I have an amp that has 4 output transistors. 2 NPN in parallel and two PNP on parallel (Sanyo D1047 and B817C).
I have one bad PNP.
So I know I have to replace both PNPs, but do I need to also replace the pair of NPNs?
If so, do I need to match the NPNs to the PNPs and how the heck do I do that? Note that these are listed as complementary pairs by Sanyo.
Since each pair is wired in parallel, do I need to match the transistors within each pair? I would think that since they are in parallel, they essentially work as one unit and it would be more important to match across the pairs.
Finally, they are used Sanyo products available, but for new I can get either OnSemi or unbranded. I'm thinking if I can get used Sanyos form a good amp that may be better as they will more likely match the original specs and any required matching would have been likely done by the amp manufacturer.
I have one bad PNP.
So I know I have to replace both PNPs, but do I need to also replace the pair of NPNs?
If so, do I need to match the NPNs to the PNPs and how the heck do I do that? Note that these are listed as complementary pairs by Sanyo.
Since each pair is wired in parallel, do I need to match the transistors within each pair? I would think that since they are in parallel, they essentially work as one unit and it would be more important to match across the pairs.
Finally, they are used Sanyo products available, but for new I can get either OnSemi or unbranded. I'm thinking if I can get used Sanyos form a good amp that may be better as they will more likely match the original specs and any required matching would have been likely done by the amp manufacturer.
Ideally the PNPs should be replaced as a pair, but NPN and PNP will differ simply because of physics. So the NPNs won't need to come out. Look around well before turning on though, something caused it to cook.
Thanks.
Any thoughts on used Sanyos vs getting them from On Semi?
I'll been trying to find the problem but everything else looks OK so far...
Mods: if you can change the title for this to "Replacing..." I would appreciate it. Auto correct did me wrong ;-)
Thanks
Any thoughts on used Sanyos vs getting them from On Semi?
I'll been trying to find the problem but everything else looks OK so far...
Mods: if you can change the title for this to "Replacing..." I would appreciate it. Auto correct did me wrong ;-)
Thanks
Did the PNP fail shorted? If so it would have stressed the NPNs with high currents.
I have found that if any output transistors fail in an amplifier, it won't be long before more of them do so. You can either just replace the defective parts and expect to have to do it again and again relatively soon, or just replace everything and have a reliable amplifier for years to come.
I don't believe in "used" output transistors. If it was my amplifier I would replace all of the output transistors with brand new devices, both channels.
Take care,
Doug
I have found that if any output transistors fail in an amplifier, it won't be long before more of them do so. You can either just replace the defective parts and expect to have to do it again and again relatively soon, or just replace everything and have a reliable amplifier for years to come.
I don't believe in "used" output transistors. If it was my amplifier I would replace all of the output transistors with brand new devices, both channels.
Take care,
Doug
Thanks Doug.
I don't mind replacing all the transistors. It's only 4 ( one channel sub amp).
But, I am curious as to how a short (it was a short) on one side of the push-pull can affect the other side.
I don't mind replacing all the transistors. It's only 4 ( one channel sub amp).
But, I am curious as to how a short (it was a short) on one side of the push-pull can affect the other side.
Output transistors in older amplifiers often fail just with age. Years of use and abuse will weaken them until they finally let go.
If one side of a push-pull circuit shorts, this effectively puts the remaining transistor(s) across both voltage rails, and when the signal begins to turn them on they potentially conduct the full power supply current through them.
Take care,
Doug
If one side of a push-pull circuit shorts, this effectively puts the remaining transistor(s) across both voltage rails, and when the signal begins to turn them on they potentially conduct the full power supply current through them.
Take care,
Doug
Yes, always check the drivers and the rest of the circuitry when the output transistors fail, sometimes there are other damaged parts and sometimes there aren't. This depends on the design of the amplifier and sometimes just by chance.
The OP stated that he has found no other problems, and very often a shorted output transistor is the only thing wrong when an amplifier fails.
Take care,
Doug
The OP stated that he has found no other problems, and very often a shorted output transistor is the only thing wrong when an amplifier fails.
Take care,
Doug
If a transistor is wearing out from age then it is running at too high a junction temperature to be reliable. The others are likely running equally hot so you’re wearing those out too. Infant mortalities would usually go out quickly (first few hours). If you replace just the one pair you are rolling the dice on just his long the other pair has left on it. Unless you can point to a specific overcurrent event which would have excessively stressed that one dead device, which it sounds like you can’t identify.
The amp *might* have sufficient protection to prevent the other pair from going into overcurrent when one side shorts out. If it didn’t, you would have had at least one shorted in each side.
The ON Semi version *is* the Sanyo version. That’s where they got them from in the first place. I would suspect that they will not be around forever. They have slowly phased out a lot of the “good” Sanyo parts over time. Still making a lot of the SMD low/medium power stuff, ad they have other Fairchild TO-3P parts that are similar.
If the drivers, outputs, vbe multiplier and base-emitter resistors check out, go ahead and fire it up on a light bulb limiter.
Honestly I have never subscribed to the theory of transistors "wearing out". Something always kills them. Either running too hot or another fault caused the part to fail.
Onsemi has discontinued the 2SB817 recently (now listed as Obsolete on their site). Their website makes no mention of of the 2SD1047, though ST make that part (it's commonly used in linear power supplies!)
Onsemi has discontinued the 2SB817 recently (now listed as Obsolete on their site). Their website makes no mention of of the 2SD1047, though ST make that part (it's commonly used in linear power supplies!)
My experiences repairing literally hundreds of amplifiers over the years, some of which were never abused or run hot, and with no other faults, disagrees with you. Whatever the failure mechanism might be, it's a proven fact that output devices in older equipment do fail spontaneously for no apparent reason.
Take care,
Doug
Take care,
Doug
Thanks wg_ski. Good info re: On Semi. I'm going to pick up a full set and maybe some extras so I can do some matching.
I have a variac and will fire it up on that. I haven't had a chance to dig into the amp more, but I did check the resistors and they were fine. I'll check the driver transistors. The fuse blew on the amp and that may have protected the other side.
I have a variac and will fire it up on that. I haven't had a chance to dig into the amp more, but I did check the resistors and they were fine. I'll check the driver transistors. The fuse blew on the amp and that may have protected the other side.
Turns out the supplier for the On Semi transistors has a minimum order qty that I can't meet.
My options look to be a myriad of unbranded transistors sold on eBay or Amazon or a substitute from Mouser or Digikey.
I'll likely go with a generic version of the original part as I don't have time to dig through data sheets to compare specs right now.
That said, if anyone could recommend a susubstitute from major semi conductor manufacturer, that would be great.
My options look to be a myriad of unbranded transistors sold on eBay or Amazon or a substitute from Mouser or Digikey.
I'll likely go with a generic version of the original part as I don't have time to dig through data sheets to compare specs right now.
That said, if anyone could recommend a susubstitute from major semi conductor manufacturer, that would be great.
The Fairchild C5242/A1962 (or the FJA house numbered versions - same exact part) were the reason the D1047/B817 were discontinued. There was no real “need” to keep making both - they were the same basic class of device. Just Toshiba’s version (originally). The ‘N’ cased C5200/A1943 or MJW0281/0302 could be used as the next step up if you stay with ON, or find out whatever Sanken is making these days (seems to change more often). If you wanted something more sturdy, you could go with MJW3281/1302, but prices start ratcheting up and half the time you won’t find stock. I tend to stick with ON, unless the amp had Sankens in there to begin with.
The “supplier” wouldn’t happen to be Rochester, would it? They buy up all the end runs at EOL but don’t deal in onesey twoseys.
The “supplier” wouldn’t happen to be Rochester, would it? They buy up all the end runs at EOL but don’t deal in onesey twoseys.
I was tempted to say use Onsemi's MJW0281/0302 but they have a lot higher capacitance. Probably wont be an issue... probably!
I'd agree on the choice of 2SC5242/2SA1962 as a viable alternative... just get them from a proper supplier such as Mouser or Digikey!
I'd agree on the choice of 2SC5242/2SA1962 as a viable alternative... just get them from a proper supplier such as Mouser or Digikey!
The MJW’s have a higher capacitance because they are a bigger transistor. The 0281 is the same size as original Toshiba 3281. ON 3281 is even BIGGER. Those were acquired back in the Motorola days, and Motorola liked overkill.
Transistors dont wear out.
They usually fail because something has put them outside SOA.
Breakdown voltage has been reached.
Too much current through them has over heated and blown them.
Occasionally static from hands can damage them.
Fault in a previous section of amplifier has forced them out of SOA.
Short on output like from shorted speaker or wires.
They usually fail because something has put them outside SOA.
Breakdown voltage has been reached.
Too much current through them has over heated and blown them.
Occasionally static from hands can damage them.
Fault in a previous section of amplifier has forced them out of SOA.
Short on output like from shorted speaker or wires.
Second breakdown causes an instantaneous catastrophic failure. But overheating IS a wear-out mechanism. At 300C junction temp it will happen FAST. At 250C it will last a while, but you won’t get good service life out of the product. Down where it is SUPPOSED to be run you get hundreds of thousands of hours. Hotter it runs, the shorter before it fails. And the effects are cumulative.
You may be surprised just how high a Tj consumer product runs at when it’s turned up LOUD. And how far outside the second breakdown limited SOA. How many recievers have you seen with only one output pair and +/-55 volt supplies? Would you do that? Hell no but penny pinching manufacturers do. They count on the excursions being short enough not to matter, but with a heavy hand on the volume knob it might not be.
Temperature CYCLING is yet still another wear out mechanism. Transistors can only take so many cycles from 25 to 150C (junction temp) before they die. Plastic packages take less of them than the metal ones did. What actually happens is the thermal resistance rises with temp cycling and eventually it gets hot enough to just wear out.
You may be surprised just how high a Tj consumer product runs at when it’s turned up LOUD. And how far outside the second breakdown limited SOA. How many recievers have you seen with only one output pair and +/-55 volt supplies? Would you do that? Hell no but penny pinching manufacturers do. They count on the excursions being short enough not to matter, but with a heavy hand on the volume knob it might not be.
Temperature CYCLING is yet still another wear out mechanism. Transistors can only take so many cycles from 25 to 150C (junction temp) before they die. Plastic packages take less of them than the metal ones did. What actually happens is the thermal resistance rises with temp cycling and eventually it gets hot enough to just wear out.