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I have also searched for the service manual but without result.
Made some heat / cool tests today. Cooled down and it took 5 minutes before it started so I warmed up the area around the IC605 and then it starts instantaneously. Tried several times with the same result. May be the IC605 (6 volt voltage regulator) that is defective. TR615 and TR616 are also in the same area.
Sounds like progress. Missing +5 volts would certainly prevent the unit from coming on. (I thought we had measured the output of IC605 earlier) Not sure what the 'Hold' does, but I bet it also could prevent the unit from coming on. Let's measure the volt at the cathode of D604 and the collector of TR616. Do it when the unit has been turned on but is not yet working, and again after it has warmed up an is working. While we are in the area, also measure the collector of TR614.
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Heated only IC605 with soldering iron and it turns on immediately, so it must be the IC. Have already ordered NJM7806FA Positive Voltage Regulator. And many thanks for excellent technical help and mental support
Collector on D604 = 4.92 volts, collector on TR616 = 0 volts and collector on TR614 = 4.23 volts before switching on.
In working mode, collector on D604 = 4.92 volts, collector on TR616 = 0 volts and collector on TR614 = 5 volts.
Both the collector of TR616 and the collector of TR614 are wrong.
At initial power up, C647 will begin to charge through R658. While it is charging, the base of TR615 will remain low and the collector will stay high. A high on the collector of TR615/base of TR616 will hold the collector of TR616 low. But this condition only should exist for a few ms while C647 is charging.
When the voltage on C647 exceeds the Zener on the base of TR615, TR615 will turn on, pulling its collector low. This will do two things.... First, the collector of TR616 will go high. It will also couple a negative going pulse into the base of TR614 causing its collector to momentarily go high. The high on the collector of TR614 only lasts a short time based on the charge time of C646.
So after the power has been on for a few milliseconds, I would expect the collector of TR616 to be high (pull up at the processor) and the collector of TR614 to be low (pull down R707 near the processor).
Most questionable is the fact you are measuring the collector of TR614 as a high. There should only be a short high going pulse at that point for at power on. And by short, I mean only about 1 ms. If it stays high, I would suspect a leaky C646. But that doesn't explain the low on TR616 collector.
So I am going to ask you to recheck the voltage on the collector of TR614, TR615, and TR616 when powered on and not working, and again after it starts to work.
Yes you are right, a short pulse on TR614 collector, Cold 0 volts a short pulse and 0 volts again. TR615 collector 3.6 V cold and 0.65 V warm. TR616 collector, cold 0 volts, warm 4.9 volts. I changed the capacitor C646 and it didn't change anything, the old one measured the correct value 1uF.
"TR615 collector 3.6 V cold and 0.65 V warm."
So are you saying that TR615 collector is at 3.6 volts after turn on and stays there until the unit starts to work after the warm up time, then dropping to 0.65v? During the turn on delay, can you measure the voltage at the positive end of C647?
So are you saying that TR615 collector is at 3.6 volts after turn on and stays there until the unit starts to work after the warm up time, then dropping to 0.65v? During the turn on delay, can you measure the voltage at the positive end of C647?
Yeah that's right, measured again now and get the same result on TR615. The capacitor C647 positive side shows 7.9 volts while it heats up and 8.9 volts when warm.
We are definitely in the right area. If we look at R658, one end connects to C647 that you just measured. The other end should be at about 19 volts per the schematic. Check that.
I'm thinking C647 is leaky. If you can lift that out of the circuit, you could check it with an ohmmeter. You could also try the unit without that cap and see if it comes on immediately or whether there is still a delay.
I'm thinking C647 is leaky. If you can lift that out of the circuit, you could check it with an ohmmeter. You could also try the unit without that cap and see if it comes on immediately or whether there is still a delay.
The capacitor C647 negative side shows 0 volts while it heats up and 0 volts when warm. I changed it but there was no improvement.
Is there +19 volts on the 'hot' end of R658? C647 should charge through R658 until it reaches the turn on voltage of the Zener diode ZD601. That should only take a few ms. Something must be holding it to 7.9 volts during the in-op time. BTW, looks like you got more test equipment than I do.
[The Zener is spec'd at 8.2 volts. That and the transistor B-E voltage of 0.7 volts gives the 8.9 you measured when working.]
[The Zener is spec'd at 8.2 volts. That and the transistor B-E voltage of 0.7 volts gives the 8.9 you measured when working.]
The R658 measures 14 volts when cold and 15 volts when warm.
So you like my little tester: https://www.ebay.com/itm/LCR-T4-Meg...itm=263829409906&_trksid=p2047675.c100623.m-1
I changed the C645 and it looks like everything is ok now,
I'll wait a bit until it's completely cold again.Now it has been standing for quite a while to cool down, starting instantaneously, problem solved. And again thanks for your patience and skillful guidance!
