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No internal power Valvestate 8280
No internal power Valvestate 8280
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Old 4th July 2018, 07:34 AM   #1
prospect is offline prospect
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Default No internal power Valvestate 8280

Hello,


I have a valvestate 8280 which seems to have a problem with the pre-amp.
No lights on the front panel and it produce no sound via the input jack on the front. The problem just occured after the amp hasn't been used for a while.


I assume a broken cap somewhere but there are no visual damages. Any ideas what to check to identify the problem?
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Old 4th July 2018, 09:44 AM   #2
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Check the 12v supply is present.
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Old 4th July 2018, 05:44 PM   #3
prospect is offline prospect
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I am not sure I have measured what you suggested.
Since the Pre-amp is feed by power from the transformer I thought that was the only mains input but I see a possibility that the Reverb/PSU feed the Pre-amp as well.


I found a schematic on the net which I included below.
I measued on the Reverb/PSU board.


It is 12VAC in from the transformer.
FS1 and FS2 have high resistance. Don't know which values it should be.
REG1 is possible to move so it needs to be resoldered.
No voltage between pin 3 or 4 and 8 in connector 1(pins on the left hand side).


If high value on FS1 and FS2 indicates that they are gone, can the problem with REG1 causes that?
Replace REG1 as well?
Attached Images
File Type: jpg Reverb PSU_Page_5.jpg (940.1 KB, 37 views)
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Old 11th July 2018, 09:20 PM   #4
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by prospect View Post
FS1 and FS2 have high resistance. Don't know which values it should be.
They seem to be fuses. Resistance should be very low (fraction of an ohm.) High resistance tells you that both fuses have blown.

Quote:
Originally Posted by prospect View Post
REG1 is possible to move so it needs to be resoldered.
Without seeing photos, I have no idea. Are you seeing that the solder joints that hold REG1 to the PCB have actually let go? Or is REG1 still firmly soldered to the board, but there is a loose screw holding it to its heatsink? Are you seeing other evidence of damage (burned smell, charred board, etc)?

Quote:
Originally Posted by prospect View Post
No voltage between pin 3 or 4 and 8 in connector 1(pins on the left hand side).
Since the fuses that supply power to the board are blown, this is to be expected. You won't find any voltage anywhere on the board till the fuses are replaced, and the fault fixed so they don't blow again.

Quote:
Originally Posted by prospect View Post
If high value on FS1 and FS2 indicates that they are gone, can the problem with REG1 causes that?
Replace REG1 as well?
Failure of REG1 could blow both fuses, but it is not the only possibility. For example, a failure of IC1 could also blow both fuses.

I can't see what you're seeing since there are no photos - but if you're very sure that REG1 has been damaged, then certainly replacing it is a good step to take. Just be careful not to damage anything else in the process of replacing it!

-Gnobuddy
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Old 11th July 2018, 09:53 PM   #5
JonSnell Electronic is offline JonSnell Electronic  United Kingdom
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Watch out for any heatsink compound and silica insulators if fitted.
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Old 11th July 2018, 10:21 PM   #6
prospect is offline prospect
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I will post picutres when I am home again next week.


It is possible to wiggle the REG1 a little so the solder seems not to be firm any more.
I need to remove the PCB to study the solder more closely.


There are no heatsink for these components.
I do not see any other signs of that there are any problem with the PCB.
So, I do not know if REG1 is damaged or has casued the blown fuses.
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Old Today, 03:02 PM   #7
prospect is offline prospect
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Now I have had possibility to included photos.
PCB1 and 2 is the reverb/PSU.
Solder crack is close up on the Reg1 solder there cracks are visible.


Otherwise, no visible damage on the PCB.
Attached Images
File Type: jpg PCB 1.jpg (874.0 KB, 1 views)
File Type: jpg PCB 2.jpg (906.5 KB, 1 views)
File Type: jpg Solder crack.jpg (507.3 KB, 1 views)
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