My official JTM45 kit build thread. Pics & CLIPS ADDED

franc · Post by **franc** » Sat Sep 01, 2007 1:41 pm

So it's either the 68ks, tube or Sozo...

Post by **VelvetGeorge** » Sat Sep 01, 2007 1:47 pm

Great! Please recheck the voltage on V1, pins 1 and 3.

You're hot on the trail.

VG

mushmouth · Post by **mushmouth** » Sat Sep 01, 2007 2:02 pm

VelvetGeorge wrote:Great! Please recheck the voltage on V1, pins 1 and 3.

You're hot on the trail.

VG

V1:
Pin 1 = 272.8 VDC
Pin 3 = .902 VDC

PS: Franc, I swapped the v1 tube earlier and it did the same thing, so the tube is ruled out too. Unless it were a socket.

mushmouth · Post by **mushmouth** » Sat Sep 01, 2007 2:10 pm

NOTE: I still had the replacement sovtek in v1 on that last reading. Put the JJ back in and got this on v1:

Pin 1: 275.6
Pin 3: .990

That's a pretty big change from where they were right after the build when taking the first readings off every pin. Back then they were 190.1 on pin 1 and 1.526 on pin 3.

mushmouth · Post by **mushmouth** » Sat Sep 01, 2007 3:13 pm

Ok. I now replaced that first .022 sozo for the old mustard and that wasn't the problem either. I measured the capacitance of the sozo out of the board and it came up at 21.97 so it's fine.

Edit: I pulled the first set of 68k AB's and replaced them with the little beige ones. No change. It's not that first set of 68ks EITHER.

*scratching head*

Ok. So now I've also removed the allen bradley left 270k of the pair and replaced it. No change...

Post by **VelvetGeorge** » Sat Sep 01, 2007 3:51 pm

With the amp on....carefully!!!!! touch your meter lead to each side of the .022. See if you hear anything. The volume knob needs to be up to hear it.

VG

mushmouth · Post by **mushmouth** » Sat Sep 01, 2007 3:54 pm

VelvetGeorge wrote:With the amp on....carefully!!!!! touch your meter lead to each side of the .022. See if you hear anything. The volume knob needs to be up to hear it.

VG

one meter lead on each side? Or ground to chassis and touch each side one at a time with the positive?

I guessed, ground to the chassis, then tapped each side of the lead with the positive meter lead. On the jack side of the lead it made a quiet buzz. On the tube side of the lead it made a loud POP when it makes contact.

mushmouth · Post by **mushmouth** » Sat Sep 01, 2007 4:03 pm

I've also disconnected a couple wires needed to lift the board high enough to see under it clearly and there are no wires being pinched, and no wires have come undone from the bottom of the board. I didn't check the little black ones connecting points under the board, but nothing was hanging out.

Has anyone looked back at my underboard wiring to see if anything was done improperly there?

mushmouth · Post by **mushmouth** » Sat Sep 01, 2007 4:05 pm

Also, if anyone thinks the preamp socket could be bad, let me know. If I find out in the next 90 minutes, I can still make it back to the store to get one. Otherwise I'm out of luck until tuesday.

To summarize:

It's not the jacks, the first 68k's, the first 270k, the first .022 Sozo, or the preamp tube in V1. With the amp on, if I tap the meter lead on the jack side lead of the first .022 I get a quiet buzz. If I tap it on the tube side of that .022 lead I get a loud "pop".

Hey George, what do you make of those pin 1 and 3 readings off V1?

franc · Post by **franc** » Sat Sep 01, 2007 5:10 pm

Weird....

It's almost like that first half of V1 simply is not working...

mushmouth · Post by **mushmouth** » Sat Sep 01, 2007 5:15 pm

franc wrote:Weird....

It's almost like that first half of V1 simply is not working...

I know. This sucks...

On the other hand, I stopped thinking about it and played the other input nearly dimed for the last 40 minutes or so. God DAMN that side sounds good!

CQ

PS: Are there any wires I should hard wire new wires over the top of the board to find out if a wire is bad somewhere? I don't know what else to guess. In my limited ability to understand what's happening, I'm pretty much out of ideas. George, what did the .022 tapping experiment indicate?

Post by **VelvetGeorge** » Sat Sep 01, 2007 5:17 pm

It must be the AB 100k on the V1a plate. Replace that with a normal carbon film.

VG

mushmouth · Post by **mushmouth** » Sat Sep 01, 2007 5:19 pm

what's the v1a plate? where on the board? The 100k pair v-formation in the upper left board? The left of the pair being "a"? IF SO, I just swapped that out and there was no change...

mushmouth · Post by **mushmouth** » Sat Sep 01, 2007 5:57 pm

New summary:

It's not:
the jacks
the first 68k's
the first 270k
the first .022 Sozo
the preamp tube in V1
or the v1a plate 100k (the left one of the v-formation)

With the amp on, if I tap the meter lead on the jack side lead of the first .022 I get a quiet buzz. If I tap it on the tube side of that .022 lead I get a loud "pop".

Post by **VelvetGeorge** » Sat Sep 01, 2007 6:32 pm

Touch the common terminal for the 68k's. And pin 2. You should have the same "pop" both places.

VG