@RichBC

These are the only images that I have of the C1 hash board.

I have not measured the core voltage directly with a DVM.

Are you sure you are looking in the correct location?
Do you have a schematic of the board or are you just using the ASIC device data sheet?

After you Modify voltage, you do a Save&Apply, then need to Power off and Restart the miner, right?

The C1 hashing boards are S3 family boards.

So, yes - they are capable of changing the voltage.

I have a C1 Batch 1 and a C1 Batch 2.


The best settings for Under-volting/Under-clocking were suggested by another user:

0675/200      530W      803Ghs      0.66W/Ghs

0760/250      790W       1008Ghs       0.783W/Ghs

I set mine to 803GHs now because it's summer here and heat is an issue.
In the winter, 1008GHs.

Hope this helps

Ask Bitmain if you can send a C1 miner in for repair.

(Let them worry about where to find you a new one, if needed, or repair yours.)


BTW
I tried to purchase that controller card from them last year, that was the one C1 component that
they wouldn't let me purchase ... probably for proprietary reasons.

I was going to convert my 2x S3s into a C1 but, I couldn't without that controller.

You said:

Falling hashrate problem with a C1.  It has been running at intentionally lower frequency to baby it.  Should be running at 960GH/s@243.5M and after a cold start it does but drops to 850GH/s after a few hours.  Up last night I restarted due to 850GH/s hashrate.  

  If this isn't it then it's an ASIC that heats and accumulates errors (an internal board) but even when the hashboard isn't drawing much current while the other three are, there are no x's in any chain.
--------------------------------------------------------------------------------------------------------------------------------------------


Let it run at the lower 850GH/s hashrate for a day or so, you should see X's appear on one of the chains..

Just to rule out other possible causes:
Have you swapped Power Supplies with a different (working) C1?
Have you swapped the Pump/radiator/cooling setup with a working C1?
Ambient temperature?




More than likely it's a cooling problem if it happens after it has ran for several hours IMO

I had a similar problem, at stock settings - 250M/0760 volts (hash rate should be 1008 GH/s, would drop to ~930 GH/s)
to correct this, I had to replace the cooling block used on chain #2



I now run both of mine at 200M /0675 Volts - gives me 805 GH/s each
-due to heat concerns. They are both stable now having run for 29 days
without touching them

Batch 4?

C2 (with the higher density chips) ?

Right, the cables would be a consideration.

Also, some earlier revision S3 boards have the data cable connector mounted
on the back side of the board.

The C1 boards are delivered with ribbon connectors all on the component side of the board.
Makes it easier to plug in ribbon cable if you have back to back boards mounted on a water block situation.

It's possible to twist the cable and squeeze it in between two boards on a C1 if you
have an older rev hashing board.. if, the cable will reach.

You can buy the Water blocks..
http://shop.syscooling.com/goods.php?id=47

but, remember the C1 also has the Air Cooled Heatsinks
email syscooling, I bet they make those also..

The top of page 72
Post # 1421

He meant 0.66W/GHs

I've had good luck with this coolant:
http://www.frozencpu.com/products/17472/ex-liq-262/XSPC_EC6_High_Performance_Liquid_Cooling_Premix_Coolant_-_1L_-_UV_Green.html

 
If you did not receive a coupon and you’d like to purchase a miner with a coupon, please do not hesitate and send an email to info@bitmaintech.com in the below format. We will manually assign the coupon to your account. You can only use one coupon per miner.
 
Email Subject: Please assign the coupons to my account
User ID (the account in bitmaintech.com): 
Coupon Type (S3+, S4 and C1):
Quantity

In my case it was the water block.

..Try the thermal paste first

My Notes from the teardown of my C1 Miner


1. Be aware that the cooling blocks (that nearly all screws in the C1 attach to)
are made of extremely soft aluminum. Very easy to strip.

2. Use only a LIGHT 2-finger torque on all of the screws.

3. The 4 Spring loaded screws that attach the Air cooled side heatsinks (fins)
were by far the hardest to get right. Extreme care should be taken with these screws
Very light touch using a good screwdriver. The heads on these screws are also easy
to strip out. LIGHT touch.

Do not over tighten these 4 screws, I believe these 4 screws are capable of bottoming out
in their screw threads in the cooling block

4. When reassembling, compare the Air cooled fins position (or orientation)
to one of the other hashing boards. You can use vias or one of the components on the board
to eyeball the position of the heatsink. These Air cooled heatsinks float on the top
of the ASIC chips, hence the Springs to keep the force.

5. Once installed, you can compare the Spring action (tension) between two or more
of the hashing boards. You can rock the board up a bit (1mm) if you reach your fingertips
underneath the top of the heatsink. This is only to compare the tension between
two different heatsinks. You don't have to do this.

6. Also, do not tighten with any force the Cooling block coolant connections as
they will sheer off completely if too much force is used (soft aluminum).

7. The Cooling blocks are available from the SysCooling web site.

http://shop.syscooling.com/goods.php?id=47

8. Reapply thermal paste on the ASIC chips

If it happens after a few hours, it is a cooling problem.

I had to replace the cooling block to fix my very similar problem.

I had 5 Xs on the 2nd chain hash board after a couple of hours.

Can you post a screen shot of the miner status page?
(that would be helpful - use tinypic.com)

What is your ambient temperature like?

So, you are running it at 250M freq. and 0760 Volts?

Thanks for posting this.

What is the firmware date that you are using now?

@BitmainWarranty

How about passing this on to the engineers while you are at it:

On the S3+s, I can reboot them from the software GUI, without issue.

On the C1s, if I reboot (GUI) they do not come back up cleanly, you have to reset the power switch.


When I say they don't come back up cleanly, I mean the hash rate does not return to the
1000GH/s. Maybe 760 GH/s

Often times the ASICs on chain #2 or chain #3 hashing boards come up all --s or ..s

ssh password admin on C1

Anyone try the new C1 firmware on the Bitmain site yet?

Interesting that the date on it is almost 3 months old...