Working on Carver C4000 and could use some help

Dutch54

Dutch54

Journeyman
Joined
Jun 1, 2022
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Got it all recapped and did all the service bulletins but when on the Dim bulb tester Resistors R50, R51 get hot enough to burn the paint off of them, are they to small at 75 ohms 2watt. If so what would be a good size?
 
Got a schematic? I don’t think the resistors are the issue. There’s a fault someplace. Power resistors often run very warm. But they shouldn’t be hot enough to blister your finger.
 
Yes have a schematic and r50, r51 get hot enough to take the skin right off your finger.
My next question is are R50, R51 being used like emitter resistors and if they are do I need to cut the trace, and does anyone have a photo of where these two are on the board?
 
Dutch54 said:
Yes have a schematic and r50, r51 get hot enough to take the skin right off your finger.
My next question is are R50, R51 being used like emitter resistors and if they are do I need to cut the trace, and does anyone have a photo of where these two are on the board?
Click to expand...
It would help us help you if you shared a reasonable portion of the schem around R50 and R51
 
Hope this helps, r50 and r51 are around VR1, VR2 at top of page. Thanks for the help.
 

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Those resistors are in parallel with the regulators. There is a downstream fault. My guess is either a chip or electrolytic cap(s) in backwards. There is potential danger if it's a cap as it could become a projectile if allowed to fail. To troubleshoot use the nose and index finger to find something getting hot. I
 
wattsabundant said:
Those resistors are in parallel with the regulators. There is a downstream fault. My guess is either a chip or electrolytic cap(s) in backwards. There is potential danger if it's a cap as it could become a projectile if allowed to fail. To troubleshoot use the nose and index finger to find something getting hot. I
Click to expand...
Agree with Don, you have something downstream in backwards. There should be little to no heat, this is a preamp.
 
Yup
those resistors do not get hot.
in last update to the c-4000 they are eliminated

check the regulators are in correctly C9E4EA63-52B9-49D7-BEA3-E64D01CFC10A.png
 
The Power Supplies on the C-4000 are crap and that is why me and Glen used the Power Supply Boards we had ginned up. When installed, they keep the PS Voltage spot on at 12VDC. Did you go around the boards and check the 12VDC (+ and -)? We've seen them down near 8 volts or less. We changed out all the RC4136 IC's to new ones (old and noisy) and spliced in the power supply. The Carver PS is rudimentary at best. Glen also adds bypass caps to the RC 4136 chips.

Take it off the DBT and shoot it with the Laser Thermometer. Your DBT may also be messin with the regulators. Preamps don't generally need to be on a DBT, yer not messin with high rail voltages and if you do use A DBT, what size bulb are you using? Did you see all the threads we did on the C-4000???? With the C-4000 having a 250ma fuse in it, a dbt is a waste.

The rear amp is also a problem spot. It's full of obsolete parts and it takes a LOT of work to get them rebuilt. Do some browsing, there is a bunch of info available (either here or the Carver Site).

Here is the PS we use.

OH,As a side note, I have seen the stock power supply board installed one pin off causing that same issue.



C-4000 PS Mod.jpgPS.jpg
 
Dutch54 said:
Yes have a schematic and r50, r51 get hot enough to take the skin right off your finger.
My next question is are R50, R51 being used like emitter resistors and if they are do I need to cut the trace, and does anyone have a photo of where these two are on the board?
Click to expand...

]
DON'T cut any traces. Troubleshoot the thing. Get a laser Thermometer and check how hot the resistors are getting. they are designed to withstand finger burning amounts of heat. Some will handle 150C and that will take the fingerprints right off you finger (And get off the Dim Bulb). If they haven't smoked the board under them, like a 400/700 PL14-20, don't worry about it.
 
Use Ohms Law and find out how much (or how close you are to the rated wattage) current is flowing through and the voltage drop across it. You may be worrying about nothing.
 
You asked a bunch of questions that I can not answer because every time I turn it on it blows the fuse, but I do thank everyone for all your help so far.
 
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