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Heathkit GC-1197 Help - Skipping Beat and Chimes are Way Too Low

snappyapple632

Oct 21, 2021
3
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Oct 21, 2021
Messages
3
Hello engineers and hobbyists,

Over the past few weeks, I have been making attempts at repairing a Heathkit GC-1197 with a GCA-1195-1 chime module installed. I bought it in "For Parts/Repair" condition, assuming that the burnt-out incandescent segments were the only issue. When the clock arrived in the mail, I plugged it in to discover there was no sound. The three original electrolytic capacitors on the chime board were immediate suspects, to which I promptly replaced (with 67V of the same capacity, the originals were 25V) and could now hear the chimes properly.

However, this was only the start of a battle with an electronic Hydra, as two new problems reared their ugly heads: the chime board was skipping beats at random and the chimes sounded waaay too deep, even with the pitch all the way to the max.

Here is what I've probed into thus far using the module's built-in test probe:
  • Running through the testing instructions in the manual, I find the signal from D304 and D305 is at full intensity. Per the cause chart's recommendation, I tested D304, D305, and R322 with a multimeter. They all work fine and their solder joints are good.
  • The clock signal coming from the IC305 (the time decoder) seems normal with no signs of noise that would cause the beat to skip. However, IC314 and IC315 show a pattern with random irregularities that reflect the skipping of beats heard in the chimes. I tried swapping IC314 and IC309 (both the same CD4013BE chip) which did not see any improvements.
  • All other tests in the manual passed fine with the built-in probe.

Here is a sound file detailing the chimes and the skipping beat (it skips once at 00:31 on the file): https://drive.google.com/file/d/1AGSqt1lWC72Cqysc6UjjvHkfKbiTxLpc/view?usp=sharing

And here is a digital copy of the manual that I was referencing, featuring all the parts used and instructions with troubleshooting steps: https://elektrotanya.com/heathkit_gca-1195-1_chimes_for_gc-1195-1187_clocks_sm.pdf/download.html

At this point, I am very stumped. I'm hoping I can find some other GC-1195/1197 owners here that could have an idea of what's wrong. Thank you for your help in advance!
 

adamsfour

Sep 18, 2022
1
Joined
Sep 18, 2022
Messages
1
Another question on GC-1197. My digit are now very dim. I replaced the light dependent register (LDR) and q103 transistor but no change. The LDR is rated as full brightness value and full dark value but I don’t know what they are so I am thinking I purchased the wrong LDR. Or is there another component I need to check such as one of the capacitors
 

kellys_eye

Jun 25, 2010
5,092
Joined
Jun 25, 2010
Messages
5,092
Your situation isn't helped by a lack of schematic but the notes are generated through diode mixing so they all need testing for leakage. If the issue locates 'around' a couple of IC's then replace or improve the local supply rail suppression capacitors.

As with much of vintage electronics, replacing ALL the electrolytics is good practise.
 

kellys_eye

Jun 25, 2010
5,092
Joined
Jun 25, 2010
Messages
5,092
Dim digits? Are these the ubiquitous 'filament' seven segment devices? In which case you could potentially raise the supply voltage BUT replacement of the digit itself is the preferred method.
 
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