Hi Folks. I could really use some help repairing my Cyrus 2, Issue 6 (plastic case).
In particular I need to find a replacement for the MJE243 / MJE253 driver transistor pair. In my case, I contacted something while attempting to check the bias (for the heck of it) that caused MJE253 to become permanently shorted (thus causing the FS1 and FS2 fuses to blow when the Cyrus is powered on).
I can buy a MJE243 / MJE253 pair off of eBay, maybe elsewhere, but unlike the versions with the TO220 package that I have (which apparently can dissipate up to 40 watts at ambient) all the available pairs have a TO126 package where the dissipation capability is far lower. I don’t know whether that matters (or whether there’d be any other difficulties with the TO126 lead pitch, pinout arrangement, etc).
I’ve also read through a number of posts concerning alternative replacements for MJE243 / MJE253, but the only thing I saw that was specific to the Cyrus was a suggestion to use a BD139 / BD140 pair. Again, though, the dissipation values are quite a bit lower than with the pair I have (and, again, I don’t know whether there’d be other difficulties such as the pinout).
Any suggestions would be appreciated since I'm not confident that I could reliably figure it out myself. Just one more thing…
I had an “accident” while taking out the board and bent/banged one of the regulator heat sinks so hard that it drove the transistor through the board, tearing off two of the three solder pads and part of the associated traces. Does anybody know of a repair kit out there with at least appropriately-sized replacement pads and trace sections (the ones I’ve found are tiny - for cell phones and the like)?
Thanks.
In particular I need to find a replacement for the MJE243 / MJE253 driver transistor pair. In my case, I contacted something while attempting to check the bias (for the heck of it) that caused MJE253 to become permanently shorted (thus causing the FS1 and FS2 fuses to blow when the Cyrus is powered on).
I can buy a MJE243 / MJE253 pair off of eBay, maybe elsewhere, but unlike the versions with the TO220 package that I have (which apparently can dissipate up to 40 watts at ambient) all the available pairs have a TO126 package where the dissipation capability is far lower. I don’t know whether that matters (or whether there’d be any other difficulties with the TO126 lead pitch, pinout arrangement, etc).
I’ve also read through a number of posts concerning alternative replacements for MJE243 / MJE253, but the only thing I saw that was specific to the Cyrus was a suggestion to use a BD139 / BD140 pair. Again, though, the dissipation values are quite a bit lower than with the pair I have (and, again, I don’t know whether there’d be other difficulties such as the pinout).
Any suggestions would be appreciated since I'm not confident that I could reliably figure it out myself. Just one more thing…
I had an “accident” while taking out the board and bent/banged one of the regulator heat sinks so hard that it drove the transistor through the board, tearing off two of the three solder pads and part of the associated traces. Does anybody know of a repair kit out there with at least appropriately-sized replacement pads and trace sections (the ones I’ve found are tiny - for cell phones and the like)?
Thanks.
TO223 package is the original, TO220 are the wrong way around!
https://www.mouser.co.uk/c/semiconductors/discrete-semiconductors/transistors/bipolar-transistors-bjt/?collector- base voltage vcbo=100 V&collector- emitter voltage vceo max=100 V&mounting style=Through Hole&package / case=TO-225-3&product type=BJTs - Bipolar Transistors
Mouser stocks these obsolete parts.
https://www.mouser.co.uk/c/semiconductors/discrete-semiconductors/transistors/bipolar-transistors-bjt/?collector- base voltage vcbo=100 V&collector- emitter voltage vceo max=100 V&mounting style=Through Hole&package / case=TO-225-3&product type=BJTs - Bipolar Transistors
Mouser stocks these obsolete parts.
Attachments
My advice would be, don't buy semiconductors off eBay, to many fakes and remarked parts around.
I'm curious what you are looking at here. TO126 is the package for those devices and 15 watts (as Jon shows) is correct. That is when mounted on a heatsink held at typically 25C (the data sheets will specify). Sometimes the same parts can also be specified for free air (no heatsink) and that figure might be around 1 watt. Its still the same part though.
We've all done that and much worse. Easy fix using thin tinned stranded wire to run where the print did. Scrape the existing print and tin that and lay the tinned wire on it so it overlaps for a few mm. Easy 🙂
Also never use just solder to bridge small breaks, always always use wire. Although you have found one failed transistor it is unfortunately a fact that others may also get taken out under the fault condition and so you should carefully test and check. When powering the amp on with any new parts you should use a DBT (bulb tester) to prevent any high currents causing damage should any other issues persist.
From the web:
Use the TO-126 parts. Dissipation isn't a problem there.
I have repaired many Cyrus one, two and three integrated amplifiers. I Just repaired a Marantz 2270 receiver where the original TO-39 parts (big heat sink) were replaced with TO-220 parts. They were so hot you couldn't touch them dissipating 1 watt. I used TO-126 devices 2SC3421 and 2SA1358 on heat sinks to replace them. They run cooler than the originals and perform well. I have some MJE243 and 253 on hand, just a couple for my own use. There isn't anything special about them to be honest.
If you break a trace, always jump with wire along the same track. If it's really bad you may have to run insulated wire and shore things up with epoxy. In cases where damage is significant, you may be better with a small sub board for the regulators. Whatever you do, just make sure your repair is solid.
I have repaired many Cyrus one, two and three integrated amplifiers. I Just repaired a Marantz 2270 receiver where the original TO-39 parts (big heat sink) were replaced with TO-220 parts. They were so hot you couldn't touch them dissipating 1 watt. I used TO-126 devices 2SC3421 and 2SA1358 on heat sinks to replace them. They run cooler than the originals and perform well. I have some MJE243 and 253 on hand, just a couple for my own use. There isn't anything special about them to be honest.
If you break a trace, always jump with wire along the same track. If it's really bad you may have to run insulated wire and shore things up with epoxy. In cases where damage is significant, you may be better with a small sub board for the regulators. Whatever you do, just make sure your repair is solid.
Thanks much. I can't believe I got off on that large of a wrong foot (misread, assumed, etc).
I think I'm good now*, except to ask whether I should replace both MJE253's (i.e., Q37/Q38, where Q38 is the bad one), and indeed whether I should replace the MJE243's as well (Q33/Q34). I appreciate the advice to use a dim bulb tester, and have had the components to put one together for a while now.
*That said, for some reason the Cyrus 2 service manual lists MJE243/253 as having a TO-202 package, where what I have uses the TO126 package (as best I can tell).
I think I'm good now*, except to ask whether I should replace both MJE253's (i.e., Q37/Q38, where Q38 is the bad one), and indeed whether I should replace the MJE243's as well (Q33/Q34). I appreciate the advice to use a dim bulb tester, and have had the components to put one together for a while now.
*That said, for some reason the Cyrus 2 service manual lists MJE243/253 as having a TO-202 package, where what I have uses the TO126 package (as best I can tell).
Q33 and Q38 (the complementary pair). You are changing device types, so do the pair in that channel only. Don't mess with the working channel. If they look really baked (overheated), then change them as a precaution on the other channel. This is a reliability thing, it hasn't anything to do with "sound".
Many service manuals have typos. Ignore it, you can see the package.
Many service manuals have typos. Ignore it, you can see the package.