bing says hifiengine has a c4000 schematic. type "carver c4000" in the search box.
eserviceinfo.com has the m400 schematic, but no t suffix.
Distortion in old amps is often a corroded connector, too much oxygen. These can be scraped off with a pick or wire brush. Also electrolytic coupler caps can dry up and cause odd sounds. e-caps are the time limiter on electronics - carver used pretty good ones probably, but 20 years can dry up any bottle.
A third source of problems is the volume pot, which can be replaced, or the source-line switch or whatever switch contacts are in the soundpath. Harder to clean than connectors.
eserviceinfo.com has the m400 schematic, but no t suffix.
Distortion in old amps is often a corroded connector, too much oxygen. These can be scraped off with a pick or wire brush. Also electrolytic coupler caps can dry up and cause odd sounds. e-caps are the time limiter on electronics - carver used pretty good ones probably, but 20 years can dry up any bottle.
A third source of problems is the volume pot, which can be replaced, or the source-line switch or whatever switch contacts are in the soundpath. Harder to clean than connectors.
you might look here.
Replacement outputs for Carver M400?
for your replacement transistor, also you will probably have an open resistor or 2. Check the drivers.
You should replace both outputs.if you use these.
MJ15022 Bipolar Transistors - BJT | Mouser
The "g" version should be fine.
Replacement outputs for Carver M400?
for your replacement transistor, also you will probably have an open resistor or 2. Check the drivers.
You should replace both outputs.if you use these.
MJ15022 Bipolar Transistors - BJT | Mouser
The "g" version should be fine.
Last edited:
If you blew output transistors, likely drivers are stressed too. At first level do a double diode test with DVM to ensure they are not blown. Better would be a Vcbo test on them. Put 12 v c to e on a transistor through a 47 k resistor with the base open (use correct polarity). If a series current meter shows much current, more than a few microamps, throw it away. Good first test for counterfeit transistors too.
Marginally stressed power transistors can have a lower Vcb voltage on the DVM diode scale than the new ones do. These can blow their tops when rail voltage is put on them. Use a 100 W incandescent bulb series the AC voltage to test. Also wear safety glasses. My TO3 tops hit the ceiling.
At worst case, rail voltage leaking out the base line of blown output transistors can blow through the drivers all the way back to the input stage. I've had to replace op amps, diodes, VI limiter parts, various Vi resistors capacitors also op amp rail capacitors protector circuit parts etc. 126 parts in one PV-1.3k amp.
You can luck out. The $20 PV-4c I bought had blown output transistors, and nothing else.
Marginally stressed power transistors can have a lower Vcb voltage on the DVM diode scale than the new ones do. These can blow their tops when rail voltage is put on them. Use a 100 W incandescent bulb series the AC voltage to test. Also wear safety glasses. My TO3 tops hit the ceiling.
At worst case, rail voltage leaking out the base line of blown output transistors can blow through the drivers all the way back to the input stage. I've had to replace op amps, diodes, VI limiter parts, various Vi resistors capacitors also op amp rail capacitors protector circuit parts etc. 126 parts in one PV-1.3k amp.
You can luck out. The $20 PV-4c I bought had blown output transistors, and nothing else.
Last edited:
It's been a while since I've worked on one of those but I think I replaced all of the outputs with MJ15024/25s, MJ21193/94s would be OK too. That amp is a real bugger to work on so it just made more sense to replace them all while it was apart.
I see MJ15016 written under the C3000 on the schematic. MJ15015/16 transistors were kind of the cheapos in the Motorola line back then.
Craig
I see MJ15016 written under the C3000 on the schematic. MJ15015/16 transistors were kind of the cheapos in the Motorola line back then.
Craig
Yes, the MJ15015/6’s are junkers with a beta of about 7 at 15 amps. Bean counter ecomomics at work. They are used in the rail commutators, so it’s safe to change them with better/faster devices like the 15024. Then all the parts are the same, and the commutators draw less off their driver circuits, giving you a smidge more output power.
Yeah, more than likely collateral damage. If an output transistor is shorted, but the amp doesn’t immediately go into some over current condition, something in series with that transistor has gone open. Which is probably a good thing with this amp. That funky phase-controlled transformer does weird things when you overload it, which makes diagnostics harder when you try to troubleshoot.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.