Ampeg SVT-7 PRO switches off after 1 to 4 hrs then back on again

[Arbutt]

Hello all
I have a svt pro 7 in for the usual problem
I tested to confirm issues very random switches off and on again
I removed the board to`replace U2 , This has been replaced before and a heatsink glued on to it
Replaced for 3A2065 which is an uprated chip
Refitted the board tested working Screwed up for testing the following day

Following day, Dead !! Tried a heat gun on the u2 area, came on ,
Removed the board replaced all 3 electrolytics . As i fitted U2 on a socket, I put a new one in, still the same Refitted and still dead until you apply a little heat
I have used the heatgun and freezer spray, Once its on, no freezing will make it switch offpower supply-xx.pdf
Checked all soldering - all ok
I have tried the Heat/freezer on secondary side

Many thanks in advance
Mr A

[Jon Snell]

If U2 has exploded, replace it otherwise find out why it is either not starting or 'chirping'. If the latter check for short circuit secondary diodes..
R84 & R232 start up U2. Ensure the startup voltage arrives on pin 7. If using 3065, remove one of these resistors as the 3065 has its own start up network and will see the added voltage as overvoltage and shut down in some cases.

[g1]

Checked all soldering - all ok

I had a similar problem and all the solder looked good. I just went ahead and re-soldered the area anyway, and that fixed it.
With lead-free solder you can't really go by what it looks like.

[J M Fahey]

Hello all
I have a svt pro 7 in for the usual problem
I tested to confirm issues very random switches off and on again
I removed the board to`replace U2 , This has been replaced before and a heatsink glued on to it
Replaced for 3A2065 which is an uprated chip
Refitted the board tested working Screwed up for testing the following day

Following day, Dead !! Tried a heat gun on the u2 area, came on ,
Removed the board replaced all 3 electrolytics . As i fitted U2 on a socket, I put a new one in, still the same Refitted and still dead until you apply a little heat
I have used the heatgun and freezer spray, Once its on, no freezing will make it switch offpower supply-xx.pdf
Checked all soldering - all ok
I have tried the Heat/freezer on secondary side

Many thanks in advance
Mr A

The full schematic would *definitely* help.

WTF is U2, 3A2065, "all 3 electrolytics" ???????

You guys love to speak in tongues

[Arbutt]

If U2 has exploded, replace it otherwise find out why it is either not starting or 'chirping'. If the latter check for short circuit secondary diodes..
R84 & R232 start up U2. Ensure the startup voltage arrives on pin 7. If using 3065, remove one of these resistors as the 3065 has its own start up network and will see the added voltage as overvoltage and shut down in some cases.

Hi Jon Thanks for the info
I have decided to get the original U2 chip Ic 2A165 as i didn't have this fault before i changed it
All i was getting was it working ok for a few hours then switch off and restarts again
While i was looking for a supplier of the chips i saw a YT video of a guy replacing U2 for 3A2065 in the same amp
so thats why i upgraded, As soon as the new 2A165 come in, I will fit and hopefully it put this pain in the arse back out the door

[Arbutt]

I had a similar problem and all the solder looked good. I just went ahead and re-soldered the area anyway, and that fixed it.
With lead-free solder you can't really go by what it looks like.

Thanks G2 I did go over every joint and it came on, But once cold it refused to start again
As i posted earlier. I have order the 2A165 and will replace and see whats what
Thankfully i put it on a ic socket
Have a nice weekend
Mr A