Help identify this component please

“Q” is the standard designator for a transistor.

You can check resistors on almost any basic multimeter. Capacitor and transistor tests are on some multi-meters.

For simple circuits, it’s very rare for a resistor to fail, a little more common for a capacitor to fail but not if it’s a ceramic or film capacitor, it’s most common that the transistor failed.

Often a transistor used for driving a relay will cost less than 25 cents. Also inexpensive transistor test functions do not give the most accurate results, so often techs will simply put in a new transistor and see what happens.

I wonder if I should find a replacement transistor while I wait for this relay to come in from China…thing is I threw voltage at it and heard it click while simultaneously testing continuity at the contact side of relay…so I do think relay is shot…but perhaps I am dealing with a bad transistor(s) as well if I am only getting 6 volts on that one side of the coil…

If you can identify the make/model and buy the transistor for only a small amount it could save total repair time. (of course if you can’t identify it let us know the markings and we may be able to ID it)

If you end up not needing it, you’ll have a good new part for your electronics parts box.

This assumes you’re now addicted like me and will want to play with electronics hardware for decades to come. When I go through my parts collection I still encounter and smile about parts I bought 30 years ago for repairs/upgrades but didn’t end up needing.

If you start a parts collection a good way to learn a lot is to remove parts from non-repairable devices without damaging them and test them for re-use in other things. When I was a kid I designed & built whole gadgets with recycled electronic components (the first was a battery tester circa 1968).

I got the relay in the mail and now I’m about to desolder and solder for my first time. What would you recommend for the size diameter of rosin for this relay?

For me, the diameter of the solder is not important, other than cost.

To save money I use the largest solder that works without leaving a mess that needs partial removal.

Generally for large PCB mounted parts that’s, 1/32" diameter solder.

I find Sn60Pb40 (60/40 tin/lead) or Sn63Pb37, rosin flux core solder to make the easiest and best quality solder joints

Thank you for all your help. I really hope this new relay does the fix

After watching a video on transistors I’m learning more…I think the fact that one leg of my relay is getting 12v and the other is getting only 6v and not the full 12v is because of potentially a bad transistor…or power to that transistor…definitely still a little tricky but transistors I guess are never supplying ground voltage and only supplying positive voltage…if I only get 6v when I should be getting 12v then the transistor could be bad or whatever is feeding the transistor is bad

Sort of…

In the classic transistor relay driver it is attempting to supply ground. If an ideal transistor existed it would switch the low side to ground.

However nothing comes even close to an ideal component in electronics. So instead the circuit has to make do with switching close enough to ground to make the relay turn on reliably.

The circuit designer has to balance cost, lifetime, energy consumption, and other factors. If we had the designers schematic for the circuit it might say what the low side on voltage is supposed to be. At a minimum we could calculate out a close enough value from the actual circuit component values.

This reference has more details on typical relay driver circuits:
Relay Switch Circuit and Relay Switching Circuit

1 Like

“When the circuit drives the relay coil down it is usually to within 1V of ground. However to save costs a designer of a consumer grade circuit can let that end up higher as long as it meets the relay manufacturers spec.”

So the coil is driven down in voltage to activate it…I wonder since I’m getting 6 volts instead of <1 volts that I have an issue with a transistor not performing or possibly a signal component is bad like a thermostat or something that is TELLING the relay to turn on…without a schematic we are both in the dark unless I can do a really good job tracing all the components on the board…

Hey Paul…so here’s an update…I put in the new relay and everything was good and working…wine cooler got to temp and stayed…then the temp stabilized and the compressor turned off…when it went to turn back on I heard a terrible rattling/chattering sound…I actually saw sparks coming from inside the relay…I don’t know what to do now and what component(s) to test and how to test them…

I’m narrowing the problem down to a few possibilities but don’t know where to go as far as troubleshooting…

  1. Transistor fault causing weak magnetic field and contacts not connecting strong enough

  2. Relay coil keeps turning on and off for whatever reason causing the relay contacts to chatter and therefore spark like crazy as the contacts get close to each other repeatedly…

  3. Compressor is going bad and drawing too much amperage

I’m leaning towards #1 or #2 because of the fact that I was seeing only 6v at the side of coil where the transistor collector is when I should have been seeing a full 12v…am I right in my thinking of what I need to look at? If so, how would I go about troubleshooting these components to correct the problem and get this running right again?

Nice troubleshooting.

I think #1 is most likely and easy to test by replacing the transistor.

The other resistors, capacitors, diodes, etc. in the transistor switch circuit are very unlikely to fail and when they do they most often looked burned.

Very cool thank you!

So the transistor drives the relay by grounding it completely and not actually providing power right? I have been reading about it…it gets .7v to activate the base and then that allows the coil to be grounded and basically what turns on and off the relay? If a new transistor doesn’t fix it…is there a possibility that the driving circuit of .7v to open is disturbed? What would control that? I tracked it back and saw that it gets its power from a red wire in a harness that is labeled comp for compressor…does the thermostat give this .7v when it senses the temperature change to kick off the whole process of cooling again?

When changing the transistor I’m assuming ALL numbers are important not just the first set?

Mine is c1815 gr011

Not sure if I can replace with any c1815 or do I need to get the one that says gr011

Ok Paul I’m back haha…I just did another test…I definitely think low coil voltage is 100% my issue here…I am getting 12 vdc on supply side still but only 6vdc at the coil side still…new relay is working because it hasn’t fried yet…

Anyways I just tested base voltage at the transistor and got only .5 volts!! I was under the impression this should be at least .7v to fully activate the relay coil…

Now that I know I have low supply voltage to the transistor base…what would/could cause this? Could it still be something internal in the transistor causing it to bleed down? Or could it actually not be the transistor and be something that is “feeding the transistor”

Most often a transistor will be marked with a part number and a lot code. The part number often is a single letter then 2 to 4 digits representing the JEDEC or JIS standard numbering systems.
N = 2N series from JEDEC
A, B, C and D = 2SA, 2SB, 2SC and 2SD series from JIS

So for your part it is most likely a 2SC1815 and GR011 is the lot code.

I found it on DigiKey, looked at the data sheet, and to my surprise this is one of those odd ducks that is available in 5 variations of gain. blank, O, Y, GR & L. So yours is the GR variation and the DigiKey part is the blank variation so not suitable. :frowning: If you wanted to buy 6,425 pieces they could get them for you through Rochester.

I only found one US purchasing option in my limited search, 100 pieces of 2SC1815GR for $5.99 via Amazon seller Ywhome.

I guess there is a manufacturer in China turning out bucket loads of this part for local manufacturing. Often those parts are not available from normal US electronics distributors. So you may find a smaller quantity for less money from one of the, hit or miss, direct from China, component retailers.

If I had to buy a hundred, the specs on that transistor are very good compared to my normal go to small transistors, the 2N3904 and 2N2222, so having 99 of those to use for substitutes, experiments, and project builds would be good.

You are correct, in fact it’s more common to see a base voltage of > 1 volts and for better switching action it’s common to push the base to 5 or more volts for the on state. Transistors used as switches like to be driven fast and hard because any time spent at not fully on or fully off wastes power generating heat. The state where the transistor is not fully on or off is the linear region and in a switching application we want digital action not linear. Amplifiers on the other hand distort the output when full on or off so in that application you want the base voltage to be well within the linear region.

It could be the that the transistor is damaged and drawing excessive base current. To test just measure that voltage with the transistor removed. If it reads much higher when out than in, then the transistor is bad.

If that isn’t the problem it means the part driving the transistor is bad and that might be almost impossible to replace because it’s often a micro that requires custom programming and there usually is no practical way to get that code. Let’s not cross that bridge yet cuz hopefully we won’t have to :crossed_fingers:

Thank you once again Paul for your clarification! Just in time because I’m getting sleepy and need a good night sleep after thinking about this all day long…now I can rest at ease and order a transistor…just found exact match on ebay…the one you sent me I rather get it if it is 100% compatible because it would be here sooner…my collector is in the middle and I’m not sure that one is…it doesn’t say gr011 on it…not sure how important that lot code is to match…

So when you say the transistor could be bad drawing excess current…that would mean that the transistor is drawing excess current and “stealing it” from the base resulting in a lower than desired base voltage…I think all that’s left to do it remove the transistor from board and do some more tests on it…specific multimeter tests that I have read about which are not accurate while it is on the board still…much more accurate when it is off the board.

I checked out the one you sent me from amazon…it just says gr and no number after…my concern is getting the wrong one where the collector is in a different location than mine and it won’t work…looking from underneath it is base collector emitter…well depending on which way you have the board turned…either way you get my question…could I rest assure that it will be in the right orientation?

The data sheet says that only the letters O, Y, GR & L are used to designate the higher performance grades.

The numbers after the “GR” almost certainly reflect manufacturing date, location, or a combination of both.



None of the 2SC1815 data sheets I looked at showed manufacturing date/location codes. When there is enough room on the housing, semiconductors will usually use the ECIA standard 4 digit date code (year & week as YYWW, today we begin 2324).

But on a tiny package like the TO-92 4 digits often won’t easily fit in production so they use a shortened code. Unfortunately there are many variations of three digit date code systems. Assuming the product was manufactured in the last 5 years some good guesses would be 11th week of 2020, November 2020, 1st week of 2021, January 2021.


Given the simplicity of relay driver circuits I’m actually surprised the part has such a high guaranteed hfe specification. It’s quite possible that those just happened to be the cheapest parts available when they ordered them and any hfe grade will work.

The way it usually works with performance grade classification is that they test on the production line and sort parts by grade before marking the parts. Then when they need to ship parts they sometimes end up grabbing better parts and label them as lower spec to make a quicker sale at a reduced profit margin (due to inventory time costs, sometimes a lower margin now means more profit for the quarter).

So it’s very possible when someone buys a loosest spec part (blank code) they actually get a better grade part. This is what lead to the belief by many non-engineers that they can buy any low speed grade microprocessor, overclock it, and it will be reliable. The reality is it’s a crap shoot when you overclock.

Thanks again Paul. You are a wealth of knowledge…

My concern is the arrangement of the base collector and emitter…my setup is collector being in the middle and not base…I guess I can just turn it around worse case scenario as long as collector was in the middle…do all these c1815 gr transistors have the same orientation as far as location of base emitter and collector?

Also want to add that I have been testing everything on this board and since I don’t know anything about what is a passing spec on it I just compare the components to the relay that is not causing me trouble…I have the relay next to the problem relay…it is for defrost heater but has same components in the drive circuit as the relay that is causing me trouble…

So the only difference I have seen so far is the diode on the relay that is causing me issues is .274 and the diode on the good relay with no issues is .317…

Not sure what this test exactly does but it is the diode test function on my multimeter…