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I think it's a Diac but can't cross reference!

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Electrifly

New Member
I consider myself as newb in electronics so I need your help

I have a multimeter I am trying to repair. Apart from the fuse, another component blew which has a Diac symbol on the PC board and the markings on the component are: 7 L391 1G (see attached pics)

diac 2.JPG DIAC.JPG

Nothing comes up when I do a search. Can someone tell me where I can get these DIACs or give me a cross reference to another.

Thanks in advance.
 

ericgibbs

Well-Known Member
Most Helpful Member
hi E,
Having a Diac in a multimeter is not usual, I would say its a voltage transient suppressor.
What were you measuring when it blew.?
E
 

Electrifly

New Member
Thanks for responding Eric.

The meter was set to resistance but the terminals touched 380V AC - pop followed by that ever hateful stench of fried electronics.
 

ericgibbs

Well-Known Member
Most Helpful Member
hi,
I also cannot find a match for that part number.
I would try the following, remove the blown diode, clean away any carbonised track on the PCB.

Put the meter on ohms range and check the meter for correct resistance operation, there maybe other damaged components.

What is the meter model number.?

E
 

Electrifly

New Member
It's an oldie - Micronta 22-167.
Might not be worth much except for the repair challenge.

I'll measure what you asked for shortly.
 

Electrifly

New Member
Hey Mickster...
Thank for the link. My typical method now to go to Digikey or Mouser cross reference this Z7L391 Metal Oxide Varistor unless you know of another source.
also, please correct me if i'm wrong, is a Varistor the same as a DIAC and should my search be for a Varistor?
 

Electrifly

New Member
Dah....... MOV -Metal Oxide Varistor.

I answered my own question - didn't even see it.

Thanks to all for your help. I should be able to take it from here.
 

ericgibbs

Well-Known Member
Most Helpful Member
hi E,
Have you done the simple test I suggested in post #4 , checking for more damage.?

is a Varistor the same as a DIAC

No, it's a totally different animal.;)

E
 

RODALCO

Well-Known Member
A diac is not a MOV.
A diac is used in a light dimmer to trigger the triac.
Diacs break down at about 32 Volts.

More likely that a MOV had blown in your multi meter.
 

ericgibbs

Well-Known Member
Most Helpful Member
Looking at Eric and looking around the ETO room. He is long gone...whom are you talking to? lol
hi EG,
I do not understand what you mean, the Thread is current for this week.?
Eric
 

Electrifly

New Member
Sorry for the late response.
I have cleaned the board, replaced the fuse and did a few tests. As E requested, the meter comes on, but does not respond to voltage and resistance
It is/was an MOV that blew and a new one with the same specs was ordered through Mickster's help.
When the new component comes in, I'll solder it in and feed back with the results.
 

ericgibbs

Well-Known Member
Most Helpful Member
I have cleaned the board, replaced the fuse and did a few tests. As E requested, the meter comes on, but does not respond to voltage and resistance
hi E,
That is bad news.:(
The MOV only comes into play when the input exceeds the safe limit, so the meter should work without it.
E
 
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