What are these boombox components for? - Page 1
Forum section: electronics / beginners

author: lpc32
author_rank: Frequent Contributor
timestamp: December 09, 2014, 12:37:50 am
content: Can someone shed light on what these parts are for? I'm guessing it's all standard in old tape/radio/amp circuits.What exactly do these adjust in the tape deck?There are multiple of these, color-coded (blue below). What might they be for?What type of capacitors (I presume) are the semi-transparent ones?

author: poot36
author_rank: Frequent Contributor
timestamp: December 09, 2014, 01:20:26 am
content: The pots are for adjusting the recording or playback volume levels to the tape head based on what the the recording or playback meter is showing level wise. If you can find the service manual for the boombox it will tell you how to adjust them for optimal sound level input and output. You will probably need a oscilloscope or a good quality multimeter to do the adjustment. The second picture is of a tunable frequency transformer for the am and fm radio reception (technical terms IF (intermediate frequency) and RF (radio frequency)) transformers. I think that the caps are tantalum but I could be wrong.

author: TSL
author_rank: Regular Contributor
timestamp: December 09, 2014, 01:34:32 am
content: The colour coded coils indicate what part of the IF chain they are in, although blue doesn't come to mind as an IF nor does it show up in a common table...http://www.electronics-tutorials.com/filters/if-amplifier-transformers.htmWe'd have to see more of the board to get an idea of where that inductor figures in grand scheme of things.The capacitors are polystyrene, eg...http://www.hificollective.co.uk/components/polystyrene.htmlregardsTim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 09, 2014, 01:36:11 am
content: Yes and yes. More specifically, the RF/IF transformer apparently is coded "64" or "46" (yellow and blue, from the resistor color codes), which....probably doesn't mean anything at all. You'd have to look them up in the manufacturer's tables to be sure... good luck on that. They're used for tuning the radio signals, so are very critical on setting, hence why they are adjustable.There may also be a crystal or ceramic filter somewhere (a two or three pin component, in a molded orange box, or a dipped wafer looking somewhat like a ceramic capacitor, but oddly shaped), which is used for final tuning, selecting just the frequency of interest and nothing else.The 'clear' capacitors are polystyrene: these were used for their low loss and high stability. Polypropylene is a suitable substitute, not quite as good but easy to find. C0G ceramic (especially in SMT chips) is an excellent alternative.The green dipped caps, of course, are most likely polyester, which is a good general purpose cap, unremarkable in loss or stability, not something you'd use for tuning a radio receiver, but still suitable for uncritical things like time delays or audio filters. Polypropylene is also available in that style, so it could be either, but polyester is more likely.Tim

author: lpc32
author_rank: Frequent Contributor
timestamp: December 09, 2014, 08:47:56 pm
content: Thanks.The specific meaning of blue doesn't matter, I was just wondering in general.Would polystyrene caps only be present in fancy gear? This boombox is rather plain. How do the advantages of polystyrene manifest in this use?Speaking of the green caps, are there any official packaging standards to help identify capacitor types?

author: Zero999
author_rank: Super Contributor
timestamp: December 09, 2014, 08:53:26 pm
content: Polystyrene capacitors have a fairly close tolerance and high stability.They're not so common in new equipment.Here's a link to the marking codes used:http://wiki.xtronics.com/index.php/Capacitor_Codes

author: Yansi
author_rank: Super Contributor
timestamp: December 09, 2014, 09:01:41 pm
content: The "RF" tank is not exactly RF, it is probably part of an LC oscillator for erasing head.Green epoxy coated caps has only "china standards", their footprints are a bit odd, like 6mm leg to leg distace, etc. You can buy them from china (ebay, aliexpress,...) very cheap. These are "good enough" for some basic audio or analog signal conditioning circouits. But I recommend to use industry standard film capacitors, lika WIMA, ARCOTRONICS, VISHAY, PHILIPS... The will not cost you much more than those crappy green ones, which are being made expecially for lower cost devices.

author: Zero999
author_rank: Super Contributor
timestamp: December 09, 2014, 09:37:01 pm
content: Those green capacitors aren't that bad. They're much more linear than most ceramic disc capacitors.I think those green cylinders with red dots on are inductors.

author: lpc32
author_rank: Frequent Contributor
timestamp: December 09, 2014, 09:49:32 pm
content: By "packaging standards" I mean package color/shape, not letter codes. Ceramic thruholes tend to be round matte brown. Wet electrolytics: plastic covered metal cans. PP/PET film: glossy green chiclets? Etc."China standards"I don't know about nowadays, but this boombox was made in Korea in the 80s, and it includes Panasonic potentiometers, so the rest are probably also decent components.

author: Yansi
author_rank: Super Contributor
timestamp: December 10, 2014, 12:55:32 am
content: By china I've thought about Asia production. (for us, Europeans, everything from east comes from china :-) ) But wait, I've just spotted a nippon electrolytic. Thats better now, so, a better asian productQuote from: Hero999 on December 09, 2014, 09:37:01 pmThats without a doubt. I've only noted that there are even better caps today. But to be exact, C0G (NP0) ceramic caps are also well linear and stable.These green epoxy coated are mylar (polyester), if I got it right. Quite good. I also have a whole bunch of those in a drawer.Yes, that green with red dots in your photo are dumbbell inductors (because the ferrite core looks like a dumbbell). Those dots mark the value. This marking looks odd, but standard epoxy (or something) potted inductors are labeld by two color spots on the top ant the multiplier is marked on the side of the inductor. The decoding process is the same as for color bands on a resistor. Tha base order is a microhenry (uH), so if you see an inductor with red and violet mark on top and black on the side, that gives you 270 and that equals 27*10^0 = 27uH.aaaaargh.. hard to find a photo of the dot-marked inductor. Fail. So I've just taken a snapshot of my collection of those:Same color decoding rule applies to these inductors (this is a 47uH one):http://img4.wikia.nocookie.net/__cb20090113231816/howto/en/images/7/74/Axial-inductor-on-PCB-board.jpgInductors are also coded by numbers printed on them, same numbers as from the color decoding method. And usually there is a letter at the end of the number, which marks the possible deviation. So if you see an inductor with 331K written on top, that will be 330uH and "K" stands for I think 10%. The letters are also standardised coding.Note: Be careful when salvaging through hole components from modern boards. Not only resistors (usually light blue or gray like) and inductors (usually light green) are being made in packages like 0207 or 0204. Also ceramic capacitors (usualy pink or slight redish color tone) are being made today in these through hole packages. You can sure yourself by the silkscreen marking.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 10, 2014, 03:21:45 am
content: I don't think that was the picture you were looking for...

author: Yansi
author_rank: Super Contributor
timestamp: December 10, 2014, 08:24:00 am
content: why do you think so?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 10, 2014, 08:53:56 am
content: You may have a different image cached than what others are seeing...Here's the Tinypic link,http://tinypic.com/view.php?pic=j0lky1&s=8Tim

author: Yansi
author_rank: Super Contributor
timestamp: December 10, 2014, 09:17:39 am
content: That seems like some american problemLink is OKay, the image here is right. I am now 20km away from home where I uploaded the image yesterday, another computer). So not a caching problem, but server side problem. But thanx for info, I will not use tinypic imagehosting again here.So here's the image as an attachement. Bloody tinypic...