Can anyone help with a hot transformer?

[martin martin]

I found this in storage and thought it would clean it up. I built it about that time...

It's a an 1982 vintage  HEATHKIT GC-1092D 

I replaced all of the electrolytic caps.  It keeps fine time, except the power transformer is running at 195 F

Any ideas?

thanks in advance!

[Adrian Pardini]

Try running it outside the clock and see if still over heats.
If it doesn't look at the rectifiers.

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Adrián Pardini

[alb.001 alb.001]

I bought two different models of Heath Kit clocks with flat planar neon displays.    They were both plugged into two outlets on the same AC extension cord and then the extension cord was plugged into a wall receptacle.   One runs as 24 hour clock, other one is a 12 hour clock   After a few days they are not at the same time  and the longer they run the further apart they get.  I thought that they both used AC line frequency for timekeeping.    Any ideas,  I'm stumped by this.

Thanks  Phil B.

ts---------- Original Message ----------
From: Adrian Pardini <pardo...@gmail.com>
Date: November 16, 2019 at 8:56 PM

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[jf...@my-deja.com]

Do they both run fast?  Designs that simply count the mains are susceptible to noise pulses adding to the total, and most early designs were prone to this defect. If this is the case, I would try filtering out the noise spikes: ferrites on the primary side, and a low-pass on the rectified line frequency reference.  (One exception was the CT-700x which could be made to run  little slow or fast, depending on the setting of the MUX rate.)

[alb.001 alb.001]

one runs correctly, the 24 hour version runs fast

thanks for the insights

Phil B.

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[Jeff Walton]

One solution for filtering noise on the mains to your counter input is to set up a one-shot input that has a time period equal to just a little less than 60Hz (or 50Hz).  That way, the counter input will not see anything between the cycles.  I did this on some TTL clocks back in the 70’s and it was a perfect solution.  For 60 Hz, a value of 14-15ms for the one shot period should be effective.  I used a 74121 for the TTL version of the circuit.  Probably lots of other ways to do it.  The point is that you only want your counter to accept an input change once during a defined period, as anything else would be noise.

 

Jeff

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[martin martin]

The clock I posted keeps perfect time.  Just the transformer runs way to hot.  I haven’t changed all the rectifier diodes yet though

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mcve...@gmail.com

[gregebert]

Is anything besides the transformer getting warm ? This is where a laser thermometer is very handy.

How dirty/dusty were the PC boards ? In my garage it's possible for metal fragments to get everywhere.

Try brushing/vacuuming/blowing w/ compressed air. I know it sounds gross, but sniff around for cat pee.

I've had several things sprayed.

Any chance you are running at 240V ? If the transformer is set for 120VAC that will cause overheating.

I've never had a traditional power transformer fail on me unless something happened to it (water damage, overloaded)

I suppose it's possible for the laminations to develop a short/leak. Only way to find out is to remove the transformer and bench-test it out-of-circuit.

[Dekatron42]

Did you replace all of the small green tantalum capacitors too? I've had a few that acted as shorts more or less and some that went up in smoke.

Did you place all of the electrolytics with the right polarity? Swapping plus and minus sometimes will result in excessive current draw if they cook and dry up shorting internally.

Checking the current draw on all voltages will probably give you a good idea on if you are drawing too much from the transformer and on which winding.

/Martin

[martin martin]

Using an IR thermometer is shows 195F  after 3 minutes.  I was about to find this schematic - I did not make the markings.  There's no regulator, just Zeners

[Adrian Pardini]

On Mon, 18 Nov 2019 at 21:34, martin martin <mcve...@gmail.com> wrote:
>
>
> Using an IR thermometer is shows 195F after 3 minutes. I was about to find this schematic - I did not make the markings. There's no regulator, just Zeners
>

That's a bit hot but not that much (around 90°C). On the schematic
that you posted I see the nominal voltages, are those more or less the
same on your clock? How about R201?




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Adrián Pardini