I'm looking to replace a power supply transistor, and I can't find any data about it. The schematic shows it as an npn transistor, but with no part number. The part is marked:
(Motorola M) 752
1075-1
I believe the second line is a 1975 date code - it comes from a power supply that was built around 1976.
The package is sort of like a TO-220, except that the plastic body extends onto the mounting tab, with a round clearing around the hole so that a bolt or standoff will contact the metal tab on top as well as on the bottom.
The 3 pins and the metal tab (top and bottom) are gold plated.
I've tried searching for BD742, MJE752, 2N752, etc. and can't find anything that matches.
Any help identifying this part and finding a data sheet would be appreciated!
(Motorola M) 752
1075-1
I believe the second line is a 1975 date code - it comes from a power supply that was built around 1976.
The package is sort of like a TO-220, except that the plastic body extends onto the mounting tab, with a round clearing around the hole so that a bolt or standoff will contact the metal tab on top as well as on the bottom.
The 3 pins and the metal tab (top and bottom) are gold plated.
I've tried searching for BD742, MJE752, 2N752, etc. and can't find anything that matches.
Any help identifying this part and finding a data sheet would be appreciated!
First thing you need to do is tell us exactly what this transistor is used in - bipolar power transistors in most cases aren't too difficult to substitute if a little is known about the circuit where it is used. There are exceptions of course, but hopefully not the case here.
Post a hand drawn schematic or link to a legally hosted copy of the schematic as having the context where it is used is helpful.
Post a hand drawn schematic or link to a legally hosted copy of the schematic as having the context where it is used is helpful.
The numbers you list are house part numbers for your particular power supply.
The package sounds like the old Motorola "case77", which became the TO-225. It was used in the early 70's and I remember building several Li'l Tiger audio amps in the late 60's that used that package. My ADD powered brain can't remember important stuff, but I can remember almost every transistor and tube number I have ever blown up. The Li'l Tiger used 2N4921 and 2N4918 transistors.
The case 77 package was popular back then and there was several types of transistors and SCR's made in that package. It is slightly smaller than the TO-220. Motorola also made a bigger package that had no plastic around the screw hole. It wasn't as popular.
Motorola spun off their discrete semiconductor business in the late 90's. ON Semiconductor is the new name for that business unit and they still make several parts in that package including the 2N4918 and 2N4921. One is PNP the other is NPN. There is a high voltage NPN part, the MJE340-D and a PNP, the MJE350-D. Perhaps one of these will work in your circuit.
The package sounds like the old Motorola "case77", which became the TO-225. It was used in the early 70's and I remember building several Li'l Tiger audio amps in the late 60's that used that package. My ADD powered brain can't remember important stuff, but I can remember almost every transistor and tube number I have ever blown up. The Li'l Tiger used 2N4921 and 2N4918 transistors.
The case 77 package was popular back then and there was several types of transistors and SCR's made in that package. It is slightly smaller than the TO-220. Motorola also made a bigger package that had no plastic around the screw hole. It wasn't as popular.
Motorola spun off their discrete semiconductor business in the late 90's. ON Semiconductor is the new name for that business unit and they still make several parts in that package including the 2N4918 and 2N4921. One is PNP the other is NPN. There is a high voltage NPN part, the MJE340-D and a PNP, the MJE350-D. Perhaps one of these will work in your circuit.
I thought the case was a Case 77 at first too. But it is not - on the Case 77, the plastic goes all the way to the hole. The case on my transistor looks just like this one:
Surplus Sales of Pennsylvania
(This part makes me suspect that for my transistor, 752 is the date code and 1075 is part of the part number.)
The package difference is important - several of these transistors get clamped between posts pressed into the PC board and an aluminum plate heat sink - so the package thickness is everything.
Additionally (and annoyingly), the circuit depends on an electrical connection from the top side of the tab, which is connected to the collector.
Answering the other question: The transistor is used as a pass transistor for a power supply controlled by an LM723 regulator IC. I need to find the real deal or a close match, because this power supply has three of them in parallel to get the necessary current output. (I know - I could replace all three with 3 new, matched transistors, but I'd rather not.)
Surplus Sales of Pennsylvania
(This part makes me suspect that for my transistor, 752 is the date code and 1075 is part of the part number.)
The package difference is important - several of these transistors get clamped between posts pressed into the PC board and an aluminum plate heat sink - so the package thickness is everything.
Additionally (and annoyingly), the circuit depends on an electrical connection from the top side of the tab, which is connected to the collector.
Answering the other question: The transistor is used as a pass transistor for a power supply controlled by an LM723 regulator IC. I need to find the real deal or a close match, because this power supply has three of them in parallel to get the necessary current output. (I know - I could replace all three with 3 new, matched transistors, but I'd rather not.)
Your link just takes me to a login screen. Post a picture of the real part 
To help determine a replacement what are the voltages and current we are working with.
The transistor has to be rated for the full supply voltage, not just the differential across it in use. What is the output output current of the PSU ?
Maybe also post pictures of the mounting arrangements.
To help determine a replacement what are the voltages and current we are working with.
The transistor has to be rated for the full supply voltage, not just the differential across it in use. What is the output output current of the PSU ?
Maybe also post pictures of the mounting arrangements.
I don't have any specs for the power supply - it's just good luck that I have a schematic, though non of the components on the schematic are labeled.
The load is a couple of relays and stepper motors - so it's a pretty inductive load. The load draws 2.8A "average power", according to the spec. (It's a pair of vintage Pertec 510 8" disk drives.)
The load is a couple of relays and stepper motors - so it's a pretty inductive load. The load draws 2.8A "average power", according to the spec. (It's a pair of vintage Pertec 510 8" disk drives.)
The case is called "Case 199-04". It is the same case used on the MJE3055K
(MJE3055K datasheet and application note, data sheet, circuit, pdf, cross reference, pinout | Datasheet Archive)
(MJE3055K datasheet and application note, data sheet, circuit, pdf, cross reference, pinout | Datasheet Archive)
PHoto of transistor and schematic
You make me figure out how to post a photo. Attached is the transistor, lying on the relevant portion of the schematic, if I did it right.
The unregulated power supply voltage (the input) is around 37V - probably designed for 40V. The output is 24V. The output continuous rating is probably 3A, with some additional rating for inductive surge. There is a protection diode on the output, together with an electrolytic cap, just to the right of what you can see in the photo.
You make me figure out how to post a photo. Attached is the transistor, lying on the relevant portion of the schematic, if I did it right.The unregulated power supply voltage (the input) is around 37V - probably designed for 40V. The output is 24V. The output continuous rating is probably 3A, with some additional rating for inductive surge. There is a protection diode on the output, together with an electrolytic cap, just to the right of what you can see in the photo.
Attachments
You seem to have got the hang of attaching pics but more here, post #11. The attach box is slightly different now to when I wrote this but it's near enough.
http://www.diyaudio.com/forums/digital-source/165754-sony-cd-player-cdp-102-a.html#post2171957
In all the years of being involved in electronics I have never come across that package.
You say the circuit depends on the connectivity from the tab. Without seeing the actual unit and how that works and how it all connects together mechanically it's hard to advise how to get around the mounting problem for other device. Spec wise there are dozens of suitable transistors. The collector is always the metal tab on any power device.
There must be ways and means of attaching other devices to the heatsink even if it means using an insulating kit and hard wiring the collector connection to where ever it goes.
http://www.diyaudio.com/forums/digital-source/165754-sony-cd-player-cdp-102-a.html#post2171957
In all the years of being involved in electronics I have never come across that package.
You say the circuit depends on the connectivity from the tab. Without seeing the actual unit and how that works and how it all connects together mechanically it's hard to advise how to get around the mounting problem for other device. Spec wise there are dozens of suitable transistors. The collector is always the metal tab on any power device.
There must be ways and means of attaching other devices to the heatsink even if it means using an insulating kit and hard wiring the collector connection to where ever it goes.
Yeah, I hadn't seen that package before - and all my googling couldn't find a data sheet for the thing either. That's why I came here
I ran into another thread out there that was discussing this package. Motorola stamped 'B', 'C', and 'E' on the leads, close to the body of the transistor - handy. However, they apparently used the same lead frame for some voltage regulators, without removing these markings - leading to some weird misunderstandings.
I have a second power supply of the same type (Alpha Power from Chatsworth, CA). It is also broken, so I took it apart and found that it had slightly different transistors. They had a different date code (the three-digit number), but the same 1075 number, which confirms that this is the part number, or at least part of it.
And - the transistors in the second power supply are in a TO-220 package. Same part number, different package... I found a good transistor in the bad power supply and moved it over - and it works. from a mounting perspective, the Case 199-04 is compatible (enough) with the TO-220.
But I would like to repair the second power supply as well. I guess I can use any reasonable NPN TO-220 transistor, so long as I replace all of the parallel transistors together. I see no down side to massively over-rating the transistors - say 10A or so. I need to figure out what is a reasonable minimum hfe for this regulator circuit.
Thanks for all the input on this. If anyone finds a data sheet for this "1075" (perhaps MJE1075?) transistor in a crufty old Motorola data book, I'd really appreciate a scan.
-Martin
I ran into another thread out there that was discussing this package. Motorola stamped 'B', 'C', and 'E' on the leads, close to the body of the transistor - handy. However, they apparently used the same lead frame for some voltage regulators, without removing these markings
- leading to some weird misunderstandings.I have a second power supply of the same type (Alpha Power from Chatsworth, CA). It is also broken, so I took it apart and found that it had slightly different transistors. They had a different date code (the three-digit number), but the same 1075 number, which confirms that this is the part number, or at least part of it.
And - the transistors in the second power supply are in a TO-220 package. Same part number, different package... I found a good transistor in the bad power supply and moved it over - and it works. from a mounting perspective, the Case 199-04 is compatible (enough) with the TO-220.
But I would like to repair the second power supply as well. I guess I can use any reasonable NPN TO-220 transistor, so long as I replace all of the parallel transistors together. I see no down side to massively over-rating the transistors - say 10A or so. I need to figure out what is a reasonable minimum hfe for this regulator circuit.
Thanks for all the input on this. If anyone finds a data sheet for this "1075" (perhaps MJE1075?) transistor in a crufty old Motorola data book, I'd really appreciate a scan.
-Martin
Yes, I thought of just using one transistor - that should work better than the original arrangement. But I actually care about how it looks when done - I want it to look as much as possible like it did originally. So I might use 3 transistors, where each one of them is capable of carrying the whole load.
That is the larger case that I was referring to. I couldn't remember the number on that one. I remember seeing those on the factory floor for only a few years. I have worked in a Motorola plant for the past 39 years. They came and went, and are rather expensive now. The popular MJE2955 / MJE3055 audio transistors were once made in that package. No parts are currently made in that package.
Check the pinout carefully if replacing with TO-220's. At least one of those oddball packages had the B and E leads reversed from the norm. It might have been this one.
If a customer placed a sizeable order with the factory Mot would screen whatever text the customer wanted on th the parts. This allows the customer to conceal the real number and charge big $$$ for replacement parts.
I will look through my old junk this weekend since I used them for audio amps back then, but I have recently tossed most of the old stuff.
I ran across some surplus parts SCR's that had the B, C and E marks.
No listing for MJE1075 in my old Mot transistor book, but my book may be too old. My bet is that it is a MJE3055. It was a very common and popular part for about 2 years, at least here.....we made the damn things. And yes, ours had a funny number on them too. They were used in battery chargers for police radios and........power supplies.
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