Diode symbol I've never seen before

Thread Starter

shortfuse13

Joined Apr 7, 2023
9
Wondering if anyone had ever seen the diode symbol in the pic below at d105. I've never come across it and found it odd enough to want to create an account and post it see if anyone else has ever seen it this is on a pioneer laser disc player probably from the late '80s early '90s that I'm playing with just as a project. Text on the board clearly she says that it's a diode but when I run it through my tester it seems blown showing up is just a resistor of about .3 ohms. I'll post a picture of the diode as well.
 

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debe

Joined Sep 21, 2010
1,388
Its a Transient Voltage Protector ( back to back Zenner diode). Come in a range of voltages. If shows as a short it has done its job, they are a protection device against HV spikes.
 

Thread Starter

shortfuse13

Joined Apr 7, 2023
9
Ah any advice on figuring out reasonable values for replacement component? Measure voltage across those two points with it removed ?
 

Analog Ground

Joined Apr 24, 2019
460
One idea. If it is a protection device, the circuit might very likely work without it. Not protected but functional. Have you tried operating without it?
 

Analog Ground

Joined Apr 24, 2019
460

Thread Starter

shortfuse13

Joined Apr 7, 2023
9
Ah excellent info thank you very much, I managed to track it down with a multi meter initially and circuit looks good from an ohm perspective with it removed. Once I get a new fuse and don't other bits we'll find out.
 

debe

Joined Sep 21, 2010
1,388
It apears the original UK1V26 is only 265V TVS & was a problem. Sugested size is P6KE350 TVS diode as a replacement.
 

MisterBill2

Joined Jan 23, 2018
16,569
I had a TVS failure in a TV set many tears back, and not realizing that was what popped the fuse, I replaced the fuse and it immediately popped again. That time the TVS also showed signs of failure, and after I traced it out in the circuit, I removed it and the TV worked quite well as I was unable to locate another TVS device locally.
Several years later another line transient took out the CRT high voltage regulator, and so I used a 24 volt transformer in an auto-transformer scheme to run the set on 95 volts, which did not trip the over-voltage circuit. We used that for several years.
My point being that a TVS can be helpful but they mostly seem to protect by latching in the shorted circuit mode.
 

Thread Starter

shortfuse13

Joined Apr 7, 2023
9
That looks like exactly what happened here. With it installed the entire primary side resistance reads around .8 ohms, removed it's around 1m ohms.
 

AnalogKid

Joined Aug 1, 2013
10,786
Vishay purchased General Semiconductor's TranZorb line. Littlefuse lso picked up some. Part numbers with a C on the end are bi-directional, for AC applications. TP5K, TP6K, and TP1.5K are the most common through-hole parts.

https://en.wikipedia.org/wiki/Transient-voltage-suppression_diode

https://www.littelfuse.com/industries/automotive/semiconductors/tvs-diodes.aspx

Here is waaaay more than you ever wanted to know about them.

http://www.reallyreallyrandom.com/zener/media/Zener_Theory_and_Design.pdf

ak
 

Thread Starter

shortfuse13

Joined Apr 7, 2023
9
Thanks for the help all, still trying to find something available to replace it. I do have some 300 watt unidirectional tvs diodes, can I just solder two of them together and get the same effect?
 

MisterBill2

Joined Jan 23, 2018
16,569
Thanks for the help all, still trying to find something available to replace it. I do have some 300 watt unidirectional tvs diodes, can I just solder two of them together and get the same effect?
NO!! Not unless the voltage rating is correct.
I have not seen any verification that the device that the TVS was in still is functional or not.
With the TVS removed and the device assembled, and the fuse replaced, the TS should be able to verify that it operates correctly. If it DOES work right, then it is worth the effort to replace the device, if not, additional diagnostic effort will be required.
 

Thread Starter

shortfuse13

Joined Apr 7, 2023
9
I haven't tested the full device yet but the tvs was bad. With it removed it draws almost no current, with it installed it good to the limit on my current limiter. Without the limiter it blows the fuse with the tvs installed. I'll throw it back in and test.
 

MisterBill2

Joined Jan 23, 2018
16,569
There is no reason to test with the failed TVS device in place!!
The TVS is a protection device, not an active component. So I was, and still am, suggesting checking with the failed TVS disconnected. I anticipate that the operation will be satisfactory.
 

Lightium

Joined Jun 6, 2012
117
Ah any advice on figuring out reasonable values for replacement component? Measure voltage across those two points with it removed ?
It's best to trace out the circuit around the area you found the TVS diode and look for what it was protecting and limit the voltage based off of the datasheet for the protected component.
 
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