Eros BUILD HELP NEEDED

[haiku626]

Hello Everyone,
First of all I would like to say that I love the Bottlehead sound.  Thus far I have built the wonderful Crack and its Speedball upgrade.  Recently I embarked on an Eros but have run into some problems when doing resistance and voltage checks.  I will admit that I am one of those builders that basically just knows which end of the soldering iron gets hot...  Thank you in advance to all who can help me.

Resistance readings out of sync: first # is actual / second # is standard
Terminals
T11: 47 / 0
T12: 121 / 60
T13: 37 / 0
T14: 132 / 71
T15: 47 / 0
Nine pin sockets
B1: 72 /27
B6: 121 / 60
C7: 121 / 60
 
Voltage readings out of sync:
C4S board right side (B)
bA: 164 / 0
Kreg: 166 / 1
OB: 221 / 100
breg: 218 / 100
On power up 2 of the leds on this side light up but soon fade out

Thank You

[Grainger49]

Haiku,

At least you know which end of the soldering iron to grab and which not to grab.  You should be fine.

Can you edit (called modify in the top right of your post) and add the expected values for the points you are out of spec with?  That will keep us from jumping back and fourth in the manual.

Looking at the schematic says that bA for either channel should be grounded.  With it at 164V that says the wire attached is not grounded.  Check the solder joints on each end.  Use your meter set to the lowest resistance range and measure from bA to the chassis plate then from the terminal (either T1 or T15) to the chassis plate.  Both readings should be almost the same as when you touch the meter leads together, usually about 0.1 or 0.2 ohms.

I can't find Kreg on the schematic I have so I'll go upstairs and do some checking.

Ob should be at 100V.  It is high because the tube isn't on.  So I'll check on this as well.

Which LEDs come on?  Is it the two on the A side or the two on the B side?  I bet A side.

[haiku626]

Hi Grainger,
Thank you very much for the correct diagnosis of not having the proper ground.  I found that I mistakenly attached the wire from T11 to T27 when it should have been T26.   Man, my old eyes are playing tricks on me...   Fixing this problem placed my previous mentioned resistance issues more or less in sync with the expected values.

Of course I was now really excited and anxious to spin some vinyl, but did a voltage check just to be sure.
This time all readings on the B CS4 board were okay except for OA which gave a reading of 99 vs an expected value of 170 and Kreg which gave a reading of .59 vs 1.00.  I noticed all LEDs light up on this CS4 but the two on the B side were delayed in doing so when compared to the other boards.

Anyway I tried to listen to some music with the Eros regardless of the out of sync reading of OA and Kreg.  To my disappointment, no sound out of the left channel.  Oh well I should have expected it.  Hopefully you or someone else with expertise can help me.

[Grainger49]

Haiku, I'm 62, my eyes play the same tricks on me.  I spent yesterday, on and off, getting LEDs (diodes) in 4 C4S boards in the right direction.

Some LEDs come on after others.  It has to do with where in the circuit they are and how quickly the heater on the tube warms up.  As long as they are all on, that is good.

So... opening the Eros schematic...  assuming that it is the Kreg on the left channel, there is a lot in that circuit.

You will need to look closely at this board.  Check these components for orientation and that it is the right value.  The transistor leads can be a pain.

2200uF@4V, small silver cap
2N222 transistor, again small, silver, near that cap
27k ohm 1W resistor
174 ohm resistor

The two above resistors turn on the transistor.  If they are swapped it won't come on and the EF86 won't turn on.

[haiku626]

Hi Grainger,
All of the resistor values check out to expected value, the 2N222 transistor and 2700uf capacitor are oriented properly.  I am thinking that the EF86 tube does go on since there is some warmth to it when touched after it is left on for a few minutes.

[Paul Joppa]

Check the tube pin voltages. The low voltage at kreg suggests the servo is trying to lower the EF86 plate voltage (should be 100v at pin 6) so either there's a wiring error or possibly the EF86 is not conducting well. The voltage check is the best way to determine where the problem is, but you can swap EF86s to see if the problem moves, and if the tube is warm you can let it run for a while to see if the emission kicks in.

[Grainger49]

D'oh!  (https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi244.photobucket.com%2Falbums%2Fgg7%2FGrainger49%2FSmiles%2FSlapHead.gif&hash=e5c580c3cfdf525c26703ae0328aefb586b04de5)

Swapping tubes is always the first and easiest idea.  See if the problem follows the EF86 when you swap them.

[haiku626]

Swapped the tubes between A and B; however, the problem remained at B.  Shucks, I was really hoping that it would be a tube problem...
Kreg: .05VDC / s/b 1
OA: 101VDC / s/b 170
Pin B6 voltage checked out at 102.6
I rewetted some of the soldering where I thought it may help but no luck in improving the readings.

[Noskipallwd]

It's pretty easy to create solder bridges between the small pads on these boards, done it myself a couple of times. It wouldn't hurt to re-inspect the boards for these.

Cheers,
Shawn

[haiku626]

There may be a solder bridge between the two -reg connections closest to the long edge of the board with the LG 2700 and black wire.  Does this matter?

[Grainger49]

If they are both -reg, they are all supposed to be connected by the trace on the PCB.  But the problem comes when adjacent outputs get bridged.

Did you check the component values listed above?  Those are in the Kreg circuit.  Then verify that R1 on the A side of this board is indeed 113 ohms.  That sets the current for the C⁴S feeding OA.

And don't feel alone, I'm having fits with 11 year old boards I decided to install on Tuesday.  It is posted in the Legacy folder.

[haiku626]

Hi Grainger,
Thanks for comforting me.  Without the support from the Forum members I think I would be getting a nervous breakdown.  Everyone's help has been much appreciated. 
I will check the R1 value when I get home from work.  I live in a different time zone so you'll see my reply Fri morning.

[haiku626]

I verified my visual inspection of the closely soldered connections for unwanted bridges with my meter especially with the transistors and did not find a problem.
All of the component values for R1 A and B, R2 A and B, R3, and R4 were found to be within their expected values.  Pin B6 voltage also checked out okay at 101.4
I rechecked the orientation of the capacitors and transistors along with the correct positioning of the leads.
Kreg still at .059 s/b 1.0
OA at 100.6 s/b 170
Should I try running the amp for a few hours to see if something kicks in or will I be wasting my effort?  I have never had it powered up for more than 15 minutes since the tube swapping did not move the problem to the other side.

[Grainger49]

Since OA is not up to voltage the cathode voltage, Kreg, would follow.  I should have spotted this earlier, sorry.

I'm printing out the schematics now. 

I think the two LEDs that glow and turn off are in that OA circuit.  The transistors are not turning on properly so they are not passing the voltage to OA.  Look at the picture on the bottom of page 29 of the manual.  Verify the resistance of R1, 113 ohms, the resistance of R2A, 120K, and that you didn't swap the two transistors (not likely because of the shapes) in this circuit.  There are only 6 circuit elements and the LEDs glow so the other four are left. 

I will add to this post knowing you are going to troubleshoot later.

[Paul Joppa]

The center tube (socket C) voltages would help. Inspect the wiring while there, especially whether C6 and C7 may be shorted to each other. B6 goes to C7 (assuming I have identified the parts correctly) and OA to C6, and unless there is a short I can't see how they might have the same voltage.