KMART 06-31-62 AM/FM Radio #2 - 1 Step Forward, 2 Steps Back - Part 02

KMART 06-31-62 AM/FM Radio #2 - 1 Step Forward, 2 Steps Back - Part 02. Be sure to like, subscribe, comment!
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VEG
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[@westelaudio943]

Jack, "regular" hum is always line frequency x2, with a full bridge rectifier that is, which is turning hollers into peaks, if you will. However, ~100 cycles, and obviously slightly drifting all the time, can never be mains hum. It's an internally generated oscillation which is likely in the preamp section. If it is not a bypass cap problem it might even be a bad switch contact, solder joint or something. The sound should also be present on batteries (DC).

[@VintageElectronicsGeek]

WA - thank you for your input....you really need to start your channel, you'd be a big hit! :) Without those two transistor's in there, the radio is not working...trying to find replacements now...if problem is still there, will look at others you suggested. ~Jack, VEG

[@umajunkcollector]

this week, i got a Sangean AM/FM radio, simukar in size, at Sal Army for 5$ and it works great. At first, i regreted buying it, nothing good on a radio to lusten to now days. but i actually enjoy air checks and reports, and some of the DJs.. i used to listen to the GE you fixed up for me at night, i keep it handy in my headboard for late night DXing, it actually out performs the Sangean. same complaint, nothing good to listen to on AM these fays. .

[@VintageElectronicsGeek]

Wow, that's a big radio! But I would imagine it works well! That is an awesome price, ida bought it as well! Wow, that's awesome that the GE kicks butt, especially over the Sangean, I was going to suggest you do a shootout video between the two. That GE was / is a very impressive radio...I think it may have outperformed my Sony's as well. ~Jack, VEG

[@LarryDeSilva64]

Yes run away oscillation is a real problem. I'm with Doug though just switch to using dc battery power and that should eliminate the ac hum. It would be just one more troubleshooting idea. Then you can hook a scope to it and see what is spiking. I mean transistor do short out so it would not be unheard of the replace them. Ok one eyed Jack I have the same problem the DMV has got me listed as a one eyed driver because I can not focus with my right eye on anything. But my other left eye is correctible to 20/20 thank God. Monday I go in for my Chemo Therapy orientation to see all that they will be doing to me.

[@VintageElectronicsGeek]

Larry - I hope your health gets better you are to young my friend! My post on your last video disappeared?? Once I get the radio back up and running I will try it on batteries and not DC power supply and see what happens. It sux a) having eye issues b) getting older, but hey at least our generation are not cowards nor confused at who and what we are (mostly)! ~Jack, VEG

[@LarryDeSilva64]

@@VintageElectronicsGeek you know my dad made it to79 and died of Lung cancer my mom died at 87 from Lewy Body Dimentia. The average life span in our family is 76 I figure I will be lucky if I get that far.

[@raymondward5629]

Life is short-you get what you pay for. The blue dumpster is the solution

[@hestheMaster]

I had to look back at the shot of the transistor in question. Probably MPS9411A. 15:53 in video. Look it up in an old 18th edition of ECG cross ref. parts. Got a discontinued part number ECG 299 with one exception. The MPS9411A1 which came back to ECG 287. But that is an NPN high voltage general purpose amp and way overkill. I sense this a Panasonic made radio. I don't know much about these early transistor radios but those transistor kits are of low quality and have low quality control. 2N3904 may be a better substitute than a 2N2222. Check them first! Thank goodness ( or just plain luck ) that you have a seocnd radio to compare it to!

[@VintageElectronicsGeek]

HTM - Wow, thank you very much for taking your time to research and help me out, I very much appreciate it! After watching this video, I think I may have installed one of the 2222 incorrectly and that maybe(?) the reason it didn't fire back I need to pull it out, since I'm there I will try the 2222 just for the heck of it, however will swap and put in 2N3904's. Interesting thought on the maker, yes low quality indeed, but its from my younger days, special time, special memories that the radio offers. You know what they say mainly about guys...the older you get, the more you try to buy your youth...and that's true, I'm trying to get the band back together! ~Jack, VEG

[@JCWise-sf9ww]

I bet the Problem was battery fluid dried on to pc board in the area of the two audio transformer making a resistive feedback path that was making the push-pull transistors to oscillate like a muiltivbrator. I had a transistor pocket radio that had battery fluid problem around the output transistors. Had to scrap and wash of the pc board, then the radio worked like a champ. Replacement transistors can have EBC different arrangement like ECB. Most likely the original output transistors were ok. I don't see why you could not just use the 2N2222' or 2N3902's, I found a data sheet for MPS9411A and it's essentially the same as the two mention.

[@umajunkcollector]

hi javk, um guessing a signal from outer space of ET's. perhaps there will be an invasion from outer space!

[@VintageElectronicsGeek]

Invasion Of The Hot Female Body Snatchers / War Of The World! ~Jack, VEG

[@DERB_Seymour_Indiana]

Hey Jack, I started writing my comment several times and each time I decided it wasn't fair to you and the lovely Mrs. VEG. I think instead I should tell you that you need a much more logical approach to the problem. To be honest I don't remember part 1 of this series so I don't recall if you tried the radio using batteries instead of AC. That would eliminate the possibility of this being related to the line voltage. In other words, if you run the radio on battery voltage and the problem goes away, that means the problem is related to the AC section of the power supply. If the problem is the same on battery then it means it the problem is not coming from the line, but it is coming from within the circuitry of the unit itself. Once you have established this you can begin logical deduction of the actual problem using the scope to find out where in the circuit the oscillation occurs and where it doesn't occur. I believe it is present when you turn the unit on, but very difficult to see on the trace as it is so small. Check to see if increasing the scope sensitivity will show that or not. The fact that the oscillation signal gets larger when you increase the volume means the problem is before the volume control. An oscillation in a later stage of the audio section would be present no matter what the setting of the volume control is. I hope this helps. :)

[@VintageElectronicsGeek]

Thanks Doug! I did test the radio on a DC power supply, however it wasn't until reading your post that it reminded me that a EE once told me that DC power supplies could also cause issues that batteries would be the best. So, once I get the radio back into a working state, if I still have oscillating issues, I will try it on batteries. Thank you very much for your guidance! ~Jack, VEG