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Heathkit Super Clock GC-1195 w/chimes

Discussion in 'Troubleshooting and Repair' started by iluvtubes, Jul 30, 2007.

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  1. iluvtubes

    iluvtubes

    1
    0
    Jul 28, 2007
    Hi,

    I'm a newbie on this forum and I was hoping someone can help me with a power supply problem in a Heathkit Super Clock GC-1195 w/chimes.

    I built this clock in 1976 or thereabouts and has been very reliable. I had to replace D101 & 102 (which are 2 diodes in the bridge) in 1987 for an intermittent condition. The original diodes had a forward current rating of 2A and a PRV of 1000V. I replaced them with ECG 5802 which has a forward current of 3A but only a PRV of 200V. I didn’t think that the lower PRV would be a problem because it’s only an 18v power supply. I guess I was correct in my thinking because they lasted for 20 years! Now the diodes opened up. I bought new ones today, ( 1N5404) which are rated at 3 amps and 400 PRV. I put them in and the clock works great except the diodes seem to run excessively hot! The B+ at the filter is at 18 volts just like it should be. There are some + or - 1 volt variations depending on how many bulbs are lit, but even at 1:11 O’clock with the bulbs dim, the diodes still seem to run too hot.

    This is where it gets a little heavy! In 2001 I replaced all the bulbs with E5 screw base types because the wedge base bulbs were so problematic. I replaced all the wedge sockets with screw type and used T - 1-3/4 midget screw bulbs which are rated at 6.3 volts @ .2 amps. The originals were 5V @ 120 mA T-1 Wedge. Orginals are 5V x .12A = .6 watts. The replacements are 6.3V x .2A = 1.26 Watts. I thought that was my problem, but like I said before, it can be at 1:11 & dim and the diodes still run hot.

    Anybody have any ideas?

    Thanks,

    Jim A.
     
    Last edited: Aug 1, 2007
  2. Lenp

    Lenp

    24
    0
    Sep 8, 2009
    I don't have the clock schematic on hand but it sure seems that the lamps are the issue. The diode heats because of the current through it. It may be possible to upgrade the diode current rating or to heat sink it but the power transformer and lamp driver transistors may also be overloaded.None are good for long life.
    Consider white LED'S with approporiate dropping resistors?
    Len

    .
     
  3. loumsc

    loumsc

    3
    0
    Jun 28, 2010
    Hi Jim,
    I supply and/or install an LED upgrade kit. The current requirements are much lower and there is no heat.
    Thnx,
    Lou D.
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,505
    2,849
    Jan 21, 2010
    Another option is to leave more lead length connected to the diodes. If the PCB is not providing any heatsinking, the additional lead length may be.

    It is possible that the filter capacitors have become leaky in their old age and are consuming additional power (do they seem to get warm?)

    It sounds like something is consuming more current than it once was.

    Whilst replacing lamps with LEDs may be an option to reduce current consumption, I would try to identify what is consuming *extra* current first.

    Replacing lamps with LEDs may give you a far different "quality" of light that is not in keeping with what is probably now a very retro design :)
     
  5. loumsc

    loumsc

    3
    0
    Jun 28, 2010
    Hot Diodes

    On another note, I have upgraded and/or repaired over 100 of these clocks and they all have a heat problem with the diodes. It is so bad that several have burned the pcb to the point that it has become brittle and cracked. If you noticed that the installation of (2) of the diodes had them installed with a 1/8 to 1/4" gap from the board because of the overheating problem.

    Lou D.
     
  6. loumsc

    loumsc

    3
    0
    Jun 28, 2010
    GC1195

    On another note, I have upgraded and/or repaired over 100 of these clocks and they all have a heat problem with the diodes. It is so bad that several have burned the pcb to the point that it has become brittle and cracked. If you noticed that the installation of (2) of the diodes had them installed with a 1/8 to 1/4" gap from the board because of the overheating problem.

    Lou D.
     
  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,505
    2,849
    Jan 21, 2010
    Sounds like a design problem to me. 2A through a suitable diode shouldn't result in so much heat. Is it a fibreglass board, or one of the cheaper and less resilient alternatives?

    Perhaps the peak current is much higher than 2A -- a definite possibility if it's a simple bridge rectifier charging a large filter capacitor.

    Simple fix... not sure. I can think of one (a large choke) but I imagine there will not be room for that.
     
  8. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    I downloaded the diagram and the psu is based on an 18V CT transformer rectified in a bridge configuration, resulting in 18V DC on a 1200uF capacitor.
    The center tap is fed through Q1 making 5V. The two diodes running hot are feeding the negative side, so they are handling the sum of both the 18V & the 5V currents.
    My initial urge is to replace them with Schottky types. They can handle twice the current in the same size as 1N5401's due to their much lower forward voltage drop.
    But be sure to pick ones that have a high voltage rating, combined with a low forward voltage drop.
    Their reverse leakage current can get very high when exposed to high voltage and high temperatures and can contribute significantly to the total heat generated in them.
     
  9. whitetm

    whitetm

    12
    0
    Feb 15, 2021
    Lou,
    How did the led kit work? I haven't been able to find a kit for my clock. What size resistor used to drop the 5 volts down to I guess about 3-3.5 volts for the led?
    Tom
     
  10. Bluejets

    Bluejets

    5,529
    1,163
    Oct 5, 2014
    Think you could poke it in here for us to see as well...??
     
  11. Martaine2005

    Martaine2005

    3,999
    1,086
    May 12, 2015
    Resqueline was last seen in 2012.
    Just saying..

    Martin
     
  12. Martaine2005

    Martaine2005

    3,999
    1,086
    May 12, 2015
    @whitetm
    What LED do you want to use?

    Martin
     
  13. Bluejets

    Bluejets

    5,529
    1,163
    Oct 5, 2014
    Yeah, sucked in again.
    Think they could mark these in some way, don't always look at the date.
    Will in future though.
     
    Martaine2005 likes this.
  14. whitetm

    whitetm

    12
    0
    Feb 15, 2021
    Hi Lou,
    Did you find a way to get the colon led to flash on the heath-kit gc1195/gc1197 clock as well? Oh, I did find warm white led's for the clock
     
  15. whitetm

    whitetm

    12
    0
    Feb 15, 2021
    I did find some warm white leds that run on 3.4 volts @ 24ma
     
  16. bertus

    bertus Moderator

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    Nov 8, 2019
  17. Martaine2005

    Martaine2005

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    May 12, 2015
    If it’s 5V supply and 3.4V Vf, you only need to drop 1.6V.
    For 24mA a 66Ω resistor. 20mA an 80Ω resistor.
    But you wouldn’t really want to go lower than a 100Ω.
    You might find it’s too bright and only want 8 or 10mA. So 160Ω or higher.

    Martin
     
  18. whitetm

    whitetm

    12
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    Feb 15, 2021
  19. whitetm

    whitetm

    12
    0
    Feb 15, 2021
    Thank you Martaine. any idea how to get the colon to flash dim to bright with a led? The Incandescent lamp does flash from dim to bright
     
  20. Martaine2005

    Martaine2005

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    1,086
    May 12, 2015
    What are the voltages when it’s bright and dim?

    Martin
     
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