| Electronics > Beginners |
| NAD 218 THX amplifier Repair. |
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| Yansi:
--- Quote from: mcinque on February 17, 2019, 05:59:22 pm ---If you want to win high probability of fakes and inconsistent stocks, go on ebay or aliexpress. Someone tells that ebay and aliexpress are fine and yes, you can be lucky and purchase a good stock or genuine transistors sometimes. But if you place another same order after some days, even to the same seller, you can receive a mix of different faked products because the seller's sources are not the manufacturers but other resellers that purchase from other resellers who purchase from who knows. And another important aspect is the packaging: it's completely worthless purchase genuine transistors shipped in a static plastic bag commonly used to keep anything else than electronic components. If you need genuine products, consistent stocks and protective packaging, you MUST purchase from reputable resellers: for example RS, Farnell, Distrelec, DigiKey... there is no other source other than the manufacturers. At least... if you do it to manufacture and sell a product. If you do it for hobby and don't care for reliability or esd damages... go for the cheapest seller. But you've been warned. --- End quote --- You seem to be a bit paranoid, aren't ya? You would be surprised what kind of awesome deals could be made with those chinese guys if you know them more. But from your opinion, I see you have none experience on shopping in far east or negotiating deals with the sellers directly. ESD damage of a single component is extremely y unlikely, especially with something a BIPOLAR JUNCTION transistor, think why. (Having no oxide isolated MOS is only part of it). |
| SantaClaw:
Yeah, so I de soldered the transistors on the bad channel and put them in my cheapo component tester... B1163 Test Results: BJ T-PNP #1 B=84 Uf=557mV #2 B=88 Vf=553mV #3 B=86 Vf=547mV #4 B=96 Vf=538mV D1718 Test Resilts: BJ T-NPN #5 B=117 Uf=554mV #6 B=79 Vf=561 #7 B=128 Vf=552 #8 B=128 Vf = 542mV Am I wrong, or did all of them test ok ? |
| SantaClaw:
I only have some tiny transistors left on that channel to test, could it be any of them ? One of the transistors #2, actually gave a reading as a 447 ûF cap at first, but I assume that's down to the crappy tester... btw I built it as kit so it's prolly faulty :D |
| Richard Crowley:
Those results from the transistor tests seem OK to me. What about the transistors that are driving them? Take those out and test them. How do the transistors on the good channel test by comparison? Do any of the components on the bad channel get more hot/warm than on the good channel? |
| Richard Crowley:
--- Quote from: SantaClaw on February 17, 2019, 11:20:23 pm ---I only have some tiny transistors left on that channel to test, could it be any of them ? --- End quote --- Yes. The driver transistor stage could be driving the output stage into saturation. Do you have a schematic diagram for the amp? Can you measure the voltages at key nodes on the good channel to establish what "normal" should be? Did you say that the amp operates for a short time before failing? After establishing "normal" voltages on the good channel, can you then quickly probe a few key nodes on the bad channel? That would be very helpful to drill down on the bad channel to see where it was going wrong. --- Quote ---One of the transistors #2, actually gave a reading as a 447 ûF cap at first, but I assume that's down to the crappy tester... btw I built it as kit so it's prolly faulty :D --- End quote --- It sounds more like the tester was touching only two legs of the transistor and didn't have secure contact with all three legs. |
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