About 20° C.
I also have a feeling that the relay stops working when the unit gets warmed up.
Hence my original question, which component affects the function of the relay when the unit is warm.🙂
I also have a feeling that the relay stops working when the unit gets warmed up.
Hence my original question, which component affects the function of the relay when the unit is warm.🙂
Transistors, diodes, ICs, caps and (not that usual) resistors. Solder joints too, hence the freeze spray fault finding. About all parts really but highest suspects electrolytic caps and transistors that have become warm regularly 🙂
Won't read back but with old stuff all solder joints must be reworked anyway. Best is to combine that with replacement of aging sensitive stuff like electrolytic caps. Your issue is a tough one to solve just like most intermittent errors and I think I would replace the TC4069BP anyhow as it is early CMOS stuff.
Won't read back but with old stuff all solder joints must be reworked anyway. Best is to combine that with replacement of aging sensitive stuff like electrolytic caps. Your issue is a tough one to solve just like most intermittent errors and I think I would replace the TC4069BP anyhow as it is early CMOS stuff.
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Thanks. I have replaced C2, C18, C19, C15, C17, Q10, Q11 and Q13 as well as the RL1 on the board.
I have checked most if not all solder joints in the circuit to no avail.
Next step would be to check the signal to Q10?
Also, why is there 0,067 volts at pin 6 when it should be 0 volts, is it possible Q14 is leaking "backwards" thru the emitter to pin 6?
I have checked most if not all solder joints in the circuit to no avail.
Next step would be to check the signal to Q10?
Also, why is there 0,067 volts at pin 6 when it should be 0 volts, is it possible Q14 is leaking "backwards" thru the emitter to pin 6?
Something is leaky and/or temperature dependent. When I was repair guy I had such difficult issues and had even microcracks in PCB tracks not visible with the eye. Only when freeze spray was used.
Here is the schematic with replaced parts, only C2 is replaced with a 470uF/50V as per the parts list:
I power off when relay don´t work and then power on makes the relay work again, so i don´t really think it´s heat related?
D18 shows -4,85 volts at the R22 end and -29 volts at the R21 end, is this OK?
What is puzzling is the 0,067 volts at pin 6 and at emitter on Q14, this would mean the IC or Q14 is not acting up?
D18 shows -4,85 volts at the R22 end and -29 volts at the R21 end, is this OK?
What is puzzling is the 0,067 volts at pin 6 and at emitter on Q14, this would mean the IC or Q14 is not acting up?
Please consider the phenomenon (ambient) temperature dependent leakage/unreliability. This is often combined with intermittent power on/off consequences that also heat up and cool down the part. Very hard to find and afterwards the "I thought so" feeling. Leaky parts have the habit to give normal readings when you measure but play hide and seek when you don't measure 🙂 Many have experienced this with transistors in older Japanese audio devices (with a great lot of transistors) and intermittent noise trouble. Tapping, heating up, cooling and bam there you found it. More than once devices that for instance fail every 5th or 6th time they are switched on. Or the other way around 😀
It is likely just 1 part playing up. Gut feeling says either IC1 or D18. If it becomes open connection every now and then then the relay will have delayed falling off of contacts. Plus it deals with induced voltages every time at power on/off.
It is likely just 1 part playing up. Gut feeling says either IC1 or D18. If it becomes open connection every now and then then the relay will have delayed falling off of contacts. Plus it deals with induced voltages every time at power on/off.
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Many components all work together, that is why your question can not be answered easily.
Pin 6 has to go high to turn the relay off and mute the audio. Remember relays click in both 'directions', when applying power and also when removing power.
0.067 volts would be a valid logic zero. Yes 🙂 That turns the relay on which unmutes the audio. That is how the relay driver works. Do we all accept that to be true?
If the relay 'clicks' then either power has been removed or power has been applied. It could be either to give an audible click.
With pin 6 at logic low you should see voltage across the relay coil. Can you tell us what this voltage is?
One thing we have not checked and should have done is the -34 volt rail supplying the relay.
Good idea to check the -34V. Should be one of the first things to do really. An indeed the coil voltage, please set DMM range to higher voltage.
That sounds reasonable. The -34 volts should be a constant at all times. It looks like a 24 volt relay is fitted and that it draws about 18 milliamps. Coil resistance would be about 1.3k
So all good at this point as long as the -34 is a constant under all conditions 👍
As this is proving elusive to pin down I still wonder if a simple logic probe would help. Do you have any LED's? It would show short duration pulses that a DVM may miss.
Looking at the circuit the only 'inputs' to the relay drive circuit are the voltage on point 'G' (labelled Function Mute). I suspect this is the line that should change level to perform a mute when you change programs. This is where a logic probe might help. The other input is the voltage on C19
Q14 appears to 'output' a mute signal to show the unit is muted.
One other thing you can check. When the unit is cold and working correctly can you measure the voltage across C19. Measure it and record the value. When the unit goes faulty can you see if that voltage is still the same. It should be.
So all good at this point as long as the -34 is a constant under all conditions 👍
As this is proving elusive to pin down I still wonder if a simple logic probe would help. Do you have any LED's? It would show short duration pulses that a DVM may miss.
Looking at the circuit the only 'inputs' to the relay drive circuit are the voltage on point 'G' (labelled Function Mute). I suspect this is the line that should change level to perform a mute when you change programs. This is where a logic probe might help. The other input is the voltage on C19
Q14 appears to 'output' a mute signal to show the unit is muted.
One other thing you can check. When the unit is cold and working correctly can you measure the voltage across C19. Measure it and record the value. When the unit goes faulty can you see if that voltage is still the same. It should be.
Pin 6 only goes high when i force it by shorting C and E on Q10. Otherwise it´s 0,067.
I noticed that the IC1 in my unit is marked TC4069UBP but the parts list and diagram this would be TC4069BP.
Are these parts equivalents?
This is why I think a probe might help. We have to get past this uncertainty on what is going on here.
If pin 6 is at 0.067 (or zero) all the time then pin 5 would be high at all times and you would never see (or hear) the relay change state (to click). But you do hear it click. So the logic must be changing state.
The UBP refers to 'Unbuffered'
https://www.ti.com/lit/an/scha004/scha004.pdf?ts=1730115240695&ref_url=https%3A%2F%2Fwww.bing.com%2F
On super slow speed applications like this it makes no difference which is fitted.
When cold power off 0,2 V at C19. Power on and it slowly rises to 4,5 V (relay works), when relay don´t work also 4,5 V.
Yes, pin 5 is high at all times except when program is changed, the the DMM shows O.L. when the relay clicks, then it goes back to high (4,3 V).
And pin 6 is low at all times except when program is changed, the the DMM shows O.L. when the relay clicks, then it goes back to low (0,067 V).
What does a "probe" looks like and what would i show when used on pin 5 and 6?
