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I handle some of the backline gear for the CBS Late Late Show, and the little Fender Princeton Reverb just came back in after running fine for a good year or so. Complaint was it had stopped working during one of the shows. Putting it up on the bench revealed all is working fine. Pounded on it, yanked on the input cable plug to see if I could induce jack problems, yanked on the molded spkr cable plug, another weak link in the late Fender models using those. Nothing I did invoked any stoppage of signal. So, I let it run all day with burst pink noise feeding it and put it aside, while diving into other repairs.
Following day, I started it back up, and it ran until I needed the bench it was sitting on, and I shut it down, set it aside for the next round.
After having pulled the Fender Twin Reverb I had just posted a thread on apart, which had massive solder joint fractures everywhere from their Lead Free Solder, I figured even though I never did find anything, and feared NOT having gone digging, it would come back to haunt me. So, I pulled it apart.
First, I was unable to extract the chassis from the cabinet. Not hung up on roof foil like normally happens with Twins and Deluxe Reverbs....this seemed to be hung up on the side wall Tolex covering. Took the handle off, turned it upside down, and incremented it's way out the back, finally coming free, while it being upside down, the other two tube shields reappeared that had been hiding inside the Reverb pouch somehow.
Pulled the front panel PCB off, the input jack PCB off, not seeing any obvious signs of solder fractures there, I then unplugged the xfmr wiring while marking the terminals or board, this actually being the first time I've had the Princeton Reverb reissue amp apart. After lifting up the main PCB, I did find a few questionable solder joints and repaired those, but nothing like what I found in the Twin last Friday. Cleaned up the flux, carefully set the board back down and re-assembled it, after re-soldering a couple joints on the front panel PCB.
When I powered it back up, it was pulling 1.06A/109W @ 120VAC, and I saw an ugly 60Hz waveform on the scope. Wasn't like that before I pulled it apart! Sigh......
Pulled the main PCB back up, to discover the power tube grid wire for V5 had gotten under the nylon PCB standoff, crushed the wire in half, grounding the grid. Removed both ends of the wire & replaced it. Put it back together again, making sure nothing got under any standoff, and powered it back up. Pulling the same mains current again! Measured the bias voltage at the pot, -36.7V, but 0VDC at the power tube grids. Uh oh. Shut down, then did continuity measurements between the bias pot and the pair of 220k bias feed resistors to the grids, and didn't find the connection. Pulled up the schematic, looked for clues, then pulled up the PCB again, noting this time I had failed to plug in the front panel board. After looking at the connections from the bias pot, that wandered up to the header to connect to the Tremolo controls before going back onto the main board to feed the power tube grid circuit. Sigh............
Put it back together, reconnected the FP PCB connections, now had bias, now had signal, looked at the clock to discover I had missed my late afternoon bus to go home. Sigh.......
Amp is back together, still running as it had before I took the time to pull it apart. Something tells me there's pilot error at the Late Late Show that began all of this. But, I guess nothing like being humbled by ones' own carelessness in the process! I did try...........
Following day, I started it back up, and it ran until I needed the bench it was sitting on, and I shut it down, set it aside for the next round.
After having pulled the Fender Twin Reverb I had just posted a thread on apart, which had massive solder joint fractures everywhere from their Lead Free Solder, I figured even though I never did find anything, and feared NOT having gone digging, it would come back to haunt me. So, I pulled it apart.
First, I was unable to extract the chassis from the cabinet. Not hung up on roof foil like normally happens with Twins and Deluxe Reverbs....this seemed to be hung up on the side wall Tolex covering. Took the handle off, turned it upside down, and incremented it's way out the back, finally coming free, while it being upside down, the other two tube shields reappeared that had been hiding inside the Reverb pouch somehow.
Pulled the front panel PCB off, the input jack PCB off, not seeing any obvious signs of solder fractures there, I then unplugged the xfmr wiring while marking the terminals or board, this actually being the first time I've had the Princeton Reverb reissue amp apart. After lifting up the main PCB, I did find a few questionable solder joints and repaired those, but nothing like what I found in the Twin last Friday. Cleaned up the flux, carefully set the board back down and re-assembled it, after re-soldering a couple joints on the front panel PCB.
When I powered it back up, it was pulling 1.06A/109W @ 120VAC, and I saw an ugly 60Hz waveform on the scope. Wasn't like that before I pulled it apart! Sigh......
Pulled the main PCB back up, to discover the power tube grid wire for V5 had gotten under the nylon PCB standoff, crushed the wire in half, grounding the grid. Removed both ends of the wire & replaced it. Put it back together again, making sure nothing got under any standoff, and powered it back up. Pulling the same mains current again! Measured the bias voltage at the pot, -36.7V, but 0VDC at the power tube grids. Uh oh. Shut down, then did continuity measurements between the bias pot and the pair of 220k bias feed resistors to the grids, and didn't find the connection. Pulled up the schematic, looked for clues, then pulled up the PCB again, noting this time I had failed to plug in the front panel board. After looking at the connections from the bias pot, that wandered up to the header to connect to the Tremolo controls before going back onto the main board to feed the power tube grid circuit. Sigh............
Put it back together, reconnected the FP PCB connections, now had bias, now had signal, looked at the clock to discover I had missed my late afternoon bus to go home. Sigh.......
Amp is back together, still running as it had before I took the time to pull it apart. Something tells me there's pilot error at the Late Late Show that began all of this. But, I guess nothing like being humbled by ones' own carelessness in the process! I did try...........
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