GE Clock - Phone Radio 7-4737A - no radio on wake to music - Page 1
Forum section: electronics / beginners

author: allen305
author_rank: Newbie
timestamp: April 16, 2020, 03:17:21 am
content: I have a GE Clock - Phone Radio 7-4737A and complete schematic. When the Wake on Music (radio on) is set, there is no radio, just noise. The radio works when turned on. When Wake on Alarm is set, the alarm sounds. Volume controls alarm, and noise. The radio has 2 ICs: one for radio & amp; and a second for clock / alarm. I have tested diodes, resistors, and capacitors in the Wake circuits, but I have found no faulty components. Quite frankly, I am lost at where the failure may be. I do not see any burnt or blown components. I originally suspected a capacitor was shorted to ground, but I have not found any. There is a switch (NPN transistor) labeled "CR" which has a pinout from the clock IC, but I do not know what "CR" is. The "CR" circuit seem to be a control for the Wake functions.I'm sure a repair shop could fix this device, but I would like to fix this clock radio. I can post the schematic if that would be a help. Any suggestions would be appreciated. Thanks :-).

author: floobydust
author_rank: Super Contributor
timestamp: April 17, 2020, 05:01:32 am
content: Welcome to the forumsThe only difference between manually switching on the radio and the clock chip doing it, is a transistor switch. CR means clock radio.The radio might run off say 9V power but the clock chip circuit only provides say 4V, so the radio is weakly on. This is the only way I can make sense of your symptoms. So I'm saying the transistor is low beta/damaged, they do get hot if the radio is cranked up.Have to see the schematic, or follow the ALARM OUT to a transistor and measure the radio's power supply voltage with manual switch on compared to sleep to music/wake to music driving the radio.

author: greenpossum
author_rank: Frequent Contributor
timestamp: April 17, 2020, 05:20:01 am
content: Yeah post the schematics as floobydust said and then we might be able to suggest points in the circuit to take measurements. Hopefully it's as simple as a failed transistor.

author: allen305
author_rank: Newbie
timestamp: April 17, 2020, 06:54:03 am
content: Thanks for the replies. I have added the GE Clock Radio Schematic in first post. I appreciate any suggestions. Thanks :-).

author: floobydust
author_rank: Super Contributor
timestamp: April 17, 2020, 07:30:06 pm
content: The schematics really help, I'm going with my wild guess the transistor is lazy.Transistor Q3 TUNER SWITCH switches the radio power on by connecting its ground - awkward but anyhow the radio should be getting steady ~11VDC when (Q3) on. This comes from the power supply D1, C52. Q3 gets turned on by clock IC alarm out or sleep out or function switch on. Q3 gets less base drive from the IC compared to the function switch radio on which might explain the difference. Measure the radio's voltage on compared to sleep/alarm on, across C53 or something.The clock IC seems to always output a beep-beep-beep at the ALARM OUT- but the radio would like steady power. So there might be a design weakness if missing a filter. C53 100uF would cover that a little.The power supply is complicated because it has four loads (VFD filament, VFD brightness, clock IC, radio) and circuit common is not ground for the radioGiven the age, I had to replace electrolytic capacitors in the power supply on my old Randix cube clock radio, so I would suspect them and Q3 being lazy or R47 burnt.I think the main clock IC2 is a LM8560 and so the CR INPUT is:"When the AC power supply is interrupted, the time-counter switches to a holding state and a built-in oscillator promptly begins operation. If 50/60Hz input (loss) continues for 3 clocks without arriving, this oscillator’s output is activated and functions as the time-counter clock in place of 50/60Hz input. The frequency level of this clock oscillator is determined according to the CR value. While the above mentioned oscillator is operating using backup mode, all segment outputs are switched to OFF."So if there is a power failure, the CR SWITCH Q4 goes off and the clock IC uses it's internal oscillator for timekeeping, running off the battery, and blanking the display. I'm not sure if the alarm still works on battery power though.

author: allen305
author_rank: Newbie
timestamp: April 18, 2020, 01:03:00 am
content: Thanks for the great analysis :-). Thanks to you some of the circuits make more sense. I did test Q3 and Q4 with a transistor, capacitor, diode, and resistor tester. They tested okay. I have tested many of the capacitors around the CR and Tuner switches. I have not tested the resistors. I will let you know what I found. Also, I replaced the above schematic pages with high resolution scans. Best wishes!

author: allen305
author_rank: Newbie
timestamp: April 18, 2020, 03:55:18 am
content: The Q3,Q4, and Q5 transistors are BJT-NPN 6002-012 (ECB left to right). I have not found a datasheet for these transistors. Here is the test information: Q3 hFE 143; Vf 871 mV; Q4 hFE 122 Vf669 mV; Q5 hFE 122 Vf 674 mV. Resistors R47 and R48 tested within the 5% tolerance (Gold). I have not tested the voltage on Tuner Switch. That will be next. Oh, I burnt the dial tuning cord. Is there a special cord for replacement? The repair manual shows the way to re-string the cord if i can figure it out. :-(.

author: allen305
author_rank: Newbie
timestamp: April 24, 2020, 02:41:03 am
content: Most of the transistors are labeled 6002-012 npn. I cannot find a datasheet for this transistor. Is there a present day equivalent npn transistor? Q3 in the GE clock radio has a hFE and Vf higher than Q4 and Q5. How do I test the voltage on radio Alarm than radio "On"?

author: floobydust
author_rank: Super Contributor
timestamp: April 26, 2020, 12:12:44 am
content: That looks like a GE house number for the transistor, are there any other digits? What package is it in. I could find nothing for datasheets on it.I don't like Q3 having a higher VBE compared to the others and would replace it or at the very least try swap it for another. ECB is typically Japanese JEITA pinout.The transistor Q3 gets base drive ~15mA from the function switch or ~5mA from the clock IC. Assuming the radio uses ~100mA (sometime more if there are dial lights or it's cranked loud), you would like beta to be 20-200 and 200 is better for saturation.Usually these radio-switch parts are TO-92+ or TO-126/TO-225AA package for medium power, I would put in a 2SD882Y orKSD882YorBD135, these are beefier parts.A small plastic TO-92 likeBC337-25would work and bend the pins (CBE) to match (ECB). A jellybean transistor i.e.2N2222whatever you have lying around could work but EBC pinout and it would heat up a bit if the beta is low.

author: allen305
author_rank: Newbie
timestamp: April 26, 2020, 04:31:25 am
content: Thanks for the reply. The transistors also have a T 626 printed under the 6002-012 number. They are all TO92 package, but the base is the 3rd pin. I swamped Q3 for Q7 (light dimmer switch) to no avail. Q7 did have the same hFE and Vf as the others. Where should I place the VOM meter leads to check C53? Where do I test the voltage on radio Alarm than radio "On"? It looks like radio "On" connects to the Vs pin (negative) on the IC.Another weird thing, when the radio is switched to FM and the Wake on Music is "On"; the alarm noise (beeping) can be heard. But when set to AM and Wake on Music, you hear a static pulsing noise. I checked C39 and D9, but they test okay.I maybe over my head on this one. I just don't want to give up. I'm old and so is the radio, but I'm still working.

author: floobydust
author_rank: Super Contributor
timestamp: April 26, 2020, 07:17:05 pm
content: Is the clock IC the original one? any part number on it? My wild guess is an LM8560.The problem as I see it is the radio is not getting smooth, clean power when the clock IC turns on Q3, which it does for Sleep to Music or Alarm. There is a possible design bug in that the clock IC alarm output only beeps when it activates. So the radio would get "beeps" on its power with the alarm on, which is what you are hearing. Sleep to Music or function switch-on, the radio would work fine.I would measure the radio's power supply voltage when it's on due to Alarm On compared to the function switch or Sleep to Music. There's three different ways the radio gets activated. The radio gets power OK with the function switch to Radio On? which also turns on Q3 minus the alarm beeps. Measure voltage across C53 and see if it stays around 11V. Originally I thought transistor Q3 was lazy but we must have some other problem. I would also remove and test C53.To fix the design bug, add a capacitor 10uF 16V, (+) to pin 17 on the IC, (-) to COMMON (just like C39 on pin 16) or another location could be from R47/R48 junction to COMMON. This added capacitor filters out the alarm beeps.You can figure this out, always an adventure fixing these.