transistor question ....

mzeitlin3348

mzeitlin3348

See it and Believe
The service manual of my turntable calls for a 2SC1846-R transistor. Cross referencing listed an NTE-295.
I replaced it and my turntable stopped working where it worked before - as if little to no power. When I turned it on no strobe light and the platter barely moved. Clearly a problem.

I took a closer look at the part I removed and it wasn't a 2SC1846-R, but instead was a 2SC1846-Q. According to the cross reference, this calls for a NTE-373. This has very different specs.

Did I screw up? I went with the manual rather than the part on the board. Did I do damage or just go and replace the wrong part with the 373. Anyone else make this mistake? or is it a mistake (i.e. parts are interchangeable)
 
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Unless you have a strong reason to believe otherwise -- like you know someone's been hacking away at the board -- it's best to go with what's on the board, not the manual, unless the manual explicitly recommends alternatives to what's on the board.

Manuals sometimes don't match what's on the board for various reasons -- typos, circuit revisions that didn't make it into the manual, etc.
 
The only difference tween -Q and -R is gain (hfe)
Q:85～170 R:120～240hfe

2SC1846
Pc: 1.2
Vcb: 45 V
Vce: 35 V
Veb: 5 V
Ic max: 1 A
ft: 100 MHz
TO126

Someone can pop those values in a mouser search for you to find proper sub.
 
Thanks - guys. I'm so frustrated. I didn't think to actually look at the part on the board! It would have been so easy.
I just blindly looked at the service manual - went to my local parts store (benefit of living in a big city), bought the cross reference part (NTE295), installed it and ..... nada.
Checked the part I removed and started to say, *#$*@)#(*@)(*.

Gain is probably why the platter doesn't move and the turntable sits idle.
 
eizner23 said:
The only difference tween -Q and -R is gain (hfe)
Q:85～170 R:120～240hfe

2SC1846
Pc: 1.2
Vcb: 45 V
Vce: 35 V
Veb: 5 V
Ic max: 1 A
ft: 100 MHz
TO126

Someone can pop those values in a mouser search for you to find proper sub.
Click to expand...

Is the gain difference (IYO) sufficient to explain why the TT no longer works?
 
Why did you replace it? In general, never replace transistors unless they're bad, or are on a recognized list of flaky devices. You simply can't buy equivalents for most old parts today.
 
avionic said:
No..Either Q or R should do the job. Do you still have the original part? Check the pin out of the .....NTE versus the pin out of the original OEM part.
NTE is my bottom of the barrel , no other option available selection.:thumbsdown:
Click to expand...

I'll re-check. I thought the E-C-B pinout was the same.
 
ConradH said:
Why did you replace it? In general, never replace transistors unless they're bad, or are on a recognized list of flaky devices. You simply can't buy equivalents for most old parts today.
Click to expand...

I replaced it based on symptoms. The TT would run great for 20-30 minutes and then speed lock lost. Although I will be replacing the electrolytic caps, this particular problem seems related to heat up of the main voltage regulator feeding the speed control circuit. Another AK member suggested that they had this exact same symptom (run great until 20-30 mins then speed lock loss) and replaced this transistor - problem solved. I thought it was worth a shot. I love this turntable. If only .
 
eizner23 said:
The only difference tween -Q and -R is gain (hfe)
Q:85～170 R:120～240hfe

2SC1846
Pc: 1.2
Vcb: 45 V
Vce: 35 V
Veb: 5 V
Ic max: 1 A
ft: 100 MHz
TO126

Someone can pop those values in a mouser search for you to find proper sub.
Click to expand...

I tried buying a replacement and it's apparently wrong (i.e. values don't match above, yet the NTE373 is listed as a substitute). I need help here with what is the correct replacement for 2SC1846Q
 
Well ... this is interesting. I looked up the replacement part again from a different website (NTE-373) and there was a special note saying to make sure to install insulator.
Looking closely at the package, there indeed was a tiny wafer with a hole in it. So I unscrewed the NTE-373 and inserted the wafer in between the heat sink and the transistor.
Screwed the part down gently and plugged it in. Surprise surprise - turntable started working. Speed is locked.

I thought the purpose of the heat sink is to dissipate heat by directly coupling the device to the metal sink. Without the wafer material, I guess it was shorting out. Don't understand this. The original part had no wafer - it was directly coupled to the heat sink. Experienced hands on this forum may help shed light on this.

I'll know in 30 minutes whether this was my problem (speed lock loss). Still need to change caps down the road, but if this buys me time so I can enjoy vinyl again, I'll be happy.
 
I looks like what you now need to do is to get a tube of thermal transfer paste. Unbolt the transistor from it's heatsink and smear a little of the paste on each side of the insulating wafer. Now bolt the transistor back on to the heatsink with the wafer in between. This way you will thermally couple the transistor to the heatsink as the original one was.
 
Powertech said:
I looks like what you now need to do is to get a tube of thermal transfer paste. Unbolt the transistor from it's heatsink and smear a little of the paste on each side of the insulating wafer. Now bolt the transistor back on to the heatsink with the wafer in between. This way you will thermally couple the transistor to the heatsink as the original one was.
Click to expand...

Thanks, Powertech - I went ahead and did that.
 
mzeitlin3348 said:
Well ... this is interesting. I looked up the replacement part again from a different website (NTE-373) and there was a special note saying to make sure to install insulator.
Looking closely at the package, there indeed was a tiny wafer with a hole in it. So I unscrewed the NTE-373 and inserted the wafer in between the heat sink and the transistor.
Screwed the part down gently and plugged it in. Surprise surprise - turntable started working. Speed is locked.

I thought the purpose of the heat sink is to dissipate heat by directly coupling the device to the metal sink. Without the wafer material, I guess it was shorting out. Don't understand this. The original part had no wafer - it was directly coupled to the heat sink. Experienced hands on this forum may help shed light on this.

I'll know in 30 minutes whether this was my problem (speed lock loss). Still need to change caps down the road, but if this buys me time so I can enjoy vinyl again, I'll be happy.
Click to expand...
The reason you can read from the datasheet: the original did not need an insulator as stated there.....https://alltransistors.com/pdfview.php?doc=2sc1846.pdf&dire=_panasonic
 
gslikker said:
The reason you can read from the datasheet: the original did not need an insulator as stated there.....https://alltransistors.com/pdfview.php?doc=2sc1846.pdf&dire=_panasonic
Click to expand...

"TO-126B package which requires no insulation plate for installation
to the heat sink"

I didn't see this ... thanks - now I understand why it didn't work. There was nothing wrong with the part or the cross-reference. It seems the OEM TO-126B packaging is better? Can you recommend a better quality transistor than NTE? I am reading that NTE is low quality and I would rather put a better quality part in place of the OEM so it's "done" right. Thanks
 
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