Eros voltage reading problem

[Steve Reese]

I'm on step where you install the 12BH7 in order the measture the voltage from D1 and D6. At first I didn't get anything, and this morning I resoldered all red wires and the two large resistors on top of the board that are twisted together since they had some dark matter in them somehow... one even had came apart somehow. Retouched it and tried again, and wow, I got the 225V... the 4 diodes were glowing and the tube was glowing. I turned it off, unpluged the power cord, switched to red clip to the wire attached to D6, and now it stays steady between 330 to 335. I've retouched D6 and D4, and some more connections... I don't know what else to try. If anyone has any suggestions, I'd greatly appreciate it. Thanks to all who may reply.

 

[Paul Joppa]

You did not say, but I guess you got the 225v at D1 at first, then failed to get it at D6. Am I correct? If so, that indicates one channel's regulator is working and the other isn't.

Measure voltages on the 12BH7 socket pins 1-2-3-6-7-8. That will tell us what the tube is doing, and might lead to where the problem is.

Incidentally, you said "...switched to red clip to the wire attached to D6" - be aware that wires are only attached if the solder connection is good, and it is sometimes necessary to measure at the actual socket lug instead of the wire that appears to be attached to that lug. I only stress this point because such a large proportion of wiring problems end up being solder joints that appear good but aren't.

 

[Steve Reese]

Sorry it took me so long... had family obligations. Here are the measurements:
D1 - 352
D2 - 0
D3 - 0
D4 - 0
D5 - 0
D6 - 352
D7 - 0
D8 - 1

at the 270 ohm it's 352: at the 6.3V both red and black are 0. It's strange how all of the of the voltages were spot on, then only to switch wires, I powered off, switched to D6, and then nothing was right, or as it is now. Here is the problem I had early on in the construction  http://www.bottlehead.com/smf/index.php/topic,3671.0.html

 

[Paul Joppa]

Looks like neither triode is conducting. My first guess is that the heater are not getting any voltage. You should be now have confirmed that the 6.5v heater power is being generated, so look to see if there is an orange glow inside the tube, and if not look at the wiring to tube pins 4/5 and 9.

 

[Steve Reese]

Okay, I will, thanks Paul... I'll post after I check them out.

 

[Steve Reese]

Okay... I basically rebuilt D tube socket and reattached the shunt regulator board, and I'm still getting a reading of around 330V. When I first turn ON, it will hover around 300, then it slowly goes up to 300V. Is there any readings I can take on the board to see what might be the problem?

 

[Paul Birkeland]

Do you have orange tube glow?  (For that matter, is the 12BH7 in the socket?)

 

[Steve Reese]

yes, the tube is in the socket, but has no glow... I'm wondering if the pins are spread too wide or something. It does go into the socket pretty easily.

 

[Paul Birkeland]

This is good information.  There is a shielded twisted pair wire that goes to pins 4/5 and pin 9 on that socket, they feed the voltage that lights the tube.

On the power supply board, there is a pair of pads that say 6.3VDC + -, can you measure the voltage at those pins?

If you have 6.3V there, there should be 6.3V at the tube socket.

If you don't, let us know what you do have at those pads.

Any other messing around with the C4S board at the tube socket is a waste of time until this is sorted out.

-PB

 

[Steve Reese]

Sorry it's taking me so long to get back.... i'm in the beginning stages at work with a company wide computer hardware refresh, so my evenings are taken with that and home duties. I just tested at the 6.5V, and it had nothing. At D1, it was 335V.

 

[Paul Birkeland]

Ok, if there is nothing at the 6.5, there is an error in the components on the power supply board, or there is no AC going to the low voltage supply on the PC board.

The MJE5731A and the LT-1085 chips look the same, can you be sure it's the 1085 that you have soldered to the board and connected to the heatsink?

Also, measure the AC voltage coming into the board between the pads T4/T5.

-PB

 

[Steve Reese]

The chip mounted to the huge heat sink is the LT1085, and T4 & T5 are both 5V which make no sense since they were both tested at 9.7V when it's ask to measure them on pg 42 of the instructions.

 

[Paul Joppa]

Measure the AC voltage between T4 and T5, not the voltage between each of them and ground.

 

[Steve Reese]

Both T4 AND 5 read roughly 2.5 VAC. That's with meter ground mounted to #23 ground and reading T4 and T5 individually.

 

[Paul Birkeland]

Put the black probe on T4 of the PCB, put your red probe on T5 of the PCB, then measure AC voltage.

 

[Steve Reese]

It reads 7

 

[Paul Birkeland]

Ok, next, double check all the 1N5820 diodes and their orientation.  With 7V AC in, the DC voltage coming out will certainly be greater than 0.

After that, set your meter to DC and put the black probe back on ground, then measure the DC voltage present at the banded end of one of the 1N5820 diodes that's closes to the 6.3vDC pads.  This will tell you your DC voltage available to the regulator.

-PB

 

[Steve Reese]

It reads 9V

 

[Paul Birkeland]

OK, so far this is a good sign, you have the AC coming in, you're making into DC (and enough DC at that), but you have no output from the regulator.

The next step is to triple check the two resistors that nestle up to the 1085 regulator, as they set the regulator voltage.

I would also flip the PCB over and touch up the seven solder joints (2 on each resistor, three on the 1085).

Additionally, the two yellow capacitors on the outside of the PC board are polarized, it's possible that one is in backwards.

 

[Steve Reese]

I touched up the 7 resistors and check and verified that the two outer yellow resistors are oriented correctly. Did a voltage check and still no light on Tube or diodes.