Cheap TV amplifier teardown - Page 1
Forum section: electronics / general

author: reagle
author_rank: Unknown
timestamp: May 11, 2013, 04:11:06 pm
content: After a few years of using this amp, I noticed it started getting toasty. So I promptly tore it apart, and it appears just in time.On a positive note, they did put a fuse into a transformer legDoes anybody know what are they doing with these disk-like things they insert and solder through the slots in the board? Custom made caps of some sort?Oh, and I bet the bent coils (like L5)are set so precisely with the correct tongue angle

author: SeanB
author_rank: Super Contributor
timestamp: May 11, 2013, 04:41:25 pm
content: Those are ceramic capacitors, leadless so they have a very low self inductance. They are also available in a trapezoidal shape that are appropriately called tombstone capacitors. I see they have changed to SMT RF transistors, normally they use a TO92 packaged one, or a small round pill package with 3 leads. Normally these fail because of lightning, or those cheap OHL electrolytics in the power supply section going basically open circuit, as the amplifier will work with about 5V of 100/120Hz ripple on the supply rails with almost no visible effect on the signal.

author: reagle
author_rank: Unknown
timestamp: May 11, 2013, 05:05:06 pm
content: So I take it this one is not the worst one you've seen?

author: SeanB
author_rank: Super Contributor
timestamp: May 11, 2013, 05:17:50 pm
content: Pretty much par for the course, and at least made with proper solder joints. Could have been a lot worse, but it gave you years of service, and with a little work could have done decades more. About average for the cheap set back amplifier, always room for improvement, but being mass made by hand in some Chines sweatshop it is not bad.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 11, 2013, 08:07:18 pm
content: I have a good quality coaxial amplifier, an Electroline EDA 2100. It only does a "modest" 15dB but I'm pretty sure it can really do that. (You could label a cheap amp 100dB and the average consumer wouldn't know that it really only does 9dB...) Unfortunately, it appears to be potted so no teardown. I would expect a quality double sided board, with a GaAs or SiGe LNA, and a fair amount of ESD protection built in.

author: peter.mitchell
author_rank: Super Contributor
timestamp: May 13, 2013, 07:36:59 am
content: Seems like someone "forgot" the other parts of the full wave rectifierThough that is to be expected...I am genuinely curious as to why the board is so big though, would it be for ease of unskilled manufacture or just because "bob said this'll work" "yeah, she'll be right mate"

author: SeanB
author_rank: Super Contributor
timestamp: May 13, 2013, 06:02:12 pm
content: With a power consumption of 20mA or so a half wave works well enough. Transformer losses are more than the circuit uses in most cases, they generally use 5W of power with 4W being lost in the transformer. A big board is used so as to have separation between input and output by large low inductance ground planes. If you make the board small you need to add shielding between stages soldered to the ground plane in multiple places. Cheaper to make the board bigger so that it does not oscillate.