Technics SU8080 Relay not Engaged
- Thread starter momolou
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That is correct if relay is not engaged. The protect circuit pulls one side of the relay coil to ground, causing the relay to engage. The other side is connected to -50 volts, so if nothing is pulling it up, both sides will have -50 on them.
Start by trouble shooting the protect circuit on the power supply board. Amplifier signal comes in on pins J10 and J11. If either is more than a volt, then you have an amplifier problem and protect circuit is probably doing its job. That is the most common scenario for no relay.
If both zero, Then check base of TR404. it should be about -1.4 volts. if less then check transistors TR402 and TR403. You can eliminate 402 and 403 as issues by disconnecting the collectors (should be center lead). If no issues, they should be in the off state and no current goes through them. They should only conduct if amplifier issues. if okay, check TR404 and TR405.
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That is correct way to measure. Means amplifiers are OK and troubleshoot protect circuit.
Check base of TR404. it should be about -1.4 volts. if less then check transistors TR402 and TR403. You can eliminate 402 and 403 as issues by disconnecting the collectors (should be center lead). If no issues, they should be in the off state and no current goes through them. They should only conduct if amplifier issues. if okay, check TR404 and TR405.
momolou
Active Member
thank you for your guidance, disconnecting collector 402 and 403 make -1.4volt appear and make relay engaged.
Just noticed one more detail for protect circuit.. Check the voltage at the base of TR402. It is supposed to be slightly positive (schematic says +0.25 volts). This is pulled up by the voltage coming from D401 and R403. There are no voltages on the schematics, but I estimate around 20 volts or so on the other side of R403. If it is low, could be bad cap C401. THis is basically an AC on circuit - the voltage drops rapidly when powered off and shuts the relay off before voltages drop on the main filter caps.
momolou
Active Member
with still disconnecting collector on TR 402 and TR 403 , there is no +0.25volt at the base TR402 , no 20 volts on other side R403
momolou
Active Member
from both sides of R403 , side connected to C401 = - 482mv ( negative ) , and side connected to base TR402 = - 654mv ( negative)
AC for positive voltage goes through fuse F7 and R502 (4.7 ohms) . Either one open will give you no AC to enable protect circuit.
The rest of the circuits will work even if they were open.
One more possibility. If one of the diodes in D509 were shorted, it would cause that fuse to go open, but rest of amp would run off other side of rectifier.
The rest of the circuits will work even if they were open.
One more possibility. If one of the diodes in D509 were shorted, it would cause that fuse to go open, but rest of amp would run off other side of rectifier.
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momolou
Active Member
yes, looked at fuse , the fuse open/burn , something make it open/burn , still looking this D509 where is actual location
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D509 is 4 diodes in one package. Since the fuses are 1/2 amp, any diode bridge rated at more than 1 amp and 100 volts will work okay.
You could cobble 4 diodes together, or use something like this. https://www.mouser.com/ProductDetail/Panjit/RDXK610_T0_00601?qs=pBunHO6%2BwtF4RUZ%2BfyQmvQ== \
The + lead goes toward the center of the board, the - toward the outside. The two AC leads are in the middle and can go either side. I would put some insulation on the middle leads.
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momolou
Active Member
Hi
i Am put new one fuse 500ml without touching old D509 Diode and measure AC voltage , i am measure with put negativ probe on 410 and positiv probe on 411 ,get value AC 82volt . It wrong ?
Hi sregor, thank you for this clue, i am measure this D509 still in circuit , in forward bias there is 0.5volt and reverse bias there is 2.0 volt, it is right way to determine diode rectifier is not short ?
i Am put new one fuse 500ml without touching old D509 Diode and measure AC voltage , i am measure with put negativ probe on 410 and positiv probe on 411 ,get value AC 82volt . It wrong ?
BIG apology. Didn't think completely about the circuit after D509. There will still be problems if one side shorted, (but the relay circuit will work....)
Disconnecting one side of input to D509 will still be problems with shorted segment, specifically to this supply. One supply will be okay, but the other has high AC on it because of shorted diode inside D509.
Verify DC voltages on D509 before adjusting regulator voltages.(outer pins, not AC pins)
momolou
Active Member
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Best guess is that short in d509 cause wrong AC voltage to lamp???
momolou
Active Member
i am take out D509 from circuit to test for short
1.
i am put Negative Probe on Negative side rectifier , and Positive probe on Both AC line Rectifier = OL ,
i am put Positive probe on Positive side rectifirer, and Negative probe on Both AC line Rectifier = OL
2.
when put Negative probe on Postive side Rectifier and put Postive probe on Both side AC line = 0.5volt
when put Postive probe on Negative side Rectifier and put Negative probe on Both side AC line = 0.5volt
it is correct way to measure short ?
result : no short ?
1.
i am put Negative Probe on Negative side rectifier , and Positive probe on Both AC line Rectifier = OL ,
i am put Positive probe on Positive side rectifirer, and Negative probe on Both AC line Rectifier = OL
2.
when put Negative probe on Postive side Rectifier and put Postive probe on Both side AC line = 0.5volt
when put Postive probe on Negative side Rectifier and put Negative probe on Both side AC line = 0.5volt
it is correct way to measure short ?
result : no short ?
Those measurements indicate no short.
A couple of questions. Did f7 fuse blow right away when replaced (before disconnecting one of the AC pins on D509) ?
If no short, then could there be a wiring issue. What are DC voltages on + and - pins of D509 in circuit with power?
Trying to get clues as to what is going on.
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