplified them. Does the cap have its ratings printed right on it?  For a few bucks, you can get it working fine again. No need to buy another 40-year old questionable one.

To answer your question about what do 1A2 systems use these days...hmmm...the only people using them are weird hobbyists like us and a few hardened government installations that worry about an EMP.

[Babybearjs]

what I'll do is correct the rectifier and see is it works. the caps were leaking oil but I'm hoping I caught it in time. the larger of the 2 caps was too hot to touch when I unplugged the unit.... would that indicate a failure?  I can get newer power supply parts through all electronics... uninterruptable power supplies (like what the computers use, but only in a 24 volt version....) I know newer stuff is out there, I just have to look.....

[unbeldi]

what I'll do is correct the rectifier and see is it works. the caps were leaking oil but I'm hoping I caught it in time. the larger of the 2 caps was too hot to touch when I unplugged the unit.... would that indicate a failure?  I can get newer power supply parts through all electronics... uninterruptable power supplies (like what the computers use, but only in a 24 volt version....) I know newer stuff is out there, I just have to look.....

No matter what you do, make sure you wear eye protection, just in case the capacitors explode.
But, I would not power up the supply again without replacing the elcos, unless you test them with a capacitance meter. The electrolyte is likely destroyed when it gets that hot. If the the capacitor is shorted you're likely to destroy the rectifier too.

These are powerful supplies and you must make sure that everything is connected properly before powering up.  If you have any uncertainty about that, then don't do it yourself.

[Babybearjs]

Thanks for the warning. I'll most likely be upgrading. I'm using my old 101G right now, and its working OK. the VOIP modem won't support more then 1 ringer, so I only have the bell on in the Kitchen. I'm so tired of trying to get these things to work, along with safety issues... the newer, the better.... these old P/S's  are really nice, but because they are over 30 years old.... the transformers are worn out and become a fire hazard. the paper wrapping on the transformers are sooo dried out.... it scares me...and the windings are showing....etc. Using a new Power supply seems to be the best thing to do... the pictures posted are just some examples of whats available....