I was thinking some more on this...
If these two transistors, the 2SA841's, are a recognised issue (and I don't know if they really are or not) and if you are really keen to try and get on with this then you could always get a couple of transistors from Maplin who have shops in many towns. Either a pair of BC556's or a pair of 2N5401's are suitable.
If you did do that then come back here before switching on and we'll confirm absolutely 100% you are fitting them the right way round as the pin outs are different.
If these two transistors, the 2SA841's, are a recognised issue (and I don't know if they really are or not) and if you are really keen to try and get on with this then you could always get a couple of transistors from Maplin who have shops in many towns. Either a pair of BC556's or a pair of 2N5401's are suitable.
If you did do that then come back here before switching on and we'll confirm absolutely 100% you are fitting them the right way round as the pin outs are different.
Mooly I already ordered 2SA970's and they have arrived along with the multi meter. They where only cheap though the trans so if need be i can order different ones as well.
Il probably have a look at it new years day when im off work as im out all day tomorrow and in work Monday. Its taken months to get this far so now that its all ready to go there is no point rushing it. The system is older than I am so I few more days wont upset it too much
.
Cheers.
Il probably have a look at it new years day when im off work as im out all day tomorrow and in work Monday. Its taken months to get this far so now that its all ready to go there is no point rushing it. The system is older than I am so I few more days wont upset it too much
.Cheers.
Well don't rush with it
The 2SA970 seems to have the same pin-outs as the 2SA841 (as far as my data sheets show). When you fit the transistors make absolutely sure you measure the DC offset BEFORE connecting speakers. That is to say, the DC voltage at the amplifier speaker terminals MUST be zero volts.
If you have ANY doubts over the transistor pin outs then ASK and we'll identify them using your meter first.
The 2SA970 seems to have the same pin-outs as the 2SA841 (as far as my data sheets show). When you fit the transistors make absolutely sure you measure the DC offset BEFORE connecting speakers. That is to say, the DC voltage at the amplifier speaker terminals MUST be zero volts.
If you have ANY doubts over the transistor pin outs then ASK and we'll identify them using your meter first.
They should be but I would never take anything on trust...
Two choices... fit 'em and see what gives or at least do a basic test on them. Did you get a meter ?
If you fit them read the post above regarding NOT connecting speakers until you have confirmed there is NO dc voltage across the speaker terminals.
Good luck... ask if your not sure
Two choices... fit 'em and see what gives or at least do a basic test on them. Did you get a meter ?
If you fit them read the post above regarding NOT connecting speakers until you have confirmed there is NO dc voltage across the speaker terminals.
Good luck... ask if your not sure
I am resurcting this thread rather than starting a new one as this post is about the same amp. The amp is still working fine and sounding great but has developed a rather worrying foible. When I switch it on and off it makes my plasma tv, which is connected to the same double gang power socket (and therefor circuit) go off for a split second. Its as though it causes a sudden lack of power.
Is this a sign of something a miss with the bigger capacitors not storing enough power or something?
Another thing is that when i switched it off it would take a few seconds for the sound t gradually fade away. Now it goes off almost immediately.
Is this a sign of something a miss with the bigger capacitors not storing enough power or something?
Another thing is that when i switched it off it would take a few seconds for the sound t gradually fade away. Now it goes off almost immediately.
No problem... easy one first.
The amp carrying on for a while and fading out, and now carrying for less time indicates a few possibilities. Most, or quite likely... the bias of the output stage has drifted a little and its drawing a wee bit more current. This setting is something that you should check as per the manual. More current means it pulls the charge out or the reservoir caps quicker. Another possibility you MUST check. That the DC offset is still zero volts DC on both channels. Thats just means measuring the DC voltage across the speaker with no signal. If there is an offset then that too pulls more current. And least likely... the caps are failing.
TV going off when you switch the amp on and off. I would guess the switch in the amp is arcing and upsetting the PSU in the TV. Try the amp on a different socket. Check all the connections in the plug for security. Consider adding a supressor to the switch. The fact it does it when you switch off as well as on suggests arcing rather than a dip in supply voltage caused by a surge.
The amp carrying on for a while and fading out, and now carrying for less time indicates a few possibilities. Most, or quite likely... the bias of the output stage has drifted a little and its drawing a wee bit more current. This setting is something that you should check as per the manual. More current means it pulls the charge out or the reservoir caps quicker. Another possibility you MUST check. That the DC offset is still zero volts DC on both channels. Thats just means measuring the DC voltage across the speaker with no signal. If there is an offset then that too pulls more current. And least likely... the caps are failing.
TV going off when you switch the amp on and off. I would guess the switch in the amp is arcing and upsetting the PSU in the TV. Try the amp on a different socket. Check all the connections in the plug for security. Consider adding a supressor to the switch. The fact it does it when you switch off as well as on suggests arcing rather than a dip in supply voltage caused by a surge.
That sounds like arcing and it doesn't mean there is a problem with the amp or switch.
What happens is that when the switch breaks the connection, the transformer (being inductive) can generate a high voltage spike. The plasma TV will have a switch mode type power supply and that is probably being upset by glitch on the mains and momentarily doing a "reset" and shutting down and restarting. These things weren't around way back when the amp was current.
I assume you have them all plugged into a "good" wall socket as any high impedance problems in the mains supply can make the effect much worse. Maybe try the two on an extension lead and double adapter running from another socket in the house. Just eliminates stuff, thats all.
A fix should be a supressor and maybe a VDR (voltage dependant resistor) fitted across the primary of the transformer. It should be an easy (famous last words) and cheap problem to sort because ultimately there is probably nothing wrong as such.
What happens is that when the switch breaks the connection, the transformer (being inductive) can generate a high voltage spike. The plasma TV will have a switch mode type power supply and that is probably being upset by glitch on the mains and momentarily doing a "reset" and shutting down and restarting. These things weren't around way back when the amp was current.
I assume you have them all plugged into a "good" wall socket as any high impedance problems in the mains supply can make the effect much worse. Maybe try the two on an extension lead and double adapter running from another socket in the house. Just eliminates stuff, thats all.
A fix should be a supressor and maybe a VDR (voltage dependant resistor) fitted across the primary of the transformer. It should be an easy (famous last words) and cheap problem to sort because ultimately there is probably nothing wrong as such.
Something like this for the VDR,
B72207S0271K101 - EPCOS - VARISTOR, 21.0J 275VAC | CPC
you need a 275 Vac rating for UK mains
Supressing the switch if needed involves a capacitor that MUST be Class X or Y rated (suitable for continuous mains use and self healing) and perhaps a 10 ohm resistor in series with it and these placed either across the transformer primary or across the switch contacts (depends a lot on whether the switch is double or single pole).
Another thought is to try a surge supressor plug on the amp.
B72207S0271K101 - EPCOS - VARISTOR, 21.0J 275VAC | CPC
you need a 275 Vac rating for UK mains
Supressing the switch if needed involves a capacitor that MUST be Class X or Y rated (suitable for continuous mains use and self healing) and perhaps a 10 ohm resistor in series with it and these placed either across the transformer primary or across the switch contacts (depends a lot on whether the switch is double or single pole).
Another thought is to try a surge supressor plug on the amp.
I will look into this today Mooly thanks a lot as always .
Its really strange that its started doing this after I repaired the transistors. I'm glad it doesn't sound to you like anything too serious.
When the amp switches off the TV doesn't actually 'reset' and switch itself off like it does if the power is cut properly. The picture just goes into the center and goes into a sort of bright white flash and hangs there for half a second or so and then returns to a full picture. It look a bit like a really old tube tv would look when you cut the power. Cant be to healthy for the tv I suppose!
.Its really strange that its started doing this after I repaired the transistors. I'm glad it doesn't sound to you like anything too serious.
When the amp switches off the TV doesn't actually 'reset' and switch itself off like it does if the power is cut properly. The picture just goes into the center and goes into a sort of bright white flash and hangs there for half a second or so and then returns to a full picture. It look a bit like a really old tube tv would look when you cut the power. Cant be to healthy for the tv I suppose!
Try just unplugging the amp smartly and see if the TV still trips. The other thing, the time the amp runs on for when switched off depends how much energy is being puuled from the fully charged caps. So do those two checks... bias current as per the manual... and check the DC offset. Two minutes of a job
English only please. All other posts have been deleted.Hello guys need your help on the amplifier sc-335 shot in the right channel when the shot rewards floating voltage at the exit of the channel ... who will tell you what to check... or measure testers are available... I can give a link to the view of the given amplifier with its problem...