Testing & Replacing Output Transistors - SAE Mark III Amplifier - Part 1b

[@funeralparties]

Thank you so much for this video and explanation. To clarify the glitch in the video (many others commented on it as well).. this is the CORRECT lead positioning: When testing NPNs, red lead is on the Base pin and black lead on the Emitter pin When testing PNPs, black lead on Base pin and red lead on Emitter pin Op's leads were reversed on the analogue Simpson, so it is confusing to watch at first.

[@grahamluscombememories9897]

You are my favorite KZbin tutor for electronics

[@g.fortin3228]

Think I'll be pulling out my analog meter and finding room on the bench for it ! thanks for the schooling Tony !!

[@yaminhameed1524]

I'd like to share an experience I had and hopefully get your view on it - so I was working on a fender bass amp which had parallel output transistors. I went through them with my DMM (in diode mode) all the transistors checked out ok. Powered it on, 'boom' fuse blows. So I desoldered the whole lot and turns out one NPN transistors was shorted. Replaced the shorted transistor and checked all the other transistors, powered on, 'boom' fuse flows (I bypassed my current limiter bulb). Anyway I discussed this with one of the veteran tech here and he said that I should measure them using an analog meter - similar to what you have showed. Apparently there would be an 'acceptable' range of resistance between C & E (ideally it there should be no reading). So I followed his instructions and measured all the transistors using my analog meter and all the transistors showed some resistance between C & E. I compared the results with brand new transistors and the new ones does not show any resistance between C & E. He calls it leakage current. I was wondering if there was such a thing as an 'acceptable range'. If so what would that be? Could that be an indication whether a transistor needs replacing or not. Thanks and I really do enjoy your content. p.s- I replaced all the output transistors of the amp and it's back in working order.

[@jimmissenda6590]

Nice to see some old school semiconductor testing. Simpson 260s are still usable in 2020.

[@andydelle4509]

I started out in a high school senior credit work study program at a local TV station in 1977. The engineering shop where I worked had a Simpson 260 and a brand spanking new Simpson (1977 expensive) digital meter. The Chief Engineer would not let me use it much. I was forced to use the old 260! Looking back and soon after a formal EE program, I am very glad he did that! Far too many graduate EE's today have no clue as to these basic principles. It's all HDL, MatLab, and Python programming.

[@김황수-t8g]

excellent explanation of transistors

[@andydelle4509]

I agree Tony. When you have that much collateral damage to a power amplifier, especially a vintage unit, replace all transistors in that sub circuit section no matter which still check good. Some will strongly disagree saying that transistors are either good or bad, no in-between. I agree from a strict engineering point of view, but how do you measure stress the junction may have been subjected too? Also even crude matching such as buying from the same lot has it's advantages especially when mixing 1970s parts with 2000s era parts.

[@1pcfred]

I just use an AVR transistor tester. It doesn't matter how you hook it up the tester figures it out. Those things are brilliant.

[@gregnewberry4813]

The leads on my older RS Micronta meter are reversed as well. In ohm mode the positive is negative. Sure threw me off in the first half of the video. Great video, Thanks Tony!

[@spyder8986]

Thank you for the video, I have full boxes of these transistors I got at a tag sale for like 20$ .your the first one I could find on how to test these High hat transistors I guess there called. Thanks.

[@mrmaxgain]

You have the 260 on -DC, so the applied polarity is reversed. When the black lead is attached to Cathode of diode and the red lead to the Anode, the meter should show lower resistance.

[@Bob_V]

Glad you got that, I did Too :)

[@dinosaursr]

This was very helpful. I’m trying to source a power amp failure on a Marantz 2230. Thanks!

[@Gerrit-Max]

It's always advisable to replace all end stage transistors instead of just replacing the dead ones. That way the amp will stay symetrical on both channels. I had to do the same thing when I initially bought my Pioneer SA7500 in the early 90's. One channel was dead so I just replaced all end stage transistors.

[@1pcfred]

You can pull two transistors off the line while they're being manufactured and they're not going to be matched.

[@johnnytacokleinschmidt515]

At 4:00 minutes I've always thought draw the smiley face and "BE" happy! Also the old analog meters commonly have opposite polarity on the test leads. You may cover that further along in the video. Thanks

[@adielawson6854]

This is old-school testing! I've got my dad's old Simpson meter like that.

[@circuitmonkey6653]

Trap for young players: While Tony is testing for direct shorts to immediately discern good transistors from bad, one that tests "good" in this fashion may be "leaky" and not function correctly in circuit. This can range from improperly functioning to flat inoperable, generally becoming worse as the transistor power increases towards the breakdown voltage. Just a little food for thought if your circuit is having an issue and testing indicated a "good" transistor.

[@josepeixoto3384]

How do you test a transistor for that,for a leaky transistor?

[@adamwolfram6126]

Great video, Tony!

[@dalemoorman664]

Really nice video, watched a ton of them, But you’re the first that actually showed testing a bad transistor so you could see how the meter reads it. I’m trying to test germanium, transistors and silicon and I’m getting weird results. This video will help with that. I built a simple gain testing circuit. I am really struggling to get consistent results between germanium and silicon transistors. Any thoughts on why I might be getting such mixed results?

[@johnnytoobad7785]

Lucky to find comp. pairs in TO3 package today..

[@dirtydon8661]

Wait a second here, PNP you put negative on base and NPN put positive on base. Am I missing something due to lack of sleep?

[@Gamma67]

Yeah, that's what I was thinking. The polarity of the probes are reversed.

[@russellhltn1396]

Some meters are "reversed polarity" when in ohms test. If you take a simple voltmeter, and then add a battery to make it a ohm meter, the voltage on the probes are reversed. In a analog meter, you'd have to add switching (and complexity) to make it match. Digital meters read both both polarities, so you can insert the battery "backwards" and hide the sign to make the probe polarity match. So, generally analogs will be reversed and digital true, but there's probably examples out there that break that generalization. Bottom line, you have to know your meter.

[@xraytonyb]

It has to do with the simpson 260. The +DC and -DC settings on the selector knob will actually reverse the polarity of the voltage in ohms mode! I think I had the meter set to -DC, which would have placed negative voltage on the red probe. I will have to clarify that on a future video. Thanks for bringing that up!

[@larryshaver3568]

I'm with you re: analog meters they don't tend to give confusing information

[@russellhueners8499]

Nice PSM6 there matey!

[@RGD-Audio-Repairs]

Its a shame the To-3 transistors are so darn expensive! Im currently repairing a Peavey power amp, with 24 transistors in total... 98% of them are bad, according to following your video.. :( Thats alot of money to replace them :(

[@katiecucumber]

Its quite strange that they are, other than better heat dissipation, the plastic cased ones do the same job. Considering that the diamond packaged TR'S are harder to mount having to use more insulator pieces, it doesn't make much sense. Okay they look nicer, but they are quite impractical for ease of mounting. I think it could be because of the older Ge types are no longer made which is much more understandable why these cost more. Its an old con. Perhaps the new ones are harder to make.

[@gkuzic21]

Could you explane on-board transistor testing,do we need mowe them from the board to get correct readings..

[@williamsquires3070]

(@2:46) - Whoa there, horsey! You’ve got the test leads reversed at the meter (or the meter is wired incorrectly inside). You’re putting the red (+) lead on the cathode of the diode (Emitter or Collector of an NPN transistor), and the black lead (-) on the anode (Base of an NPN transistor.) You should get no reading (infinite resistance) here, but the meter is showing conductivity here. Likewise, when you put the red lead on the anode (Base), and the black lead on the cathode (Emitter or Collector), you should get conductivity, but the meter needle doesn’t move. Either that, or your diodes are labeled incorrectly w/respect to the banded end. You’ve got the same problem with your PNP analogue.

[@xraytonyb]

Interesting fact about the Simpson 260 - When the range knob is set to ohms and the selector knob is set to +DC, there will be +positive at the red probe, with respect to the black probe. If the range is set to ohms and the selector is set to -DC, then there will be negative voltage on the red probe, with respect to the black probe. If you are set to ohms and the selector is set to continuity, there will be +9 volts (the 9 volt battery) at the red probe. For checking ohms, it doesn't matter, but when checking diodes, it does. I would have to check back on the video, but I think I may have had the selector set to -DC. Thanks for catching that!

[@giuseppebeppe_tv8257]

@@xraytonyb the selector was in -DC position ....so you had the positive on the black probe....

[@funeralparties]

@@giuseppebeppe_tv8257 later in the video the digital probes are correct, that's what I used as reference. When he first tests the NPN with the Simpson, I became confused.

[@RapperBC]

@@xraytonyb @William Squires, this caused me much confusion until I saw that Tony has his meter switch on " DC - ". As Tony points out, that Simpson's red probe is actually delivering negative voltage to the cathode of those diodes. I have an old Micronta analog meter I keep around for low-impedance voltage testing, and the red probe on that Micronta delivers negative voltage when on the "Ohms" ranges, and does so by design. It does the meter switching automatically, however, as the meter has no " DC - " setting to invert the meter's polarity.

[@wirstinson]

doing the same tests in my workshop with a simpson 260 right now

[@HillsWorkbench]

Use the Rx1 mode for the junction tests, highest range to check E-C.

[@bigmedge]

Is it acceptable to test the transistors in-circuit ??

[@jdmccorful]

Great session, you're quite the instructor. I really like the 260 method, thanks .

[@jonka1]

In no way do I wish to pour cold water on your demonstration of transistor testing, but recently I had a faulty transistor in a scope and it tested good as two diodes and also good on an ebay tester. I couldn't fix the circuit so decided to replace the transistors one by one and this particular one proved to be the culprit. It may be the voltages were not high enough in test conditions. Do you ever come across this situation in your work Tony?

[@miketaylor803]

had exactly the same thing in a 75+75W MOSFET amp - there was a BC182 that tested on a PEAK DCA 75 as TWO diodes but I knew it was the culprit - changing it and the circuit worked perfectly . The PEAK DCA75 has tested a couple of damaged transistors as two diodes - but always tests working transistors as transistors.

[@xraytonyb]

Good question! The test you saw me demonstrate with the VOM is best for testing output/power transistors, as their common failure mode is to either go short circuit or open. Small signal transistors generally fail through drift, "pop" noise, static, etc. These types of failures are very difficult to troubleshoot out of circuit, even with those little testers. If you check out some of my past videos, I show how you can connect a voltmeter to the transistor and test for voltage drift. Any type of test that doesn't apply a typical operating voltage/current won't show this type of failure. If a small transistor shorts, it will often be current limited by the resistors in the circuit and won't cause much collateral damage. A power transistor, however, will take out power supplies, circuit traces, etc. when they short. That is why I test them in this manner (with a VOM). Thanks for the comment!

[@jonka1]

@@xraytonyb Thanks for your reply Tony.

[@caicaraskiki]

@@xraytonybthanks for the nice video. I'm looking for a video on collateral damage, and how to find the extent thereof. I'm a beginner on this stuff, and so far I have a bad power capacitor and two out of four bad power transistors. Both on the same channel. The receiver only works on one channel. The other one blew out the fuses. I don't want to replace the fuses and cause further damage. But I'm curious to know what kind of other small transistors, diodes, resistors, and capacitors could have been taken out at the same time. I would hate my new found skills to be for naught by simply replacing the known transistors and power capacitor. Just to blow them again. Any points in the right direction would be greatly appreciated. Just a dumb lawyer here.

[@gavinveilleux9028]

Hey I don’t know anything about any of this, and I came here with a problem. My Behringer PA system just lights up and turns off over and over. Tricky to get it to turn on. What should I do?

[@j.dragon651]

Sounds like a protection circuit.

[@gabrielguadarrama8701]

I always use the collector as reference pnp red probe on collector. Npn black probe on collector. Am I doing something wrong. I have a nice rca 27v analog meter that works great for testing semiconductors and capacitors. Merry Christmas Ace

[@RapperBC]

Gabriel, this caused me much confusion until I saw that Tony has his meter switch on " DC - ". that Simpson's red probe is actually delivering negative voltage to the cathode of those diodes.

[@johnnytacokleinschmidt515]

@@RapperBC You're right. Many older analog meters have polarity opposite of what the probe colors suggest.

[@Kobafied]

The polarity of the probes is controlled by a switch on the meter. The video is confusing to anyone who doesn't notice that Tony has the polarity on his probes reversed. In this video, Red = negative and Black = positive due to the position of the switch on the meter. @@johnnytacokleinschmidt515

[@johnnytacokleinschmidt515]

@@Kobafied only for DC+ and DC- I don't think that applies to ohmmeter function.

[@raiderx7410]

anybody know what this amp cost new? just curious.

[@alcatel1s508]

Thx QT a Flair on tsop.. 's IR.capture

[@EmilioGarcia-fr5po]

What amp was that please

[@ruudmobile6726]

Calibration due 2-1-20??? LOL... Merry Christmas Tony!

[@xraytonyb]

The meter movement began sticking a couple of years ago. I contacted simpson to see if i could still buy one and they told me to send it in and they would evaluate it for no charge. I sent it in, thinking they were going to quote a crazy price for the repair. A week later, i got an email stating that they replaced the movement and calibrated the meter..... no charge! The even paid the shipping costs to return it to me! Simpson rocks!

[@ruudmobile6726]

@@xraytonyb Some of these truly awesome brands still exist... there is still hope for mankind I guess.The meter will now hold a sweet place in your collection I trust...

[@randywl8925]

​@@xraytonybI know this is an old one but I just read your comment about that company and it's nice to know those kind of people still exist.

[@hasanalmeer6242]

Nice multimeter

[@boxingday11]

Thanks sir.

[@bobbyy8711]

thank you..

[@alcatel1s508]

Thx qSL CW..

[@HipocratesAG]

260 FTW!!!

[@ronbradshaw7404]

Guys, silly question: i always wondered what PNP and NPN means?

[@ronbradshaw7404]

@RebelDeuce Oks! thanks!

[@harryconover289]

I prefer the Simpson 260 I like the move to and reliability you have 12 to3 on your heatsink but only 1 and 1 down on the circuit? So now thing to Match

[@Bob_V]

I love how these people want to teach with a bright shiny new meter and have no idea what the hell they are talking about. I have been doing electronics for 40+ years and what he is telling you is just flat out WRONG !!!!!

[@livens100]

Please elaborate

[@hestheMaster]

Collateral damage due to very weak capacitors and poor heat dissipation design. Replace them all. Love those Peak testers!

[@pulesjet]

Cut my teeth on a Simpson like that. Wish I had one today.

[@pulesjet]

@RebelDeuce 79-90 USAF

[@pulesjet]

@RebelDeuce 307X0

[@russellhueners8499]

@@pulesjet 1974-78 307X0, we walk on water

[@pulesjet]

@@russellhueners8499 Some times we thought so.

[@alcatel1s508]

Surf-sail

[@johnsweda2999]

Are my comments showing up? Somebody let me know

[@DanielMelendrezPhD]

Yup

[@bobbybiggs4348]

Correct

[@HipocratesAG]

No, they don't. :P

[@johnsweda2999]

@RebelDeuce that's what I thought he's blocked me

[@johnsweda2999]

@Mike Eastridge I'm over here