Teac GSA-5200 Stereo Amplifier - Page 1
Forum section: electronics / repair

author: mictas
author_rank: Regular Contributor
timestamp: December 15, 2017, 11:03:53 am
content: I have this Stereo Amplifier and it doesn't want to output any sound through the speaker output, however all the lights at the front seem to be working and it seems to respond as if I am changing the input. So this is my problem.And yes I have tested these speakers on another amplifier and they do work.I can't seem to find this Amplifier with a Google search.After taking off the top cover, I found two the two capacitors after the rectifier, in a rather sorry state, please see attached photos. Could I be correct in guessing that these could be the problem? I have taken a look around the board and can't see any other real issues, but I can't see any dry solder joins, or any other problematic looking parts. I am going to give it a soft blast of air, and clean off all the dust.I do understand I might need to replace all the capacitors, despite looking healthy.My plan is to pickup a tooth brush and once I have removed the two capacitors, give the board a clean with isopropyl alcohol and replace both capacitors with these.https://au.rs-online.com/web/p/aluminium-capacitors/7395386/Checking the voltage input to the board, it seems to have two 25 volts power input voltage. So I am going to guess 50 volts and I am going to go with a 63 volts capacitors.Capacitors in the unit 6800?F, 50 WV, 85c, CE - WI want to replace the capacitors with 6800?F, 63V, 105°CHow have I done so far?

author: Messtechniker
author_rank: Frequent Contributor
timestamp: December 15, 2017, 11:20:39 am
content: What a rotten design. Putting those power resistor close to, or touching those big honkin'capacitors suffering from the capacitor plague is asking for trouble right from the start.After having replaced the capacitors - preferably with 105 deg C types - try to movethose resistors as far away as they will go.

author: mictas
author_rank: Regular Contributor
timestamp: December 15, 2017, 11:55:15 am
content: Quote from: Messtechniker on December 15, 2017, 11:20:39 amWell Teac dosen't build anything high end, I mean I would love a Yamaha preamp and or just an amplifier, but I wasn't able to pick up one for free. Unlike the Radio, cassette and CD deck.Moving those two little electrolytics, I might be able to make some room, but if you want an even bigger screw up, behind those sorry looking large capacitors, is the speaker output.But yea, the ones I have picked to replace are 105 deg and a little higher in voltage, I have not ordered them yet.

author: ciccio
author_rank: Frequent Contributor
timestamp: December 15, 2017, 12:52:44 pm
content: Those resistors are the emitter resitors of the power stage. In normal use they do not heat up.The capacitors failed because they are crap....

author: mariush
author_rank: Super Contributor
timestamp: December 15, 2017, 01:12:16 pm
content: You should also replace those two capacitors that are squeezed between the two smaller resistors and the two large copper (looking) heatsinks. Look at the circuit board how it got dark from all the heat and image that heat going up the leads of those two tiny capacitors cooking their insides.You could try to also buy those two resistors in a larger size (like 7w or 10w rated) and leave the leads longer (use a bit of heatshink on the leads) and you could maybe use some thermal glue to stick the resistors to the back of those two big heatsinks, if they don't heat up much.Alternatively, you could drill one or two holes in those heatsinks and use thermal paste and a bit of wire to make the resistors stick to those heatsinks.Hell, maybe you'd be better off just buying some proper TO-220 heatsinks to replace those metal pieces, after all they're probably less than 1$ a piece. At least you won't have those ugly screws if you replace the heatsinks.

author: oldway
author_rank: Super Contributor
timestamp: December 15, 2017, 07:37:32 pm
content: It seems to be the same as the Goldstar GSA-5200.I found the service manual, but not for free...http://www.lg-goldstar.owner-manuals.com/GSA5200-service-manual-LG%20/%20GOLDSTAR.html

author: mictas
author_rank: Regular Contributor
timestamp: December 16, 2017, 12:38:43 am
content: Quote from: oldway on December 15, 2017, 07:37:32 pmWell that is cheaper, when I have found else where.Quote from: ciccio on December 15, 2017, 12:52:44 pmI already have some recovered heatsinks, I can pop on, but looking at their size, I am going to have to remove both the To220's and place them else where, along with the two smaller capacitors and the two resistors. I am wondering if putting up a steal shield between the transformer and using that space with a bit of strip board, with some posts to keep it off the chassis.

author: mictas
author_rank: Regular Contributor
timestamp: December 25, 2017, 05:27:06 am
content: So I am going to post this here.I seemed to have failed, for now. Well I need to look at getting the service manual next.

author: mariush
author_rank: Super Contributor
timestamp: December 25, 2017, 06:59:39 am
content: Hmm.. some feedback as I watched the videoJeesh, you're really paranoid about solder and stuff with those gloves. Just joking, it's ok if you don't like to get dirty.As I said, you should have replaced the two small capacitors under the resistors as well.The big capacitor orientation was easy ... just look at the circuit board, the negative is marked. Only write something down if it's different than the normal convention (negative = bar, filled part of circle etc)It often helps to add a drop of liquid flux and even some additional solder, before using the desoldering gun. Especially if they used lead free solder, just add a bit of leaded solder and your gun should suck the solder much easier.You tin the tip of your gun with solder burning away all that flux in the process and then you bring the gun tip to the existing solder which lead free (so more difficult to bring to liquid state) and which is still oxidized so it's harder for heat to transfer from your gun to the actual solder. Your soldering iron warms much faster so you can quickly go over everything you want to desolder, add a bit of solder, then as the solder cools down, use a flux pen or flux syringe to wet with solder with a bit of flux (preventing oxidation until you use the desoldering gun).24:00 it hurts... awful soldering technique ... use thicker solder wire, warm the tip to a higher temperature if it takes more than 2-3 seconds for the solder to melt. Add a bit of solder to tip so that heat transfers from tip to pcb and lead, then bring solder on the opposite side.. why the f.. are you wiggling the leads..Buy some liquid flux and use it.Here, learn the proper way to solder ... jump to 12:00 and watch to the end if you're impatient :no need to be so aggressive with the brush and cleaning, unless your solder has really aggressive flux. Most no-clean and rosin based fluxes can even be left on the circuit board without affecting anything. Use a bit of isopropyl alcohol if you really want to and that should be enough.You should look carefully at solder joints around that area that got so overheated over time, you may have cracked solder joints. Liquid flux and maybe wick the old solder with braid (or your gun) and apply new solder if you spot some dubious solder joint.

author: Seekonk
author_rank: Super Contributor
timestamp: December 25, 2017, 07:14:05 am
content: First stop listening to all those who say replace capacitors. If the capacitors were bad you would have had music with a big garbled hum. The amplifier section is on the other side of the heat sink. It could be the audio signal is just not getting to the amplifier section. Check the power resistors to see if a reasonable voltage is on each side. One not getting warm would be an indicator you are getting close These should heat up. Should be a small heatsink with a power transistor. These often fail open. If the output terminals are just tens of mv from ground that is a good sign. This problem could likely be in the lower voltage power supplied to low level amplifier circuits. Repair is a process of analysis, not guessing.

author: mictas
author_rank: Regular Contributor
timestamp: December 25, 2017, 09:29:41 am
content: Quote from: mariush on December 25, 2017, 06:59:39 amThis is all rather still new for myself.Quote from: mariush on December 25, 2017, 06:59:39 amWhen using that desoldeing gun, I try to add a bit of solder before I start attacking the pins, I do have the smallest tip you can buy, I just have not remembered to use it.Quote from: mariush on December 25, 2017, 06:59:39 amI have no excuse, I do have flux cream/paste and keep forgetting to take it out and use it.Quote from: mariush on December 25, 2017, 06:59:39 amI have not seen those Pace videos for a long time, and I did not think of re-flowing the solder joints, thank you for that. As for solder braid, I have never been good with the stuff I own, it just might be too cheap.Quote from: Seekonk on December 25, 2017, 07:14:05 amPersonally, I am happy with how the unit seems to power off, as I said before the light would just turns off and now it will dim off.While, I understand what you are saying in regards to the capacitors, it is still something i would like to get practice in replacing.My skills in complaint level repair, is lacking. Before I do anything else with the amplifier, I want to get my hands on that service manual that oldway linked to and I still do want to move off the power transistors and clean and use the heatsinks, I have shown before.Well I took a stab at it and no real change, but I do know, something to tackel next.Thank you both.

author: Ysjoelfir
author_rank: Frequent Contributor
timestamp: December 25, 2017, 10:07:35 am
content: Amplifier Repair is actually quite simple most of the times. A systematical atempt is easy to do since you basically just have two "paths" that you need to take a look at - amplifier and power supply. If the PSU is good (thou shall check voltages!) and the device is powered on and gets into either a protection mode or just doesn't do anything or kills your speakers them you look at the amplifier path. If you don't hear anything I usually start from the speaker terminals, searching with a scope where the signal appears. If there is distorted, muffled, way to silent sound I usually start from the audio input. that is usually a quite effective way.First thing before that is of course visual inspection and five minutes of educated guessing

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: December 25, 2017, 10:17:15 am
content: Merry Xmas. (Thoughts: Does that mean it's suitable for mains suppression duty?)Those capacitors may not be faulty. It was normal for the outer insulating sleeve to bulge at the end like that.If it uses an STK thick film module, then 99% chance that is blown, and that it was blown by faulty speaker wiring which shorted.(The reason both channels get blown is that the user invariably swaps the speakers over, putting the short across the other channel and blowing that too.)The board does look blackened, which suggests that the output has been overloaded or shorted.BTW, never connect any speakers you value directly to an amplifier under test. Either use a pair that don't matter, or do initial tests with a current limiting resistor in series with each. Reason is that if these DC-coupled amps are faulty they can put the whole DC supply voltage across the speaker, which will destroy it in seconds.

author: oldway
author_rank: Super Contributor
timestamp: December 25, 2017, 10:58:36 am
content: QuoteBefore replacing anything, you should first follow this procedure:- technical documentation (service manual) (share here if possible)- visual inspection and check all the fuses.- check if there are the 2 jumpers between preamp. outputs and main amplifier inputs on the rear panel.- check if there is a relay to protect the speakers or not.- power on the amplifier and check if something is getting too hot or not and if the protection relay switch on or not- check all the power supplies for voltage and ripple- check the 2 main power amplifiers by injecting a 1000Hz 500mV signal at the rear panel main amplifier input...(resistive output load)-check the 2 preamplifiers by injecting 200mV of various frequencies in the aux input and measuring output at rca output jack "preamp output" at rear panel. Check also all the tone and filters controls.Report all the results here.

author: mictas
author_rank: Regular Contributor
timestamp: December 25, 2017, 12:31:49 pm
content: Quote from: IanMacdonald on December 25, 2017, 10:17:15 amIts a good thing I used scrapped speakers, because after reading your post, I freaked a little and checked the speakers, with my DMM I was getting 7.1 ohms on each.Anyway, looking at the heatsink, a SANYO STK4161 apeards to be slapped onto it.Quote from: oldway on December 25, 2017, 10:58:36 amI am unable to do anything detailed, as of yet, but.List- technical documentation-http://www.lg-goldstar.owner-manuals.com/GSA5200-service-manual-LG%20/%20GOLDSTAR.html(Will be buying later in week, if possible)- visual inspection and check all the fuses.- visual inspection appears okay, but has not been tested.I also found, but I still need to test a XR2206 kit from eBay, but it was working last time I used it.

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 25, 2017, 01:10:55 pm
content: Quote from: ciccio on December 15, 2017, 12:52:44 pmNot at 68 ohms each, they aren't emitter resistors.

author: mzacharias
author_rank: Frequent Contributor
timestamp: December 25, 2017, 01:24:38 pm
content: These are the common causes of a symptom such as yours:If the unit has a speaker protection relay, use an ohm-meter to see if any of the amplifier inputs to the relay are shorted to either main + or - power rail. If so, one channel is bad on the output IC (that is what it uses?) A "blown channel" in other words. The module would have to be replaced or the unit scrapped.Again with reference to the amp inputs to the speaker relay, with the unit running, a DC voltage measured at the speaker relay (the amp input to the relay again) would be a fault. DC on one channel, maybe the output IC or related components, even solder connections.DC on both channels points to a power supply fault.Most "dumb" protection circuits include a single rectifier off the power supply, lightly filtered for a sharp cut-off at power down. Small value electrolytics in this circuit often fail, so the relay is never allowed to come on, or take a long time to come on if the cap is marginal.

author: Seekonk
author_rank: Super Contributor
timestamp: December 25, 2017, 10:29:59 pm
content: Just what equipment do you have? Measure the output voltage with no speaker. There are always a few millivolts. If not then it could be a protect circuit. I didn't see any relay, but who is going to take an hour to watch a stupid video. No way anyone needs a manual to fix this.

author: mictas
author_rank: Regular Contributor
timestamp: December 26, 2017, 04:40:09 am
content: Quote from: Seekonk on December 25, 2017, 10:29:59 pmSo, the Right channel was out putting 43.0 mV and kept dropping until I disconnected it at 39.4 mV. While the Left channel was out putting 20.1 mV and it was stable.

author: Seekonk
author_rank: Super Contributor
timestamp: December 26, 2017, 07:57:03 am
content: Those numbers sound reasonable, some drift is natural. It is unlikely there is any protect circuitry being activated. Whith a speaker connected, does it make any hiss. Any amplifier should produce some random noise. Have the volume control turned up. Google the amplifier module, likely a STK.... number and find the audio input pin. Just touching an unconnected test lead to that should get you some buzzing. That would indicate the amplifier is working. Try this also with some high level input like tape. Not sure what your audio source has been.Whatever is at fault is likely common the the right and left channel. That strongly points to power supply that powers preamp and tone controls. Check the voltage on each side of the power resistors. They should be getting warm. Check for little or no voltage. If they are nearly the same voltage, a transistor may have opened up. Form follows function. A resistor generally drops voltage, a power resistor should get warm in the power supply section, Amplifier electronics doesn't work without voltage to power it.It is all a mater of making a chart of things you know and things you don't know about a piece of equipment, what is needed to make it function.

author: oldway
author_rank: Super Contributor
timestamp: December 26, 2017, 11:19:58 am
content: You are not stupid, just you do not have the experience or the knowledge to repair an amplifier.IN such a condition, you have no chance to repair this amplifier without any technical information you need to understand how it works.So, the minimum necessary is the schematic diagram of this amplifier.Your video is totally ridiculous and I recommand you to delete it from youtube.About safety, what is important are safety glasses to protect your eyes if something explode.You do not provide us with any usefull information as the type of the audio module (STK ?), nor information on a possible relay, nor inputs and outputs, ....Based on photos found on the internet,- there is no loudspeaker protection relay- There is no output preamp / power amp input .... but, there are record outputs which could be use to check if input selector and preamp are working or not.To troubleshoot low frequency amplifiers, you need very few instruments: a multimeter and a signal tracer / injector signal (like this onehttps://www.velleman.eu/downloads/0/illustrated/illustrated_assembly_manual_k7000.pdf). No need for power supply, oscilloscope, or function generator.A variac is very useful, but a current limiter with 100W incandescent lamp in series can suffice.With regard to the failure, it is either a power supply failure or a fault in the input selection circuits or preamplifiers.The power amps look ok.

author: mictas
author_rank: Regular Contributor
timestamp: December 26, 2017, 11:59:00 am
content: Quote from: oldway on December 26, 2017, 11:19:58 amBack when I got this, it looked like a cheap Amplifier and since I have started collecting separate modules, until I get myself something else, this will do.The STK is 4161 and a symbol for two. Also, no relays are in this unit.Mine is like this, but with another brand logo:http://www.hifi-pictures.net/amplifiers-home/Goldstar%20GSA-5200/amp.htmAnd I do not own a variac, yet.Quote from: Seekonk on December 26, 2017, 07:57:03 amI quick search and I found thishttp://www.pselectronic.cz/pdf/1122/1122121.pdflI will not be firing up the amplifier for a while, but I do not recall hearing any kind of hum. I will check this again, at a later date.

author: mictas
author_rank: Regular Contributor
timestamp: June 04, 2018, 11:36:38 am
content: So, it has been sometime, but I had an idea to trace out the schematic for this audio amp, seeing if I can bypass the control chip IC102 LC4066 and IC103 LC4066 and this is what I have come to.This happen a few days ago at Hackerspace while talking with someone about this unit.By the looks of things, I can plug something into thePlayorRECports to see if something is wrong with the IC103 LC7815 on the back to see if I get any audio pass through to the speakers on the output.If that fails, I can just tap into Pins 2 or 4, 8 or 10 to see if it is something do to with IC102 LC4066.But then it could be IC 201 STK-4171 2Am I correct or?I'll add a link the schematic here -->

author: Harb
author_rank: Regular Contributor
timestamp: June 04, 2018, 11:45:54 am
content: Unless you want to take this on as a challenge, and I am all for repairing things, but if not, bin it and go to the op shop and pick up something like an old pioneer etc that is built properly.....I would say thats the poorest design I have ever seen.....

author: mictas
author_rank: Regular Contributor
timestamp: June 04, 2018, 11:57:15 am
content: Quote from: Harb on June 04, 2018, 11:45:54 amYea this is more of a project, and I am more wanting to confirm what I have been thinking.That and if I was to get anything, it would be a black Yamaha amp and or preamp, because the tape deck, radio, and CD player I have where all black Yamaha boxes.That and I have only see home theater systems for about $40 in opshops.-- Removed--Yea, I get that a lot. And when I have seen something like that, they are $40 or so.

author: mictas
author_rank: Regular Contributor
timestamp: June 06, 2018, 06:54:59 am
content: So I fired up my oscilloscope and started probing about and I think I understand why this is a stupid design, the audio passes through two of the front panels, before exiting out back onto the logic board.I did check the two IC's and they both had an audio signal coming out of the output, however were the audio leaves the logic board and travels into the first front panels, I found audio.But on the output from the front panels, I found no audio.Next step, is trying to workout the front panels...

author: Chris56000
author_rank: Frequent Contributor
timestamp: June 06, 2018, 06:32:24 pm
content: Hi!I've got one of these things myself making yukky noises, so I've got the circuits!!!Watch this space, I'll stick it in my Dropbox to share when the seller releases it!!!Chris Williams

author: mictas
author_rank: Regular Contributor
timestamp: June 06, 2018, 09:38:43 pm
content: Quote from: Chris56000 on June 06, 2018, 06:32:24 pmI have the service manual to the Goldstar CS-5200, which seems pretty much the same, its just missing the fuses on the speaker output.--Update--Now that I think of it Chris56000, try cleaning the pots on your amp, that should help with the sounds.

author: Chris56000
author_rank: Frequent Contributor
timestamp: June 07, 2018, 05:59:31 pm
content: Hi!https://www.dropbox.com/s/ahixzj7ctd1bal3/GSA5200_SM_LGGOLDSTAR_EN.pdf?dl=0This covers the whole caboodle, made up of four parts, of which the GSA-5200 is just the amplifier part!You should be OK to fix it now, along with the Sanyo STK-etc., data sheet!Chris WilliamsPS!Please let me know it's the correct one - there are PCB reference nos in the manual which should match those in your gear!

author: mictas
author_rank: Regular Contributor
timestamp: June 08, 2018, 01:21:00 am
content: Quote from: Chris56000 on June 07, 2018, 05:59:31 pmThanks, but I already have that.Yesterday, I got a bit of help and we found that the STK-4171 2 looks to be dead.