I also let it warm up for an hour or so and still couldn't get the voltage lower maybe I should add a ground strap on F-2778 like F-2819?and I'm also gonna replace the D357 and B527 transistors on it.
AU-X1
- Thread starter Willy6
- Start date
Ronito6
Super Member
Interesting as regards the extra ground for the 2778.
Regarding the other stuff...
Which VRs/Trimmpots?
What is closest possible voltage doable for each test point on the 2778?
Any other unusual results measured?
Fun fact: VR 1 and 2 that are to be dialed to 47.5v on the 2778 are powered by the dual capacitors that Kale usually makes from two (well...4) regular caps.
Regarding the other stuff...
Which VRs/Trimmpots?
What is closest possible voltage doable for each test point on the 2778?
Any other unusual results measured?
Fun fact: VR 1 and 2 that are to be dialed to 47.5v on the 2778 are powered by the dual capacitors that Kale usually makes from two (well...4) regular caps.
Last edited:
Maybe I should replace those to.
What's weird is the trimmers are multiple turn type but they don't really change anything until I get down to the last 3 or 4 turns and then it go's from around -63 to -55 then that's it can't turn it in that direction anymore
I'm at work today so I don't remember which vr's are what but the two for -10V are dead on and the two for -47.5v are the ones I'm having troubles with
Ronito6
Super Member
Your trimmers are likely OK.
You can test them in place if you can reach the leads of those suspect VRs / trimpots.
With the unit off, use a multimeter to test the change of resistance.
Attach one probe to the trimmer's center lead and one to to an outer lead.
Turn the trimmer knob and see if the resistance rises or falls as you turn.
Only one of the outer leads will work for this, the other will show no reaction when the trimmer knob is turned.
You can test them in place if you can reach the leads of those suspect VRs / trimpots.
With the unit off, use a multimeter to test the change of resistance.
Attach one probe to the trimmer's center lead and one to to an outer lead.
Turn the trimmer knob and see if the resistance rises or falls as you turn.
Only one of the outer leads will work for this, the other will show no reaction when the trimmer knob is turned.
Last edited:
Ronito6
Super Member
I forgot to ask...
Apparently the way I suggested for adjusting and dialing in the driver voltage current worked.
Did measurements from the emitters have different readings from what you measured at the page 12 TP ?
Last edited:
Yes at the test points they would barely go to 12mv but on the emitters I dialed them in to a perfect 25mv
Ronito6
Super Member
Ah! That agrees with my experience.
The SM we all use for the X1 must be for a version that no one has.
TP point for the drivers shown on page 12 were likely phased out very early on in the factory response to address the X1's oscillation problem.
I'm thinking of soldering some teflon insulated wires on to the test points behind the emitters to access them easier and cap them off when not in use..
The voltages on the F-2917,18 cards are set right on and so is F-2771 but I'm getting no reading on F-2770 yet and on the flat amp board both trimmers are set right on.I ordered all of the replacement transistors for the whole amp so I'm gonna go back through and replace every one of them and then see what happens.
What happened about the -47.5v adjustment ? - there seems to be mention that the -10v is OK but not the -47.5v ?
Note that they tell you to adjust for -47.5v because this regulator should mirror the +47.5v that the other half should output. there are 2 +47.5 // -47.5 regulators.
If you are still getting +/-63v out of these regulators they are not doing any regulating, the series pass transistors TR05, 06, 07, 08 are turned hard on.
Note that they tell you to adjust for -47.5v because this regulator should mirror the +47.5v that the other half should output. there are 2 +47.5 // -47.5 regulators.
If you are still getting +/-63v out of these regulators they are not doing any regulating, the series pass transistors TR05, 06, 07, 08 are turned hard on.
Ronito6
Super Member
Wondering about this too.
Some details reporting the VR# plus the TP# voltage readings will help toward our better understanding of what's happening with your F-2778 board.
As you already know your F-2778 it should measure:
VR03 measures -10.5v at TP01
VR04 measures -10.5v at TP02
VR01 measures -47.5v at TP03
VR02 measures -47.5v at TP04
If you could fill in the following it will help with our understanding.
VR03 measures ?????? at TP01
VR04 measures ?????? at TP02
VR01 measures ?????? at TP03
VR02 measures ?????? at TP04
Finally, many 2sb257 and 2sd357 have legs painted black as a bit of insulation.
Changing out all of them would call for some hFe pair matching.
It's a pain but the X1 really needs all the stability you can give it
Last edited:
Even though those regulators tested good with my peak tester they all have black corrosion on the leads so I went ahead and placed an order at mouser and I chose KSC2690A to replace 2SD357 and KSA1220 for 2SB527.
Even if the black stuff is paint I'm still changing them out and I'll try to match them up the best I can. as I recall the old ones weren't matched very well the hfe were all different and I pulled and tested them one at a time so they're all back in there original spot.
But that^^^ doesn't necessarily mean that the series pass transistors are bad, there could be several reasons for this...
Ronito6
Super Member
Those cut traces are a factory mod and shouldn't be a cause for concern.
Harolda's and my donor X1 have the same mod.
You can see it pointed out in in a photo in one of Kales X1 threads, and in one of Amp8's postings on his site.
So it may appear to be an amatuer hour PC mod, but it's a straight from the factory mod that just looks amateurish.
If it is the cut traces are what you are indeed pointing out, have no worries.
Or is it something else?
Harolda's and my donor X1 have the same mod.
You can see it pointed out in in a photo in one of Kales X1 threads, and in one of Amp8's postings on his site.
So it may appear to be an amatuer hour PC mod, but it's a straight from the factory mod that just looks amateurish.
If it is the cut traces are what you are indeed pointing out, have no worries.
Or is it something else?
Last edited:
Yes cut tracks but on the other unit the trace is not cut.
