I need a value for a shorted zener diode in a CRT monitor, please help

I need help replacing a Zener diode that is shorted. it connects to a NPN silicon power transistor 2SD1018. The Zener diode is between the base and emitter. I was woundering if someone was to look at the data sheet for the transistor and how the Zener is located on the PCB someone might be able to tell me the value of the Zener I’m replacing. The data sheet says BVebo (emitter to base breakdown voltage) is 5.0 volts so, I’m guessing the Zener is a 5.0 volt Zener; however, I’m just guessing.

datasheet: https://www.datasheets360.com/pdf/5834349051354430101

thanks in advance :smiley:

Hello mcgagheyj, welcome to the DigiKey TechForum.
My guess is also that it would be a 5V Zener, to limit the voltage going to the base pin.
Hopefully, one of the engineer can add to this post, and help verify what Zener is being used in your circuit. Can you post pictures of the zener diode, and any numbers on it?

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David_1768: thank you for the response, I don’t see any part number, or markings on the zener doide; however, I have pictures of it

Is that a horizontal output transistor? It sure looks like one on that heatsink and if it is you should check out the parts in that area for over heating or cold solder joints. Horizontal output circuits are notorious for catastrophic failures and I have seen more than a few of them when I worked as a TV technician many (many) years ago. I also agree it’s likely a 5V (5.1V) zener.


Good morning, Gromit thanks for your response, this is not the horizontal output transistor. This is part of the voltage regulation circuit. This is a Toei TC-V814P Monitor from 1980’s. I have checked all surrounding components, e.g., resistor values, diodes, transistors, non-electrolytic capacitors and replaced all electricality capacitors along with the B+ pot. I have no schematics.

I’m grateful to David_1768DigiKey Employee and Gromit for assisting me in repairing our treasured “Mini Vegas 4in1” Japanese Video Poker Game from 1983 Entertainment Enterprises, Limited. Now, at 41 years old in 2024, it has quickly become a beloved addition to our family favorites.

The problem originated from a faulty power circuit in the Toei Model: TC-V814P; 100V AC (isolated) monitor. The previous owner mistakenly plugged the 100VAC monitor into a 117VAC wall outlet without an isolation transformer. This caused damage to the bridge rectifier, vaporizing a trace, and affecting several other components in the power circuit.

To address the issue, I focused on the power circuit, taking the following steps:

  1. Replaced all electrolytic capacitors.
  2. Installed a 5K potentiometer for the B+.
  3. Inspected and tested around 25 resistors, replacing seven that were out of specification. Knowing resistor color codes helped speed up this process.
  4. Identified and replaced a shorted Zener diode between the base and emitter of the NPN power transistor (2SD1018) at D24 in the power regulation circuit. The lack of markings on the Zener diode required some research, and with guidance from David_1768DigiKey Employee and Gromit, I selected a replacement with a reverse voltage of 2 volts, correctly oriented.
  5. During the monitor’s power-up, I also had the chance to test my new InfiRay P2 Pro thermal camera for the first time. Components were observed to be operating within normal temperature ranges.

Once again, thanks to David_1768DigiKey Employee and Gromit for their help throughout this repair.

Working game: https://youtube.com/shorts/erAwb1sS-xI