I will try this confirm what i saw when the relay wouldn´t close properly changing programs, i looked at the relay at power off and it clearly did not close until a couple of seconds after power off.
Is this something i can use for the test?
Ok, thanks. The original relay did work for 30+ years so i thought a NOS relay that is only used 2 years or less would be as new and not faulty.
Time will tell if this, the third relay will hold up better than the last.
As for dirt, my Citation 25 is clean inside and i don´t see how dirt would enter the relay behind the clear top?
If we are still around 2028 i will let you know if it´s working or not🙂
Again thanks to both you and Mooly, Kent
Open relays statistically fail way more often due to moist, dust, mold, particles in air etc. Not always visible but a sealed relay simply can’t have debri creeping in. What can’t come in can’t cause trouble.
This relay has a mechanical delay. Can be due to remanent magnetism, fatigue of mechanical parts or spring, dirt/age hardened fat in the mechanism, sticky contacts etc. You say seconds and then it is noticable which is unusual. Often it can be difficult to notice. Guilt by association works quite good in electronics hence the questions. A parts reputation also helps profiling errors. An earlier replacement being a dead giveaway, using the same notorious (and also aging) type again a mistake.
This relay has a mechanical delay. Can be due to remanent magnetism, fatigue of mechanical parts or spring, dirt/age hardened fat in the mechanism, sticky contacts etc. You say seconds and then it is noticable which is unusual. Often it can be difficult to notice. Guilt by association works quite good in electronics hence the questions. A parts reputation also helps profiling errors. An earlier replacement being a dead giveaway, using the same notorious (and also aging) type again a mistake.
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That looks OK. Has that LED already got a built in resistor? but it doesn't matter and adding another is fine.
New problems. Now that the preamp has a working relay, the program selector has started to struggle. When playing the radio and CD, it sounded from both at the same time regardless of program selection. Took the unit apart and discovered a leaking capacitor at one of the LEDs by the phono function button. I changed it and took the opportunity to change the capacitor also for the other LEDs on PCB 4 which is the program selector board. Now everything worked as intended, except that the LEDs glowed dimmer than normal. After listening for a while, i switched off. When i later switched on, a buzzing sound was heard for a few seconds, but the unit still worked. A little later, all the LEDs at the program selector went out. According to the schematic it should be 18.4 volts to PCB 4, but when measuring I only see about 4 volts. What could have gone wrong? I have -19.1 volts at pin 9 of IC 756 but only around 4 volts at Q861 to PCB 4.
See what you have at the +19 volt regulator. Check the 4.7 ohm hasn't gone open circuit. Check the input to the reg (on the emitter) is around +34 volts.
At the arrow we have 32,1 volts. The other two legs of Q95 measures 5,3 volts. The R101 measures 5,1 Ohms. After the R101 i measure 4,6 volts. Seems like Q95 is faulty?
I guess i could replace the 2SK246 with a 2SK364 for a test? I will turn the 364 180° of course.
Just looking closer at that circuit and it looks like there are some errors... D91 and C97 are the wrong way around 😱
What voltage do you have across R101. Very important to see if it is in current limiting mode.
What voltage do you have across R101. Very important to see if it is in current limiting mode.
Just posted quickly above as I saw you were around 🙂
I would doubt the FET is faulty. If we have 0.5 (ish) or more volts across R101 then Q97 turns on and limits current flow which in turn means the voltage is limited. 4.7 ohms would allow around 100 to 120 milliamps to pass before entering limiting.
First suspicion has to be a fault elsewhere on the rail and quite possibly no problem with the regulator.
If Q91 is hot its passing lots of current and that is a good guide that the output has limited.
The FET is just an easy way to get a constant current source to supply the Zener. I really doubt any problem with the FET but you can just fit a resistor in place of it to test. We are there yet 🙂 it won't be faulty.
I would doubt the FET is faulty. If we have 0.5 (ish) or more volts across R101 then Q97 turns on and limits current flow which in turn means the voltage is limited. 4.7 ohms would allow around 100 to 120 milliamps to pass before entering limiting.
First suspicion has to be a fault elsewhere on the rail and quite possibly no problem with the regulator.
If Q91 is hot its passing lots of current and that is a good guide that the output has limited.
The FET is just an easy way to get a constant current source to supply the Zener. I really doubt any problem with the FET but you can just fit a resistor in place of it to test. We are there yet 🙂 it won't be faulty.
Seems you will have a strong opinion in the future on 30 year old caps and their (in time) replacement 🙂 Rücksichtslos, all of them.
Maximum thread time limit reached so good luck with the repair!
Maximum thread time limit reached so good luck with the repair!
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Q91 gets really hot, can barely touch the heat sink. The Q688 behind the sink are also hot darkening colour on board.
With the 364 in place for Q95 the led indicators has lighten up, although somewhat dim. At Q95 i now have 31,7 volts in and 6,7 volt out.
Can i use any resistor, like the one on my previos picture, to replace Q95 for test?
Can i use any resistor, like the one on my previos picture, to replace Q95 for test?
Its not the FET, something else is going on. I think you will find something on the 19 volt line is zapped and putting the regulator into current limit. There is no easy way to go about this and one thing I'm struggling with piecing all the circuit together from an online manual, its not like having a pull out paper manual where its all on one sheet 🙂
So back to the 19 volts.
One thing you could do is see if one of those LC1818 chips is getting warm. The 19 volt feeds those.
It would also be logical to look in the area where this failed cap was. Which one was it?
So back to the 19 volts.
One thing you could do is see if one of those LC1818 chips is getting warm. The 19 volt feeds those.
It would also be logical to look in the area where this failed cap was. Which one was it?
The failed cap on PCB 4 was C773. I also replaced the C774, C775 and C776.
Since the last post i replaced the 2sk364 (Q95) with a resistor for testing and found 0 volts at both ends and for a moment i noticed some smoke from the board? Anyway i regretted that i even mounted the resistor, just didn´t feel right, so i thought it would be a good idea to put the 2SK246 back for testing and measured 32 volt in and 0 out so it was removed and i put the 2SK364 back again as the function buttons and led did work somewhat with this. I also replaced the C97. Now i measured 34 volts in but 0 volts out at the Q95 so i went on and checked voltage at Q91 when suddenly R97 went up in smoke. So now i´ll have to order some 100 Ohm 1/2 W carbon resistor before further investigations. Also, i will order a suitable replacement for the 2SK246 if i can find one.
Since the last post i replaced the 2sk364 (Q95) with a resistor for testing and found 0 volts at both ends and for a moment i noticed some smoke from the board? Anyway i regretted that i even mounted the resistor, just didn´t feel right, so i thought it would be a good idea to put the 2SK246 back for testing and measured 32 volt in and 0 out so it was removed and i put the 2SK364 back again as the function buttons and led did work somewhat with this. I also replaced the C97. Now i measured 34 volts in but 0 volts out at the Q95 so i went on and checked voltage at Q91 when suddenly R97 went up in smoke. So now i´ll have to order some 100 Ohm 1/2 W carbon resistor before further investigations. Also, i will order a suitable replacement for the 2SK246 if i can find one.
This is the 12 volt reg and this uses a resistor as you can see. The FET just offers very very slightly better performance and stability.
The Zener in each reg runs at around 5 milliamps so your replacement resistor should be (34-20)/0.005 which is 2800 ohms. We would use a 2700 ohm here although a 2200 or 3300 would also be OK.
If you have used something very low you have likely fried the Zener.
Q97 may also have suffered.
If this is what happened (to a low a resistor value used) then these are all minor things that can be put right in minutes but you are still left with the problem of something pulling to much current on the 19 volt supply. Q97 can be any small signal type rated at 50 volts or more and 100ma current or more such as a BC546.
If you look at the circuit the LED is connected via a series 1k8 resistor which means even if the cap went short it could do no harm. The LED wouldn't light but that is all that would happen. If it has leaked corrosive gunge onto other leads and parts then that can cause issues.
The Zener in each reg runs at around 5 milliamps so your replacement resistor should be (34-20)/0.005 which is 2800 ohms. We would use a 2700 ohm here although a 2200 or 3300 would also be OK.
If you have used something very low you have likely fried the Zener.
This would also happen if you used a low value resistor in place of the FET. The resistor is trying to supply all the current into the 19 volt rail under a fault condition rather than pulling the voltage of the regulator down to safe limits.
Q97 may also have suffered.
If this is what happened (to a low a resistor value used) then these are all minor things that can be put right in minutes but you are still left with the problem of something pulling to much current on the 19 volt supply. Q97 can be any small signal type rated at 50 volts or more and 100ma current or more such as a BC546.
So this one:
If you look at the circuit the LED is connected via a series 1k8 resistor which means even if the cap went short it could do no harm. The LED wouldn't light but that is all that would happen. If it has leaked corrosive gunge onto other leads and parts then that can cause issues.