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Old 10-15-2018, 10:37 AM   #21
duharris
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Default Re: Norstar NT5B01 power supply

I've got an NT5B06 unit (from label NT5B01FD-93) that I'm trying to keep alive for the business I work at. The unit is in hot computer rooom, where the temperature is elevated (an issue in itself). The unit will stop working when the room is hot...I discovered I can keep the door to the room open and use a box fan to blow cool air into the room and the unit will start to work...at first, it would work a few minutes then shut off (blinking triangles on the handsets), then, I unplugged a few handsets and kept it cool and the system will not work continuously now. I haven't been able to put a scope on it, but was going to replace D75 and D78 since they had the large heat sinks on them...but I can't determine what kind of replacement diodes I need for these....anyone have a part number for these? Or, any additional hints to help me keep this unit alive?

Thanks in advance!
D. Harrison
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Old 10-19-2018, 07:41 PM   #22
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Default Re: Norstar NT5B01 power supply

Could you upload a high resolution picture of the power supply area here? I don't think it is the diodes. These Norstar phone systems have 2 voltage rails, a 5V and a 19V rail. Measure them before and after a failure. Does the power led on the unit blink on and off all the time?
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Old 04-08-2019, 05:07 PM   #23
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Default Re: Norstar NT5B01 power supply

I guess it's been a while since I have had an NT5B01 to repair. Anyway here it goes:
I've got an NT5B0139 here on the bench. Complaint, phones wont boot, but the power supply LED is on. Everything looks in order as usual. I look at the 19V and 5V rail with nothing attached and all looks good. Then I hooked up one phone on it and the 19V rail went lower in voltage. Replaced the startup cap C241 and two filter caps C194 and C213. Everything is A1 again and another happy customer. I guess these things go like forever, compared to them BCM50's.
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Old 05-03-2019, 06:38 PM   #24
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Default Re: Norstar NT5B01 power supply

Had another NT5B01 here that would blink the red PSU LED after 10 to 15 mins. Since it failed after it ran for a bit, it had to be an IC. Went looking with my desoldering station and found the PWM clunking out as soon as it got warm. Changed the PWM and all is good again!
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Old 05-31-2021, 08:44 AM   #25
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Default Re: Norstar NT5B01 power supply

Well... boring COVID-19 shutdown case: Got one of these old Nortel NT5B01 6x6 phone systems in again for repair.
Symptom: Phone system appears to be dead, no Power LED.
Fix: Traced it to be a D64 P6KE27A TVS protection diode shorted to GND on the 19V rail. This is the second one that done this. Replaced that TVS diode and all is A1 again. These old buggers just don't want to die!
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Old 06-01-2021, 12:48 PM   #26
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Default Re: Norstar NT5B01 power supply

Compared to gas discharge tubes and even MOVs, TVS diodes are fast. But their energy handling capacity is not as great.
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Old 06-01-2021, 04:44 PM   #27
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Default Re: Norstar NT5B01 power supply

well, it also depends on in what circuit you are trying to protect. In this case the TVS is fine as kind. It just protects the 19V rail. That will over current the PSU, it protects itself and turns off. It's not like the TVS diode is directly at an input protecting something.
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