Recaping 20y/o S.A.T Amplifix amplifier, anything else?

So I have this 20 year old S.A.T Amplifix amplifier that went silent on the left channel a while ago. Pre-amp works fine on both channels but there comes nothing from the left speaker output.

It didn't happen in any dramatic catastrophic way. I was listening to music one evening and suddenly the left channel goes silent for a couple of seconds before it comes back for a couple of minutes again and then it goes silent again and doesn't come back. I continue with another amp I had lying around and put the S.A.T aside for troubleshooting later some day. Tried it one week later and then both channels worked fine, and they did for a week but then left channel went out again and since then it has never come back.

Can't see any cracked solder joints and some people have told me to try replacing the capacitors, so that's what I am going to do.

Is there anything else I should order and replace while I'm at it? New caps will cost me €25 and shipping €20 so if there is anything else that typically goes bad with age then I'd like to replace it too.
 

rayma

Member
2011-04-29 8:37 pm
Just replace the electrolytic (and tantalum if present) capacitors.
Also look for discolored resistors and check their values.
Check the emitter resistors (fractional ohm) in the output stage for value if you can.
Otherwise verify the voltage drop is about the same for all the emitter resistors.
 
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Can't see any tantalum capacitors on the board, just electrolytic. Only one slightly discoloured resistor (colour is a bit faded) but it measures 5 ohms just like the other three similar resistors so I guess it's fine.

How do I know which resistors are emitter resistors? Sorry but I don't know anything about electronics or amplifier design. There are eight 0.16ohm resistors pretty close to the transistors and the massive heatsink. Are they the ones you are talking about?

How do I check voltage drop?
 

rayma

Member
2011-04-29 8:37 pm
The emitter resistors are usually larger, block-style parts near the output transistors, connected in series with
the transistor emitters (hence the name). Sounds like the 0.16 marked parts you see. Use your DVM
to measure the DC voltage across each one (one lead on each end of the resistor), but many meters cannot
accurately measure the small DC voltage present. Be careful not to short anything with the probes.
 
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Okay, I assume I should have the amplifier powered on and with a source connected? Shall I have anything connected to the speaker outputs too?

I don't have any fancy multimeter, just this cheap digital one Digital Multimeter UNI-T UT33D - ToolBoom

I know this forum doesn't like large images but I don't want to scale it down so I'll just post a link to a high-res photo of the amplifier board https://i.imgur.com/Ef0HWsD.jpg

You can see the eight 0.16ohm resistors by the bottom. You can also see the slightly faded colour resistor above to the left.

I wont be replacing the six big white capacitors. They look fine to me, no bulging and I can't find any values written on them anywhere and I was told that if any of them had failed it wouldn't kill just one channel and leave the other working just fine.
 
Okay, I'll get new relays too. The ones on the board are Omron G5LE-117P-PS which seem to be discontinued now (not surprising since they are 20 years old).

I don't know much about relays but I did some reading and it seems like I want SPST-NO (or A) contact form and 24V coil voltage.

Would the Omron G5LE-1A4-DC24 or G5LE-1A-DC24 work as a replacement? The difference seems to be that the 1A4 is fully sealed and the other has just "flux protection". Shall I get the fully sealed one?
 
Got the parts yesterday (even delivered by a friend who is a mailman) and today I had time to work on it. The small caps were a pain to replace. The new caps were much bigger and the legs were too thick so they didn't fit through the holes in the PCB. Had to get a little creative and solder them on the holes. Not a lot of space either for the soldering iron in some places. But managed to get all of them in place. The big ones were harder to remove but much easier to put in the new ones since the new ones were smaller than the old ones.

It also turns out that I ordered the wrong relays. The ones on the board have five legs and the ones I got have four. Guess that's the difference between SPST-NO and SPDT, and I have SPDT I suppose and the ones I ordered were SPST-NO.

I decided to try the amp anyways and it turns out that replacing the capacitors didn't make any difference. Right channel sounds fine but left channel is completely silent.

My next thing to try will be to try to swap the relays around. If the problem moves with the relays then I know one of the relays are bad. If the left channel is still dead the problem has to be somewhere else and then I don't know if I have enough knowledge to actually repair this amplifier.
 
Swapped the relays today and it is still the same problem. Sound from right channel but nothing from left channel. So the relays are fine.

I do have this slightly discoloured resistor though. See this image https://i.imgur.com/SJT0R50.jpg

Compare it to the one to the right. There are four of these and this one is discoloured and I think it belongs to the left channel. I measured all four and they all measure 5 ohms on my multimeter. I tried soldering off one of the legs and measure it again and it is still five ohms.

I have sent an email to the Bladelius company, which is sort of the same company that made this amplifier back in the day. Hopefully someone there has some knowledge about this amplifier.
 
Looking at physical condition is not a productive way to debug an amplifier.
You need to check for DC voltage coming out on the speaker jacks now. Your soldering adventures may have induced bad joints, which could cause DC offset. No speaker required.
I really don't respect connecting component leads to one side of the board. If I couldn't buy parts with the same diameter lead or smaller, I'd drill a hole in a 2 sided board next to the pad, insert the leg, and bend over to the pad underneath. A General pin vise and a set of #30-#60 drills is handy for this. Usually #42 or #48 works for component leads.
Relay legs need to match. Or you need to drill new holes for the new relays and run patch wires over from the old holes.
Buying components from the US in Europe is unproductive. If RS in the UK can't supply them, try reichelt in Germany. Mouser has a warehouse in SWE but I don't know how to detect they are going to fulfill from a US warehouse. Farnell operates in most countries and always tells me on the part line if the stock is out of the US. I don't order those.
Possible causes of channel silence besides the relay, are interboard connections oxidized or loose, or the volume pot wiper oxidized. Other amps have source selector switches that the contacts can oxidize. These can be removed & replaced, or sprayed out, or in some cases have to be replaced.
You can trace the music through the amp with an analog voltmeter with a 2 vac or 20 vac scales. 2 vac in the front sections, 20 vac at the VAS or later. Put a .047 uf or .1 uf >100 v cap in series with the negative probe to prevent response to DC signals. I energize the amp with the earphone jack of a pocket radio. check with a earphone to make sure it is tuned on station. Line level input is up to 2 vac but earphone jacks can go to 7 vac so don't go too loud. If tuned to a rock station you can see the beats of the music on the pointer of the meter. Oscillations would be high & steady. A scope will work too, but have short lives due to all the tantalum & electrolytic capacitors. I use a simpson 266xlpm meter from 1985.
Where the music stops, that stage has the problem. Can be a bad solder joint although a 20 year old amp you would think those would have showed up beforehand. Unusual weather, like cold in a new residence that wasn't in the old, can make bad solder joints show up. If touching a point with the meter probe causes the music to start again, then it quits again later after some seconds or days, then that point was the bad joint. I usually leave a cheap (salvage from auto scrap yard) speaker attached while doing this. 1000 uf 50 vnp capacitor series the speaker can prevent damage from DC out the speaker jack. (or two used polar 2200 caps line to line). Takes patience to find these.
Best of luck.
 
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ManUtd

Member
2003-09-23 2:02 pm
Hi,
I have this amplifier and i have replaced some caps in it.
Now i get Blinking Zero when i put the power cord.
I hear a click from rele when i put in the powercord.
I am not sure if remote is working, because it has no indicators on it.
Anyone got some usermanual or service manual for this amp?
Or if some could tell me what blinking zero in display means.
Thanks,