Hi All,
Just a quick question about my Sharp stereo amplifier model SM-1122.
I was in the garage listening to the radio using the Sharp model ST-1122 AM/FM stereo tuner when I heard a loud POP. Immediately there was quite a bit of hiss/static along with the music, similar to when you get this analog tuner close to a station but not really on it yet. I walked over and looked at the tuner signal meters and they were close on but I adjusted the dial anyway. No help.
It's an old set up and I have used DeOx on the switches and buttons once about 3 years ago. So every once and a while I have to cycle thru the buttons on the tuner (AM/FM, mono, air check) to fix little issues. I cycled thru the buttons on the tuner, no help. Then I cycled thru the buttons (loudness, mono)(phono, tuner, tape, aux) on the amp. No help.
That's when I noticed that no matter what source button I selected I now had a constant loud hiss that is not affected by the volume control.
Has the amp finally given up the ghost?
R/
Jim
Just a quick question about my Sharp stereo amplifier model SM-1122.
I was in the garage listening to the radio using the Sharp model ST-1122 AM/FM stereo tuner when I heard a loud POP. Immediately there was quite a bit of hiss/static along with the music, similar to when you get this analog tuner close to a station but not really on it yet. I walked over and looked at the tuner signal meters and they were close on but I adjusted the dial anyway. No help.
It's an old set up and I have used DeOx on the switches and buttons once about 3 years ago. So every once and a while I have to cycle thru the buttons on the tuner (AM/FM, mono, air check) to fix little issues. I cycled thru the buttons on the tuner, no help. Then I cycled thru the buttons (loudness, mono)(phono, tuner, tape, aux) on the amp. No help.
That's when I noticed that no matter what source button I selected I now had a constant loud hiss that is not affected by the volume control.
Has the amp finally given up the ghost?
R/
Jim
Everything can be repaired.
If you open it up, take clear pictures and post.
Sounds to me like some capacitor failing. Look for bulging capacitors.
Other option is, some transistor may have failed.
You need schematics and multimeter, at least.
Good luck.
If you open it up, take clear pictures and post.
Sounds to me like some capacitor failing. Look for bulging capacitors.
Other option is, some transistor may have failed.
You need schematics and multimeter, at least.
Good luck.
Take extra care with testing and tinkering with models like this one. The power amplifier section is based on a 2-channel hybrid package device, Sanyo STK043. This is essentially a prefab of all the amplifier semiconductors in a single big, multileaded package that is attached to a heatsink. Not only are they unforgiving to blunders like shorts but they're also obsolete and most types are now irreplaceable. Substitutes and copies may be available online but few of these are anything like the original design or quality inside. Many copies fail when driven near their rated power and don't seem to sound right anyway.
Service manual: Sharp SM-1122H - Manual - Stereo Integrated Amplifier - HiFi Engine
Service manual: Sharp SM-1122H - Manual - Stereo Integrated Amplifier - HiFi Engine
adason, Ian,
Thank you for your responses. Just want to let you know I followed up on my post.
adason, I'm the original owner and would you believe it, I still have all the paperwork on the whole 4 component set up, to include schematics. I opened the case and did a quick inspection but found nothing obvious. And after reading Ian's response, I've decided to accept the fact that the good times are over and move on to a newer amp or receiver.
R/
Thank you for your responses. Just want to let you know I followed up on my post.
adason, I'm the original owner and would you believe it, I still have all the paperwork on the whole 4 component set up, to include schematics. I opened the case and did a quick inspection but found nothing obvious. And after reading Ian's response, I've decided to accept the fact that the good times are over and move on to a newer amp or receiver.
R/
Don't despair - If you liked the old amp 🙂 it may not be all that difficult to fit a kit or pre-assembled and working dual channel amplifier module, complete on its own little PCB with support circuit, in the space to the rear of the original board and utilising its sheetmetal heatsink. A module can most likely be used with the same preamp and controls as before and function with the same dual rail power supply. You only need to identify the appropriate points on the original board to make the power supply, signal input and power output connections, after removing the old module.
Before you do anything though, check that amplifiers or maybe just one of them, is actually dead, by testing for any DC more than 100mV across the output terminals. Also test whether there is actually DC power (+/- approx. 24V) on the amplifier board. The amplifiers themselves are direct coupled to the speakers, via the switch contacts in the headphone jack and switches can be misleading if the contacts are dirty or the output fuses there have blown for some reason.
There are kits - some too simple but costing less than $10, others unnecessarily complex for this application, larger and a bit more expensive but based on excellent dual chipamps such as TDA7265. This chipamp can deliver 20-25W/channel on the same power supply, has internal protection and sounds fantastic so we can't complain about value.
Before you do anything though, check that amplifiers or maybe just one of them, is actually dead, by testing for any DC more than 100mV across the output terminals. Also test whether there is actually DC power (+/- approx. 24V) on the amplifier board. The amplifiers themselves are direct coupled to the speakers, via the switch contacts in the headphone jack and switches can be misleading if the contacts are dirty or the output fuses there have blown for some reason.
There are kits - some too simple but costing less than $10, others unnecessarily complex for this application, larger and a bit more expensive but based on excellent dual chipamps such as TDA7265. This chipamp can deliver 20-25W/channel on the same power supply, has internal protection and sounds fantastic so we can't complain about value.
Is this happening on both channels alike? It may suggest a power supply related issue if so.
If this was a capacitor failing, it would have had to be rather violent and may be visible. Otherwise abrupt faults would rather point towards semiconductors.
As typical for Sharps of the time, this amplifier appears to use an STK hybrid for the power amp. Let's hope it's not that.
If this was a capacitor failing, it would have had to be rather violent and may be visible. Otherwise abrupt faults would rather point towards semiconductors.
As typical for Sharps of the time, this amplifier appears to use an STK hybrid for the power amp. Let's hope it's not that.