Crack Failure

[lazybill]

I hate to say i'm the first to fail on this project but it ain't lookin' good.  After finishing up the wirering I gave it a resistance check and all seemed fine although 6&7 were higher values than are wanted as were 9& 10 ,they all pegged the meter in the 20k range.  I surveyed the circuit one more time and found a cold solder joint and one connection that was not soldered (slow down Bill) along with a rca jack that looked as though it might be shorted out.  I fixed these and measured again with the same results.   Again I checked the wireing against the guide and couldn,t find any problems.  I put in the fuse turned on the power and nothing, blown fuse.  I have checked the wireing several more times and done new resistance checks and nothing changes.  I searched the forum and saw that maybe a 1 watt fuse instead of the 1/2watt was the answer but that didn't work out.  I continuously check the wireing for a shot but cannot find.  Anyone have a spot to check other wise I'll have to accept my fate and failure.
lazybill

[porcupunctis]

No need to despair this early in the game.  The great thing about Bottlehead gear is that you CAN actually troubleshoot and fix these things.  All you need is patience and an eye for detail.  OK, you might need a DMM as well.

Make sure that it is unplugged and start checking your connections from the power input socket forward through the circuit.  Look for solder lines that are connecting points that shouldn't be (this is rare, if not impossible with terminal strips but very common on the circuit boards).  Look for component leads that are touching where they shouldn't. 

Triple-check the orientation and connections on the diodes. 

Make sure you check out Doc's troubleshooting advice.  http://www.bottlehead.com/smf/index.php/topic,1667.0.html

Stay positive, you'll have this thing off life-support before you know it.

[Grainger49]

I'm with Randall, it can be fixed through the forum.  Check the orientation, striped side placement of the power supply capacitors too.  That is the three big black caps at the back of the chassis.  See that they match to the pictures in the manual.

I'm paging through the manual.  Readings on 6, 7, 9, 10 are the output from the 6080 tube.  Looking at the picture on page 38 of the manual the stripes of those capacitors are toward the outside of the chassis, is that how yours are oriented?

The resistance readings should be about 3000 ohms (+/- 10%) on 7 & 9.  You are reading across those big white resistors that are connected on the other end to terminal 3 (I think it is 3) which is grounded to the plate.  That is, one meter lead on either 7 or 9 and the other touching the top plate it should be 3k ohms.

Similarly the readings on 6 & 8 should be about 2.5k (2500) ohms.  You should be reading across another pair of resistors to ground. 

If not we have a problem here.

Post your readings, what they should be and only post those that are out of spec (outside +/- 15%).

If the 1/2 amp fuse did not blow there is no advantage to going to a 1 amp fuse.  Did the 1/2 amp blow?  Fuses should measure zero on resistance.

[lazybill]

Thank you both for the quick responses.  I've checked the wiring one more time and couldn't find any descrepencies from the manual.  I do have problems on the resistance check however.  On the transformer terminals #1 reads infinite,#2 reads infinite,#'s 4&5 read 0.  Moving to the bottom terminals, 6&9 read 19k+ and 7&10 read 16k+.  All other terminals on board seem to be O.K.  All orientation is according to manual.

[Mr. Davis]

Post some pictures. 

[Grainger49]

Bill,

You mention a resistance range setting in the first post.  Be certain that you change the range so that the maximum is above the resistance to be measured.

After a while you can't find the problem because you have stared at it too long.  Keep that in mind and take a break from it if you need to.

Like I said, it will help us if we can assist you without having to flip through the manual.  To that end post your out of spec measurements, what you get, what it should be and where it is read.  No need to post those that are right.

Unless I missed it, I don't see that the transformer terminals are part of the resistance checkout.  So unless they are tied to some of the terminals that are checked don't worry about them.  I can't ever remember a Bottlehead transformer being bad when new.

Did the capacitor orientation check out?

Did the diode orientation check out?

Do put back in the 1/2 amp fuse if it didn't blow?  Did it blow?

What resistance readings did you get on 6, 7, 9, 10?

[lazybill]

Grainger49
Let it sit overnite an began new checks this morning on the right terminals(not 1-10 on transformer).  First time through everything came out fine. the second time through things changed, hopefully the capacitors had something to do with that.  Terminals 1,2,4,5 all had some minor resistance not the Infinity that was first measured.  After changing ranges downward they began to recede slowly.  The reading on 6,7 &9,10 are all fine.  The capacitor orientation is according to manual as is the diode orientation.  The 1/2 amp fuse was blown more than once(tried again after fixing a couple of bad solder joints) and I tried a slow-blo 1/2 amp and then a 1 amp and both blew.  That's from the latest impasse.
Thanks Bill

[Paul Joppa]

Assuming you have a good stock of fuses (!) it might help to disconnect the circuit from the power transformer.

Look at p.26 in the manual. First, make sure that the secondaries are in the correct phase - red from terminal 6 to terminal 9, and black from terminal 7 to terminal 10 (picture at the top of the page). Then (picture at the bottom of the page) locate the red wire from power transformer terminal 9 to terminal strip lug 20 and disconnect one end of this wire - probably the end at power transformer terminal 9 will be the most convenient.

Now the high voltage power supply is disconnected. Put in a good fuse and try it again. If all is well, the fuse won't blow and the tube heaters will glow. That would mean that the power transformer is good, the transformer input wiring is good, and the filament power wiring is good. Hence any problem will be in the high voltage section - you will have narrowed the field of possibilities considerably. We'll pursue that after we find out if it's the problem.

If the fuse still blows, then disconnect the red wire at power transformer terminal 4, which feeds filament power to the tubes. If another fresh fuse blows, then the primary or the primary wiring is at fault, if not then the heater wiring is at fault. Both of these are quite simple circuits and easy to trace - just wires and switches, no components.

[Grainger49]

Bill,

After you get this fixed you might consider an "autoranging" meter.  I will send you some links to some after we get this fixed.  After it is fixed you will get the "bug."

I think you are right, the capacitors often charge and change the readings.  Terminals 1, 2, 4, 5 and 13 are those noted with a * and will certainly do this.  Whether they go to infinity is a function of your meter.  I will say that your readings are just fine!

It is odd, once the capacitors get charged fully they never blow the 1/2 amp fuse.  I had a similar thing happen when I first started my Eros (new to me a month ago).  At first it used 10 more watts than it uses today.  So once you get it started it will most likely be fine with the 1/2A fuse.

I'm posting a few seconds after Paul Joppa posted so now I'm going over his post.  

I think the verification of the power transformer (PT) secondaries is a big step forward.  

If the fuse blows when the high voltage (B+) is disconnected, then there is a problem in the heater wiring or before the transformer (switch, fuse, IEC connector).  

Paul J has describe all that.

[lazybill]

Paul - First before anything else, thank you.

I removed the wire from terminal 9, inserted tubes into sockets,replaced fuse with 1/2 amp slo-blo and turned on power.  Fuse was blown.  Removed wire from terminal 4 replaced fuse, turned on power, another blown fuse.  I didn't redo terminal 9 or insert tubes.  I can assume the primary circuit is  partially at fault.  There may be more.

Grainger 49 - Yea i'm using a sears special.  I have a new autoranging meter unopened I was going to take back to Fry's I picked up while getting some fuses.  Not enough fuses I  might add. I'm down to two 1/2amp fuses and 3 1amp( if I can use those) It's 60 miles round trip to get more fuses.

[Paul Joppa]

OK - progress indeed!

Measure the resistance of the transformer primary - transformer terminals 1 to 2; it should be about 13 ohms. Then check the resistance from either 1 or 2, to ghassis ground - is should be infinite. Finally, re-check the wiring from those terminals to the power switch and the IEC socket. The error must be somewhere along those paths.

Leave the secondaries disconnected until you fix the primary wiring. Then connect them back, one at a time starting with the heater wiring.

[lazybill]

Paul
Resistance between 1 and 2 is 84 ohms.  Chassis ground to 1 or 2 is infinite.  I've looked at those connections several times and compared with manual pictures and see no deviation.  I guess its possible I may have burned  the iec terminal but it shows no signs of that.

[Doc B.]

Sorry don't have a manual handy today. But one of the first things to check when a fuse blows is if any of the uf4007 rectifiers have blown.

[Paul Joppa]

Paul
Resistance between 1 and 2 is 84 ohms.  Chassis ground to 1 or 2 is infinite.  I've looked at those connections several times and compared with manual pictures and see no deviation.  I guess its possible I may have burned  the iec terminal but it shows no signs of that.

Bingo!

The transformer is in backwards. There are terminal numbers embossed on the bobbin, which are repeated on the label. You can check to see if the label was correctly applied, or if the transformer was wound with an upside down bobbin.

Remove all the connections to the transformer and remove the transformer from the chassis. On the work bench, rotate it 180 degrees so that it is in the correct orientation. Then check winding resistances to see if there is any damage:

Terminals 1-2 (formerly 9-10) should be 13 ohms

Terminals 4-5 (formerly 6-7) should be very low, less than an ohm

Terminals 6-7 (formerly 4-5) should be 84 ohms

Terminal 9-10 (formerly 1-2) should be 84 ohms

Then confirm that none of the four windings are connected to any of the others or to the core. This is kind of laborious, and I don't anticipate any problems, but let's be sure before re-installing the transformer!

If it's good, then remove and rotate the label so that it identifies the terminals correctly. If the embossed terminal numbers are incorrect, send us an email so we can trace the problem, hopefully to a particular batch of transformers, and so we can alert our supplier to the error, and prevent it happening again.

Now you can re-install the transformer and re-connect the wires.

It's probably a good idea to check the heater resistances of the tubes before firing it up, since what caused the fuse to blow was applying 160 volts to the 6-volt heaters (!) That would be pin 7 to pin 8 on the 6080, pin 9 to pin 4 and pin 9 to pin 5 on the 12AU7. I don't expect a problem, but again, let's be sure first.

[lazybill]

Paul
Just walked in from getting more fuses to see your note.  When I was first doing the resistance checks and using the transformer terminals by mistake I did indeed notice the the label did not match the markings on the tabs.  The label has 6-10 but the tabs are marked 5-1 just from a first glance.  Anyway we will check it out.  Just checked the tabs and they match what they should be in reverse.  I think its a yea!  Must be Murphy"s law.  Please fill me in on checking the windings.