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Transistor Testers

LBPete

LBPete

Rolling Along
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How useful is a stand alone transistor tester? I'm pretty much a novice at trouble shooting electronic circuits and these testers look like a handy short cut for the electronically challenged. The common ones are B+K and Sencore. These testers appear to have been popular in the past and now I see a lot of inexpensive DVOMs with transistor test functions. Are any of these capable of truly testing transistor function in a circuit. Are there specific features or models I should be looking for? Can they be used to test and match transistors?

Thanks,

- Pete
 
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Most simply allow you to verify basic functionallity, and give you a figure for hfe. The B&K 815 (which I'd like to have) is supposed to test for leakage also. How well that function works, I dunno.. I still want one.

And yes, they are good for matching transistors. Not as good as a curve tracer, but for small signal devices they work great. I have a super-el-cheapo meter with gain testing on it (all I use that meter for), and I use it all the time to match transistors for diff input stages.
 
For any of you DIY types or just anyone wanting to understand how a transistor tester works (and hence how transistors work or not!) here is a very nice project with an excellent write up on application.

Keep meaning to start trying to aquire parts and build one, but you know how that goes (first got to find a ROUND_TU_IT) :p:

http://sound.westhost.com/project31.htm


Lefty
 
Originally posted by EchoWars
Most simply allow you to verify basic functionality, and give you a figure for hfe. The B&K 815 (which I'd like to have) is supposed to test for leakage also. How well that function works, I dunno.. I still want one.
Click to expand...

EW, it looks like the B+K 815 is strictly an out of circuit tester. I've been eyeing an older model, the B+K 520B. It looks simple and claims to test both in and out of the circuit. In looking at the specs, it does test leakage but I don't see any reference to gain/HFE/Beta.

Where I'm going with this is the driver boards on my G22k. The right side is showing almost half a volt (0.5v) on the output. I would like to test the drivers. I'm also having trouble sourcing quality replacements. It uses one of each:
2SC2071
2SA939
2SC2238
2SA968

Any recommendations? Most places cross them to NTE numbers.

Lefty, thanks for the reference. I also have trouble getting a "round tuit." That's why I'm looking for something ready to roll out of the box.


- Pete
 
If you have bad offset, you're looking at the wrong end of the amp. Chances are good that the triple-Darlington output is simply doing its job. What's more, the type of leakage necessary to get 500mV of DC output on a driver stage with the huge supply voltages on something like a 22K amp is extremely unlikely to be found with any handheld tester.

I'm assuming here that you've attempted to adjust the offset pot. If so, did it do anything at all? Pray that the FET isn't the problem, you'll play hell trying to find a 2SK129.

Offset is cured at the input of the amp (providing nothing is totally borked). Since this is a FET input amp, look to the next stage. Sansui uses an 'X' balanced cascoded VAS stage after the input, with 2C1775's and 2SA872's. Replace them all...they're cheap.

You also need to check all ground connections to the driver board...it wouldn't take much to result in 500mV of offset.

Other than the FET, appears that Colsolidated carries about everything else.

http://www.ceitron.com/

There are also transistors sold by Digikey that would work, but if you can get the proper ones, don't bother with replacements (and with the 'X' balanced design, if you put in NTE devices, it would not suprise me a bit if it blew up as soon as you applied power:eek: )
 
EW,
I haven't played with the bias adjustment yet. Even with the light bulb variac, I'm a little gun-shy about powering this unit up with that much offset. Maybe I'm just paranoid. When turned on, it takes a very long time to come out of protection, but it does eventually.

Thanks for the information on the transistors. Those suckers are cheap, 25 cents!

I spent some time this evening tracing the ground circuits. Not a simple task trying to match the lousy photocopy Sansui schematic to the actual board. I found 4 ground points on the driver board. Two are on the ends of the large multi-pin connector and the other two are on the small connector. I need to pull the power supply board to trace the ground back to it's source. I can't see enough of it installed.

Everything looks good visually. I'm thinking the best way to check it is to measure the ground level with a voltmeter. Placing the negative probe on the ground source and the positive probe on the appropriate ground traces on the driver board. I'm not sure what the normal ground level should be, but I should be able to compare the left and right channels. Only trouble is, the unit has to be powered up.

By the way, here is a source for the FET.

http://www.partsolver.com/SearchResults.asp?SearchType=PartNumber&PartNumber=2SK129

It never ceases to amaze me what can be found with a simple search of yahoo. All I did was enter 2SK129, and the first listed hit was a bull's eye.

Thanks again for your help. I've called the pope and recommended you for saint hood!
 
Just a warning...PartSolver shows a lot of parts that are NLA. However, the problem is likely elsewhere if it'll pass a signal.

Yes...simply measure the voltage difference between a honest-to-goodness good ground, and a supposed good ground point on the drivers. 500mV certainly indicates a problem, but should not blow anything up...
 
Checked the ground level on the driver board grounds and they are very low. So the grounds are good. The DC on the output dropped right down to near zero just adjusting the trim pot. I wouldn’t have thought that trimmer would have that much range. After turning it off and back on the output DC voltage was back up to just over 0.1 volt, but it adjusted back down to near zero with the trimmer. I'm guessing that it will take a few cycles until it stabilizes. Is there any harm in squirting a little de-oxit into the trimmers?

The right side is still distorted, but it changes noticeably when working some of the switches. So the next phase is to tear into the tuner/preamp and clean the controls.

- Pete
 
DeOxit won't hurt the trimmers at all...and most DC offset pots will easily allow you to adjust enough to trip the protection circuitry (1.5 - 2V).

FYI, turn in on, adjust offset, and walk away for an hour. Come back and adjust it again, then leave it again for a while. Do this a few times, and then leave it alone...you're done. The offset reading you get when you first turn it on is not the one you need to be concerned with...only the reading you see after its been on for an hour.
 
EchoWars said:
I have a super-el-cheapo meter with gain testing on it (all I use that meter for), and I use it all the time to match transistors for diff input stages.
Click to expand...

What is the make and model of this meter? "Super-el-cheapo" is music to my ears.

I'm reviving this thread because I know that sooner or later another one of my herd will require a transistor transplant, and I'll need to match a pair of transistors.
 
I'm the one who dug this old thread up. On doing a search for transistor testers, I found it, and EchoWars' reference to a cheap (hallelujah!) tester that does the job. EchoWars should certainly know what he's doing with something like this.

However, if other people have ideas for inexpensive testers that can peform gain testing to match transistors for differential input pair applications (or any others), then that'd be a plus.

In retrospect, I think what I did is a little confusing, and I should have just started a new thread.
 
shocley said:
I'm the one who dug this old thread up. On doing a search for transistor testers, I found it, and EchoWars' reference to a cheap (hallelujah!) tester that does the job. EchoWars should certainly know what he's doing with something like this.

However, if other people have ideas for inexpensive testers that can peform gain testing to match transistors for differential input pair applications (or any others), then that'd be a plus.

In retrospect, I think what I did is a little confusing, and I should have just started a new thread.
Click to expand...

I made one from a kit (in Australia) https://secure4.vivid-design.com.au...2=K&pageNumber=&priceMin=&priceMax=&SUBCATID=

and it seems to work fine in circuit, though once it got confused for reason I didn't understand (but EW did :-/

I still think its a reasonable first-stab for a novice.
 
Keep looking...you might be able to find something cheaper and even more useless.

C'mon guys...what is the deal? Exactly how do you decide that "I need a piece of test equipment, but my max spending limit is $5.00" ??

You don't have to break the bank here to get something that'll do the job.
 
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