Fixing stereo ampilfier - Page 1
Forum section: electronics / repair

author: stdcall
author_rank: Newbie
timestamp: October 20, 2020, 08:01:52 pm
content: Hi.I bought a stereo amplifier to be used in an arcade machine I building, The specific model is this one:https://www.aliexpress.com/item/4000326699061.html?spm=a2g0o.productlist.0.0.1f5126deU3wk56&algo_pvid=b742774a-feaa-4dab-9a27-fa90fe49d854&algo_expid=b742774a-feaa-4dab-9a27-fa90fe49d854-13&btsid=0b0a050b16032232491132617ecd74&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_When it arrived I connected it to the power with the supplied 12V power supply and saw the leds flipping, that was enough for me to ack the shipment.However when I finally connected it to the, I saw that the ampilfier doesn't amplify, I can barely hear anything out of the speakers, and only when I set the volume to it's top.After failing to get a refund/replacement for it, I decided to see what's inside and try to fix it for myself.I started with the power supply, it outputs 12V, it's ok.Then I went on and checked the 2 IC's that I saw on the PCB.RC4558 and TDA7297SA.Here's a birdseye picture of the PCB.Anyone has an idea what should I check, and possibly can be the problem ?Thanks !Ramon

author: Ahura Mazda
author_rank: Contributor
timestamp: October 20, 2020, 08:36:06 pm
content: That thing is definitely 580W, yes. Of course. Why do they call it 580W? lolWhen you turn the volume nob, is the sound clear?Can you trace the signal and whether the signals are coming to the pins 4 and 12 of the TDA7297SA? Could be very well be Chinese knock off.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: October 20, 2020, 08:49:11 pm
content: There is no heatsink on the Power Amplifier IC U1.Its intended outline is silkscreened onto thePCB.It seems you are supposed to supply your own.The Amp will overheat and shutdown in seconds without one.

author: stdcall
author_rank: Newbie
timestamp: October 20, 2020, 08:59:34 pm
content: Quote from: Audiorepair on October 20, 2020, 08:49:11 pmI temporarily removed the heat sink so I can read the part ID.It's there and will be put back soon.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: October 20, 2020, 09:21:23 pm
content: Ah, ok!the amp IC will have mute and standby pins.One of these will probably be muted or in standby.You might have to provide these signals somehow, it should be in the documentation you got with the kit if there is any.

author: ambrosia heart
author_rank: Regular Contributor
timestamp: October 21, 2020, 02:33:23 am
content: There are 2 ICs here, one op-amp and one power amp.(0)Make sure they have been supplied with proper voltage.(1)Download 50Hz wave file, playing it in android phone.(2)Connecting your android phone to stereo amp RCA input.(3)Download op-amp datasheet, finding out which pin is output.(4)measure input and output voltage with respect to ground to see if voltage is amplified.(5)Download power-amp datasheet, finding out which pin is input.(6)measure power-amp input voltage with respect to ground , comparing it with op-amp output if they are in same value(8)If they are not the in same value, check the coupling capacitor capacitance located between them.(9)measure power-amp output voltage with respect to ground to see if voltage is amplified.Never use this amp. except you are at home.The power amp IC will short and burn easily.The fuse did not burnand the IC kept burning in yellow colour.How horrible it was.If you want your house on fire,use it.I bought this cheap amp in Hong Kong in Kwun Tongplaza 3 floor in 1998and never forgot this scene.

author: Haenk
author_rank: Super Contributor
timestamp: October 21, 2020, 07:29:00 am
content: There is no reason for a fuse (well, those always help, but it is not mains powered), and this amplifier will very certainly not burn your house down, working or not.

author: stdcall
author_rank: Newbie
timestamp: October 21, 2020, 07:20:28 pm
content: Hi.Issue resolved.There was a bad soldering joint at the mute leg of the power amp. I reflowed it and now everything is working like charm. (Chinese charm)Thanks all.

author: raphaeltube
author_rank: Contributor
timestamp: October 22, 2020, 08:06:23 am
content: Quote from: ambrosia heart on October 21, 2020, 02:33:23 amI love that your list started with item zero

author: TheMG
author_rank: Frequent Contributor
timestamp: October 24, 2020, 01:18:16 am
content: Quote from: Ahura Mazda on October 20, 2020, 08:36:06 pmAssuming it is even a genuine TDA7297SA... just shy of 8W per channel at 13V supply voltage. At 12V, just a touch over 6W. That's at 1% THD.Also the Alliexpress listing is incorrect in saying the amplifier is for a 4ohm speaker load. The TDA7297SA is only spec'd for a 8ohm speaker impedance. The datasheet makes no indications that the chip will handle a 4ohm load correctly.Don't expect much out of that amplifier.

author: tooki
author_rank: Super Contributor
timestamp: October 24, 2020, 09:56:19 am
content: 580W in what, dog watts? :pAt least it says 22W on the top... in Comic Sans. 😂Anyhow, should that thing fail to meet your needs, take a look at the various TDA3000-series amps, like the TDA3226D. I’ve had good experiences with them.

author: HB9EVI
author_rank: Frequent Contributor
timestamp: October 24, 2020, 03:59:29 pm
content: the most useful part of the thingy likely is the case; at least it can serve some practical purpose. I'd not like to say that about electronics in the case. I certainly know better investments for 12 bucks

author: Audiorepair
author_rank: Frequent Contributor
timestamp: October 24, 2020, 04:27:20 pm
content: The TDA7293 has been a popular IC amp for a long time now, I have seen quite a few proper blown up.Burnt, chunks missing etc.Makes it very easy to identify the problem, though!

author: Zero999
author_rank: Super Contributor
timestamp: October 24, 2020, 05:58:17 pm
content: Quote from: stdcall on October 20, 2020, 08:01:52 pmFirstly: why couldn't you get a refund? Assuming what you've said is true and that you haven't misused it, such as connecting it to too higher voltage, or running it without the heatsink, you're legally entitled to a refund. Don't bother trying to repair it: push harder for the refund you're entitled too! Sellers shouldn't be allowed to get away with pushing crappy, faulty products!Now, if you're been refunded and allowed to keep it, or it was your fault it failed, it's most likely the power amplifier IC is faulty, but it might be better to test the op-amp first, simply because it's easier to do and cheaper to replace. If the op-amp works, then replace the power amplifier IC: it's unlikely to be the passives, so there's little point in testing them.