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A Better Option Than DCA55

TheRealPorkchop

TheRealPorkchop

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Aug 25, 2015
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I’ve got the Atlas DCA55 to test transistors, I’m not too impressed with it, not for the price. It’s not terribly expensive but it’s not cheap either.

I’ve found it to be a huge liar, maybe I got a dud, I don’t know, maybe I just don’t know how to use it either.

Recently, testing the first IF amp in a receiver, this thing shows the transistor as being good. The part is a 2SC1674 but the receive is very weak, basically not even there. Lifting the collector, you can faintly hear the tone being injected. So at this point, I hunt for another possible cause, something that has to be wrong to pull that collector down. But there’s nothing wrong except this one part, the 2SC1674.

Hunting for one in the parts bin, changing it out, presto!! The receive comes back to life. It also works with a 2SC945 in place or a 2SC1675. I have plenty of 945’s and 1674’s that I bought from Mouser but they are absolute turds and worthless. Every 1674 I put in, useless, no more receive than the bad part. Same thing for the 945 part. Lesson learned for buying those from Mouser.

So my question, if you’ve stuck around through all that jibber jabber, is there a better tester that is affordable? Or, am I using the thing wrong or overlooking the numbers it’s giving me?
 

Remember the RF pre-amp thread - I came across several different PDF's that were from the different MANUFACTURERS of that same part, but some had their pinouts wrong.

Some were BCE one was ECB - so if the Atlas is showing you one thing - just remember that the pinout needs to be paid attention to too. Because what I thought was a conventional system - is not - they makers of these parts can identify as the type of part it is performance wise but not necessarily by pinout or even case design (TO-92 versus Giant TO-92).

But then, to me, performance is also meaning that the part is pin-for-pin replacement too.

Now? Who knows?
 
Well the DCA says the pinout is the same, I thought about that too and I made sure to double check it. So far as I know, they’re the correct pinout.

The 945’s, in the transmit/receive switching circuit, I’ve had blown 945’s that I put these into and still the same issue. Went to the parts bin and snatched one out a radio, worked like a charm. And the DCA says those are the same pinout also. So I don’t know.

I do know this, I’ll only buy those two parts from RF Parts from now on, lesson definitely learned.
 
I have a Sencore TF30 super cricket. I've only used it on 2879s, 1446s, and 2290s but it seems to be reliable. I have no experience with the dca testers.

The cricket testers were going for a pretty penny on ebay at one time but I finally snatched one for around $25.
 
Those transistor checkers are good for basic tests... like does it look like a transistor, etc.
Also for the unknowns - what does it think this part is..

Not sure why you can't get a good portable tester anymore.
Probably because it can't fit in a pocket.
I still have several made by Leader like the LTC-906 and 906A that I use all the time.
I have a super cricket someplace - also a fantastic tester.
If I want to know if it really works I use a Tek 577 or one of the Leader or Sencore transistor testers.
They can actually stress the device, which the Atlas cannot.
 
543_Dallas said:
I have a Sencore TF30 super cricket. I've only used it on 2879s, 1446s, and 2290s but it seems to be reliable. I have no experience with the dca testers.

The cricket testers were going for a pretty penny on ebay at one time but I finally snatched one for around $25.
Click to expand...

I’ll look into that. There’s a better way I’m sure. Better quality parts is also part of the problem here. Thanks.

sonoma said:
I bought one of these a few months ago and it seems to work just fine. it either shows the part as good or bad. about 4 years ago I bought the internal guts for 3.00 and put it in a box and it works good also.
when the one I am leaving you a link for came out I bought one of them.

https://www.ebay.com/itm/B3-Color-1-8-TFT-ESR-Meter-Transistor-Resistor-Diode-Triode-Capacitor-Tester/192636462059?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649
Click to expand...

Also look into this one. Seems like I’ve looked at them before. Thanks.


Martian said:
Those transistor checkers are good for basic tests... like does it look like a transistor, etc.
Also for the unknowns - what does it think this part is..

Not sure why you can't get a good portable tester anymore.
Probably because it can't fit in a pocket.
I still have several made by Leader like the LTC-906 and 906A that I use all the time.
I have a super cricket someplace - also a fantastic tester.
If I want to know if it really works I use a Tek 577 or one of the Leader or Sencore transistor testers.
They can actually stress the device, which the Atlas cannot.
Click to expand...

That’s probably more along the lines of what I need. I spend too much time like it is with this mess, repairs are taking too long. An in circuit tester for transistors and capacitors are definitely a must have, which I don’t have. Knowledge and experience also goes a long way too...
 
I believe this thing doesn’t always give a clear “pass” or “fail”. Somebody correct me if I’m wrong here but I believe since it test as a much lower voltage than what’s listed on the data sheet for a given device, you have to do some math. A rough example, if a transistor is tested at 12v and gives a gain of 25 and the tester is only testing at 6v and gives a gain of 12, its most likely good. Am I correct in this assumption?

Of course those numbers aren’t right for the tester, that’s just an example. I’ve seen it show transistors as diode junctions when they were bad instead of saying the part was faulty. I’ve seen what I thought was a bad transistor because of a low gain number when I believe it was simply because the test voltage was much lower than what was listed on the data sheet. Again, am I right in this assumption?

The Pro version of this tester gives more options and the ability to connect it to a computer but I don’t think it makes it better. Not in the sense that it shows pass and fail any more clear than what this version does.

I can give a better example if needed. Does anyone else here use this tester? I’m kinda annoyed by having to do math to try to figure out if the part is actually in spec or not. Is there a tester that clearly gives a complete fail or pass that I’m not aware of? An in-circuit tester would be even better, I’ve seen a lot of older testers on eBay but not sure which one would work best.
 
To me "Hfe" is a frequency component - not necessarily a "cast in stone" DC value - it's a gain factor. So if it checks at say 3V - the Hfe should be the same for it at 12V - it's the frequency sweep component of the tester - if it says Hfe of 12 and the part is rated for typical 25 - then the part is failed .not enough gain for the AC side of things.

Going back to another way of looking at this, you can determine if the parts all have the same gain value. Hence - part matching.

DC gain is also shown as a Hfe on these testers. Once it sorts out which lead does what - then it needs to see if the thing can actually conduct - so it "pokes" the base a small level of power to see what it does to the output across the part - it looks at how much it had to apply, to what it sees as output, and shows that as a gain value and many a time they consider Hfe a gain factor - use it for what it's worth.

Hfe I used to see (as in taught) as a Hysteresis effect. How quickly, or slowly - a reaction to a change occurs. So the quicker the changes - in semiconductors - refers to an ability for the part to operate in a wide frequency range. The quicker the part could obtain a full on value - means less skewing and slewing of an input signal (Digital or Analog - does not matter). However, in using this effect - can generate a signal change of greater amplitude than that which can be compensated for - asymmetry - non-linear functions.

There is another part of that tester you're not using, that is the B-E voltage drop reading.

If you think you have bad parts and you want to check for them being - Good or Bad - then not just Hfe, but B-E needs to be reviewed too. That can say tons about the condition of the part. Anything below 0.7V is considered ok, between 0.7 to 0.55V is ok, while less than 0.5 its TOASTED (short - it should tell you that though)...But, you can at least determine if the B-E junction failed and it indicates how you need to approach the circuit it was used in to fix it.
 
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Well I was just using the gain as an example, I’m not sure that this thing is showing what the B-E is, maybe I’m overlooking it or not understanding what I’m looking at?

I guess the odd thing I’ve seen with it that makes me scratch my head is excessive low gain readings. I’d assume that definitely meant a bad part but in the circuit, it seems to work correctly. Like a final transistor for example, the gain would show way low compared to the data sheet yet the radio would be showing the correct output. That’s what got me thinking you had to do some math to get the correct figure.

I’ll look it back over and see if I’m missing what you’re talking about, I’m pretty sure you know more about it than I do so I’m probably missing something.
 
Well, the only math is comparisons.

Thumb thru the menu...

Grab the datasheet and compare the results - you have to use the unit and verify it does what is supposed to.

The interesting "part" you mentioned about the Final and Driver are its' Hfe Gain figures.

Remember that - because Final and Driver can have a LOT more gain only that tester is going to show baseline figure not always the correct Gain values - so the other parts of the menu need to be considered.

Again, this is based upon a field tester, and it's own limitations - in dealing with a wide range of parts. The older Discrete are "analog" to it so it thinks they are slower than MOSFET and I can see where you have a difference of opinion of their work - then what they may think of it.

I went looking around at a lot of different sites in the Amazonian and e-Bore world and there is a WIDE and I do mean WIDE range of interpretations of how that device helps others...

To some it's a SINNER - to others Its' a SAINT and to you...well - it's posting really low numbers...
 
I think some of it is my lack of words to explain what I’m seeing and what I’m questioning. When I have time I’ll go through a few devices and I’ll post exactly what I’m seeing. Maybe then it’ll be more clear and possibly I have a faulty tester, maybe I have a faulty interpretation.
 
Paralysis thru analysis.
Too much noise...

A comparison of tools. Test subject is a 2SC1969 (original NOS)
DCA55 = 48
RCA WT-501A = ~46
Super Cricket = ~47
Some Chinese thing I have with a ZIF socket = 47
Tek 370 Curve tracer (numbers crunched) = 47

All tested with < 5mA

Most of these tools were designed to do quick cursory tests, not write datasheets or to do performance analysis.
They are tools, not decision makers.
If you are trying to do repairs the DCA55 is fine as a tool along with a diode test.

In what's left of the consumer repair industry time really is money. Don't get bogged down in the semantics.
 
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The DCA55 read just a touch higher but that's within a margin of error.
We really don't care about such small differences.

It's good enough and close enough.
The only thing it does not do is more than a few mA unlike the RCA or the Tek 370.
The RCA or the Tek are where I go if I really question a device because I can run the RCA up to 1A and the Tek to several amps.
High enough that you would need to heatsink the device.
Now, 370s are out there for 5-10k but the RCA can be had for <$50
There is one on the flea right now for a damn good price, in fact.
 

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