Foreplay 3 amp no output (Paramount)

[Mr. Self-destruct]

Needle nose twist on that transistor brings to life. I reflowed a few times. . It's on.      Nervous to touch anything. I've been staring at this for hours can't find loose wires.

 

[Mr. Self-destruct]

Poking on power supply board does not drop it out anymore I'm sending a video of me slightly twisting the transistor on the shunt board. I totally hear you and I agree on the wire. I just cannot find one and I've reflowed a lot on here and I'm feeling it's the transistor. https://youtu.be/Y3v7Z-IcCmQ

 

[Mr. Self-destruct]

I could assure you that it's only doing that when I twist that transistor not the board I could flip that board around and move it and tweak it and nothing happens. only when I twist that transistor

 

[Mr. Self-destruct]

Listening to music now. it will drop out after a few minutes but then come right back without touching anything.

 

[Mr. Self-destruct]

Is replacing the Transistor a bad idea? I'm kinda leaning toward that.  It seems like that's where the problem is stemming from.  When the amp is good I'm seriously tugging on all the wired connections and I can't replicate it unless I turn that transistor or does it by itself

 

[Paul Birkeland]

Go for it, you may find a broken wire when you remove that PC board

 

[Mr. Self-destruct]

I get it. I wish i could find said broken wire. C4s. That board has been up for a while. She's been holding steady for an hour plus so far. Reflowing n2n907 seems to been showing the best results. That transistor seems to have the most sensitivity. 

 

[2wo]

Is it possible you have a damaged trace? Check for a crack in the vicinity of that transistor, right were it forms the eyelets ...John

 

[Mr. Self-destruct]

Kinda seems like it. She's holding pretty steady as of now since reflow.

 

[Mr. Self-destruct]

I can't see if any cracks by trace. Too small. I replaced the Transistor 2n2907a,  it plays longer, cuts out a few seconds then comes back on for a while, the twisting of Transistor isn't cutting in and out like previous video. So I'd say it's a little better, but not fixed. I can't get it to cut out manually. I moved every wire and can't replicate it. It will cut out by its self, when I touch certain metal parts, with a metallic probe,like the Transistor I can hear static clicking in speakers like some sort of discharge. I go to sleep thinking what it could be. When it cuts out the d2 led on the b side remains lit.

 

[Mr. Self-destruct]

Barely Touched (A) side 2n2907a transistor collector w meter probe, amp turned off.  Meters other probe was not connected to anything so it could have been a bic pen, anything metallic.
Therefore since the 2n2907a transistors Collector goes to the MJE5731A transistor's emitter, that is also sensitive.
When the amp cut out I touched the metal probe to 16  Randomly and it came back on. A wooden stick does not do anything.  has to be metallic touching it. Tapped 5731a emitter, amp cut out, Touched 5731 base, came on. Those points seem to be the only point that makes a slight tick in speaker. The 2 transistors on A side. Also the center most csd01060 rectifier will Emmitt ticking thru speaker when metallic probe touches. It will also bring amp back on. Touching the mje350 w probe also cut off amp. Probing 907a base will turn it on.

 

[Mr. Self-destruct]

The 12at7 wouldn't have anything to do with this issue would it? because half of it operates as an actively loaded hybrid shunt regulator. I dont know, just asking.

 

[Paul Birkeland]

You have two amps and each has a 12AT7, so you can simply swap the tubes between amps to check for that.

 

[Mr. Self-destruct]

Doing that now. Just thought I'd ask to see if that's absolutely out of the question. Also the power choke tabs are sensitive too.

 

[Mr. Self-destruct]

Not the tube. 20 mins on, turned off, used ballpoint pen poked section A and came on. I have no clue. Sad.

 

[Paul Birkeland]

Part of the problem with what I'm seeing here is that when you poke at some connections with a meter and you get a noise, that may not mean anything is actually wrong with the amp.  If you poke at one of the high voltage rectifier diode tabs with a meter probe and get noise out of the amp, that's not abnormal.  The same goes for the choke connections. 

We used to sell the soft-start retrofit for the Paramount that would provide a fresh set of parts and the updated driver board, but that has been discontinued. 

One thing you could do is to switch the C4S boards between amps to see if the problem follows a board or sticks around in one amp chassis despite swapping C4S boards.

 

[Mr. Self-destruct]

Swapped the c4s. Issue followed.

 

[Mr. Self-destruct]

Is there any type of replacement?

 

[Paul Birkeland]

Two of these would give you the boards and a bunch of the parts you'd need:
https://bottlehead.com/product/stereomour-ii-shunt-regulator-upgrade-kit/

If the bosses give the OK, we can send you the soft-start manual so you can source the rest of the bits.

 

[Mr. Self-destruct]

Hi, ok I've replaced both 2n2907a and 2 LEDs on B side. Playing strong fingers crossed.  New leds are like twice as bright. A more pro solder station, magnify light, and 63/37 solder definitely improved my work.