Build Log: A Physician hooked on Crack (My very first DIY project)

[Grainger49]

Ok, your picture verifies two caps and the existence of the 270k ohm resistor. 

Terminals B3, B6, 7 and 9 are good.

One plate resistor is clearly soldered well but the other one looks to be one ohm. 

I am wondering about the grounds throughout the circuit.  What point are you using to measure your resistances to?  That is, the meter lead you do not move.

Here is the ground circuit from another thread:

The start of the grounding points is terminal 3.  This jumps to the 2 left lugs of the volume pot and to the back of the chassis from there to the RCA jacks.  From the top left lug of the volume pot there is a grounding jumper to the two bottom lugs of the headphone jack.  This jack may be different than what is being delivered today.

Also from terminal 3 you go to the center lug of the 9 pin tube socket.  This is the ground route for the LEDs in the cathode circuits of the 12AU7s.

The power supply ground comes from those bottom headphone jack terminals to terminal 12.  From there it jumpers to terminal 14 and ends at terminal 20.

The heater (AC) supply is a ground wire from transformer terminal 4 to terminal 22.

Ok, so all this means you should clip on to the chassis (which is screwed to terminal 3 the source of all the grounds).  Tracing from the plate outward you should read zero to T3, Volume 2 left lugs, both RCA outer conductors, headphone jack bottom terminals, T12, T14, T20, center pin of the 9 pin socket, and to T22.

Other grounds that should be solid are pin 8 of the large tube, pin 4 and 5 of the small tube, T8, T11, T14, T16, T17, T20, T21 & T22.

So, clip one meter lead onto the top plate.  Then trace the circuit with your other meter lead starting with terminal 3.  You should read zero or what you have determined as zero for your meter at all points.  A fraction of an ohm is good. 

Finally a couple of questions, do you have an analog meter or digital?  Does it autorange?

[sanadsaad]

Alright so I did a full recheck and turns out the leads in terminal 3 were inserted but not soldered. Mustve been missed during the early hours. Soldering those and reheating the 7 and 9 terminals which I suspected were bad, here's the final resistance checks that now differ from the manual:

Terminal 1: 22.6k/*
Terminal 2: 0.5k/*
Terminal 4: 0.5k/*
Terminal 5: 22.6k/*
Terminal 13: 0.5k and does not climb/* slowly climbing to 270k

I was using terminal 12 and readings are the same when I test from the chassis plate. And my multimeter is a digital one. Here's the link:
http://www.uni-trend.com/ut33c.html

[Laudanum]

1, 2, 4, 5 and 13 are listed with an * because, from the manual ...  "The values signified with a * are going to vary from ohmmeter to ohmmeter because these terminals are connected to the filter capacitors, which try to charge themselves off the battery in the meter, causing a fluctuating reading. If the circuit is connected properly these readings will wander in the tens or hundreds of Kohms or higher range. What you want to watch out for is a zero reading at one of these terminals, which would indicate that something is mis-wired."

You may very well be ok but Grainger or one of the more tech savvy will chime in to confirm or assist further.

[sanadsaad]

Desmond the readings look fine to me except for the terminal 13 reading not rising. If the experts say it's fine, i'm raring to go onto the voltage testing! I just realized I havent been given the fuse or the IEC power cord with my kit. Oh well. Might as well run to the store now while I wait for the go ahead. It's a 5A fuse right? Thats what it says on the parts list. I have a 10A fuse sittin on my desk but I guess that wouldnt do.

[Laudanum]

Doc suggested a 1 amp slo-blo in another thread.  Mine shipped with a 1 amp as well.  I think there were too many fuses nuisance blowing with the .5 amp but was never changed in the manual.  Go with a 1 amp.  I believe it is a 20mm fuse.

[Grainger49]

Looking at your meter it is a digital that needs the scale selected, not autoranging.

Whether the reading rises might be a function of your meter.  First try directly across one of the capacitors.  The reading typically rises across a capacitor.  A good one to try is the first one across terminals 20 and 21.  This is a good one to test for a rising resistance.  Then swap the leads the resistance should show a negative value dropping.

[Laudanum]

Just noticed that you've typed 5 amp fuse.  You may have edited your post while I was typing my response yesterday or I may have just misread.  Reagrdless, the manual states a .5 amp (0.5, 1/2 amp fuse)  NOT 5 amp.  Atleast my manual does.   Again, Doc B recommended a 1 amp slo-blow fuse in a post on this board.   But dont use a 5 or 10 amp.  Make sure it's .5 or 1 amp fuse ... preferably 1 amp slo-blow.  

[Grainger49]

Ok, going back to the start of the resistance checkouts:

Terminals 7 and 9 (B3 & B6) are no longer zero ohms to ground, right?  The solder joint should have fixed it.

Your last readings indicate that terminal 13 is 500 ohms to ground, which you read.  So terminals 1 and 5 wired back to terminal 13 through the 22k1 plate resistors check all the way to terminal 13 (22k1 +500= 22k6).  Let's say that the lack of a climbing resistance reading is a function of you meter.  At this point every reading you have that is not right is a "climbing" reading. 

It may be the time for the smoke test (stock fuse if you don't have a 1 amp slow blow).  I know you don't have spare parts available close to where you are, but at some point you are going to have to turn the Crack on.  Cross your fingers and turn it on and off very quickly, as fast as you can.  Trust me this has a function. 

Then turn it on with it upside down (best to have it on and plug it in), have one of your meter leads clipped so you can start taking voltage readings.

Pray for no smoke.  Post back.

[sanadsaad]

Tried the terminal 20 and 21 resistance check. Reading is 0. Tried to start the crack twice with a 1A regular fuse(cant find slo-blo in the market). Blew up twice. I found the following replacements in the market:

-the uf4007s
-270 ohm 5W wirewound resistors
-3K ohm 10W wirewound resistors
--All the electrolytic caps

Cant find the metal film resistors anywhere though.

[Grainger49]

Are you saying that the whole power supply blew up?

Everything you list will work just like the original.  The 10W resistors will be larger than the ones you have, believe it or not.  How did you determine that those needed replacing.  They are not in the power supply.  Maybe they got tied to the power supply somehow?

We have to solve the problem with the power supply first.  There was a short in the high voltage to take all this out.

I don't know if you need film resistors yet.

[sanadsaad]

Oh no no. The fuse blew up. I went to a shop to get the fuse and checked if they have any replacement parts in case they blow up later. The shops here close for 8 days on account of Eid so I wouldnt be able to get anything if I needed em. So lets start the troubleshooting. Im going over all the wires again according to the manual to see if I missed anything.

[Paul Joppa]

While you are checking things, make sure of the orientation of the diodes and capacitors. This is fairly often the cause of blown fuses. Check the orientation of the sockets as well - the octal has a slot for the pin on the tube bass, and the sockets have been known to get installed 180 degrees out. Finally, make sure wires go to the correct terminal - that's another common mistake, and especially hard to see after you make the initial mistake.

[Grainger49]

Tried the terminal 20 and 21 resistance check. Reading is 0.  .  .  .  

This is wrong, the capacitor should be a high resistance to ground, terminal 20.  Does terminal 20 read near zero resistance to the top plate?  If the capacitor is internally shorted you get zero ohms and the fuse blows.  But I don't think this is the problem because you got a zero reading before applying the power.  A bad capacitor often, not always, has a domed end.  Ends of these power supply caps should be flat.  If not, they are bad.  

But my next suggestion is a little harder.  Remove one cap from the power supply and measure it.  Regardless of whose meter it is you should get a high reading not a low reading.

[sanadsaad]

The caps are all flat. One thing I should mention again. There was a revision in my manual advising me to connect a black wire from terminal 4 to terminal 14U instead of 22U. Im desoldering the terminal 20-21 cap right now. will post soon as tht's done.

[Laudanum]

That revision to connect from transformer terminal 4 to 14U instead of 22L is a possible solution for quieter operation of the amp.  It isnt your problem unless ... the solder joints are bad.