Component ID help please? (Here we go again!)

[starhawk]

Bought a 1985 Zenith BT044S -- Bravo Tango Zero Four Four Sierra -- off eBay, back in late May... had to set it aside because IRL Drama just had a chance to power it on aaaaand...

Yep, magic smoke listing said "TV powers on and has sound". Well! I certainly made a sound when I saw the smoke coming out of the vent... I don't think that counts, though. /sigh

I only powered it off the external barrel jack. I don't have the four "C" cells it requires to run it on battery power, and although I've a 6v lantern battery I've not got alligator (int'l: crocodile clip) leads, and I'm not about to put 2/3 of an amp at 6vDC through a couple wire twists 'round the battery springs!

Alas, although I see which component has failed, and I can describe it well -- I can find no schematics, nor can I properly identify the component itself. It is marked Q502, and is a four-pin part. It looks like an early SOT223 style package. It has two markings, one at either end, each two characters long -- "GP" at one end, "56" at the other. I can verify that there is no component in that spot on the other side, and that there is a scorch mark on the other side as well as on the "X-Radiation Warning" paper on the inside of the lid (!!).

My smartphone is at a repair shop until tomorrow (Wednesday) sometime, having taken a momentary sojourn into the indoor birdbath wearing the wrong color bikini (lol) -- the first time I've ever managed that, and I've had a cell phone of my own since the early 2000s :-/ but I managed to dig up an old Nikon S70 digital camera which hopefully has sufficient picture quality to help here. The photo it produced is attached.

Can anyone identify this component? Even better, can anyone suggest a modern replacement?

[Nusa]

When you used the external power jack, did you notice it was 6V center negative, which is the opposite of what most modern devices use? Check whatever you were using for power to make sure it matches. If not, you know why it blew.

[starhawk]

[ 10 minute long 'bleep' to avoid FCC fine ]

Thanks, Zenith, for yet another reason to hate the fact that the "Casio pinout" barrel jack exists. /sigh

@Nusa -- OK, now that we've identified the point of failure as being caused by a PEBCAK issue, any guess as to that component and a modern replacement?

[starhawk]

PEBCAK = "Problem Exists Between Chair And Keyboard", BTW...

Anyone able to ID that component?

EDIT ~20min LATER: if it helps, the component in question is the large black block in the photo. Five pins, looks like an early 5pin SOT-223 like I said (picture one of those really awful A1117 vregs). If the markings were more definitive, I could pin it down, but I can't.

[Terry Bites]

You could always desolder it and see what kind of transistor Q602 is (or regulator) . https://www.sphere.bc.ca/download/smd-codebook.pdf

[starhawk]

@ Terry Bites -- even if it's gone all melty-smokey, as indicated quite clearly? I have one of those one-button "multi component tester" things from eBay but I really don't think this thing is gonna show up!

Did more searching... Creepy Uncle Google wants to suggest the BCP56 transistor, but of course modern marking codes are entirely different from what's on this one, and I can't find a period datasheet.

Potential alternatives I've found are as follows...
2SB757 Amplifying Power BJT from New Jersey Semi (this is a VERY old datasheet!)
BSP135 and
BSP149 "SIPMOS" Small-Signal Transistor, both from Infineon
FZT849 Power BJT from Diodes Inc
PJW4P06A-AU MOSFET from PanJit
PZTA42 HV BJT from Infineon
STN3F06 MOSFET from STMicro
and last but not least...
TSH70 Op-Amp from STMicro, which *does* have a SOT223 version

Anyone want to weigh in?

[Nusa]

Is there any reason to leave it on the board? You can't repair it without removing it, and taking it off may clarify a few things. And the board itself may need a cleanup and trace repair.

You've described it both as a sot223-4 and a sot223-5, and it might be either under that solder blob in the fuzzy picture (choose in focus over very close if you take another picture).  Assuming it's a 223 at all. Measuring the package with calipers will tell you that. If it's a 3-pin with a tab, are pin 2 and the tab connected, as is common?

Functionally, it's most likely a simple voltage regulator. If you reverse engineer the 600's part of the board between the battery and that IC, you may get a better idea. You can probably determine where the input and ground pins are, and by deduction the output pin. Once you have an idea whats where, you might even try a voltage injection to see if it works. My blind guess would be either 3.3V or 5V. Once you're reasonably sure what the part does, you can find a replacement to do it.

[starhawk]

I'm really not sure which -223 variant it is... I'd be surprised if it was a vreg, though, given the age of the TV (again, per first line of the first post, it's a 1985 job!) but I won't refuse the idea. Calipers have the measurements at 4.3mm long, 2.1mm wide. I did not attempt to measure height.

Apologies for the bad photo, as mentioned my phone took a swim on Saturday and the photo was thus taken with an old digital camera. I only got the phone back a couple hours ago. New, much better photos attached.

[Nusa]

Too small for 223 then. Pretty close to SOT-89 dimensions.

[starhawk]

Well... eBay calipers (tho BigClive did a pretty good video on how good those actually *are*) and it's had a bad day... and I'm not the most precise! +/- 0.1mm at *least* on those measurements!

OK, so what would have come in a SOT-89 in 1983-85? (Considering that, at least in my experience, it takes at least a year to get from factory to cash register... plus a good bit for design and all.)

[TurboTom]

2SD1615A?

[amyk]

2SD1615A?

I was going to suggest looking at the characteristics of Q802 if it couldn't be found, but... we have a winner!

https://www.sun-elle.com/eshopdo/refer/vid4004_16150.html
http://www.eric1688.com/product.aspx?id=351536

[starhawk]

YAAAY!!

Thank you both! Not too many on eBay, all overseas -- I've not yet checked Mouser, but I'd rather avoid them if I can simply out of the cost of shipping. I have a friend a few states over, I've sent him an email... we shall see. He does business in New Old Stock type parts like that.

[starhawk]

So while I'm waiting for my pal Will... any chance in heck I can bodge-wire in a 2SD1047 under the lid, on flyout leads? I have that one on hand. I know it's *massive* compared to the original transistor but if I can make it work, I want to do that. I can tell that it's close but I don't know enough to say it's close enough.

[starhawk]

Update! Never heard back from Will @ Little Electronics. Oh well... to answer my own question, the 2SD1047 doesn't work, but a 2SD1226M from an ancient floppy drive that was ticking me off the other day, *does*!

It's *really* unhappy tho. Hence the bodged-on heatsink... the copper schmutz all over the transistor is super-cheap CPU thermal paste. Turn your nose up if you want, it's fine on Atom CPUs from netbooks to stick computers as well as the sort of VIA trash they put in cheap thin clients (which are GREAT for low-end GrannyComps BTW) -- I save the silver stuff (not much more expensive, all of this is firmly in "buy 'x' tubes, get 'y' tubes free" territory lol) for better stuff, like Celerons and i3 gear when I can get something that good.

This is how we do things on my side of the tracks, tho it works for now, that's what matters!

All ya'll take care, a'ight?