Hardware problem

This Forum is about the Opentherm gateway (OTG) from Schelte

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Hardware problem

Postby mvroosmalen » Sun Aug 14, 2016 1:30 pm

Hi,

Just constructed the OTGW and started with the diagnostics part (http://otgw.tclcode.com/debugging.html#power) to be sure everything is correct. The first check:
Check for 5V +/- 1% between pins 5 and 14 of IC1 and pin 15 and 16 of IC2

measures around 6.5V which is well above the set specs. Can someone help me out how to proceed?

Thanks,

Mark
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Re: Hardware problem

Postby hvxl » Sun Aug 14, 2016 7:50 pm

The usual reason for a wrong Vcc is using the wrong voltage regulator, an LM78L05 (to-92) instead of an LM7805 (to-220). Otherwise the LM7805 may be bad or getting an input voltage that is too high (wrong transformer).
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Re: Hardware problem

Postby mvroosmalen » Fri Aug 19, 2016 6:52 pm

Just checked and its a L7805CV, is this one correct?
https://goo.gl/photos/iWcormaCAdZPLady5

How can I check the input Vcc?

Thanks Mark
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Re: Hardware problem

Postby hvxl » Sat Aug 20, 2016 10:19 pm

Unfortunately the datasheets are not very clear on what the maximum input voltage is at which the device will still work as advertised. Usually the TO220 versions work up to 25V, while the TO92 versions may start misbehaving at a little over 20V. Yours is a TO220, so that is probably OK.

The easiest access to the input voltage is around D1-D4. Measure between the opposite ends of D1 or D2 and D3 or D4.
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Re: Hardware problem

Postby mvroosmalen » Sun Aug 21, 2016 8:20 pm

Thanks will try that, meanwhile a replacement part is being shipped hoping it resolves this problem. When it arrives I'll also check to VCC.

Mark
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Re: Hardware problem

Postby mvroosmalen » Sat Aug 27, 2016 5:14 pm

Hi

Just received the new L7805CV and before installing I confirmed the VCC (21.1V) which should be OK. Installation of the new L7805CV improved the VCC on pin 15 and 16 of IC2 (5.03V). Next I tested Delay symmetry with loop between boiler en thermo and found this:
OK1A high-to-low: 12us
OK1A low-to-high: 26us
OK1B high-to-low: ### Error
OK1B low-to-high: ### Error

This seems not OK. Can you help me through next logical steps to resolve the none working hardware?

Thanks Mark
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Re: Hardware problem

Postby hvxl » Mon Aug 29, 2016 4:39 pm

Indeed that looks like there is a hardware fault. Check the troubleshooting instructions on how to investigate this.
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Re: Hardware problem

Postby mvroosmalen » Tue Aug 30, 2016 7:08 pm

I checked everything indicate in the trouble shooting and V and A are within range. The last remark was testing #4 which I posted earlier. There is no signal on the Master interface..... Did I miss anything here?
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Re: Hardware problem

Postby hvxl » Wed Aug 31, 2016 5:01 pm

So you claim that you performed all tests mentioned under "Opentherm interfaces" and they all passed. I'm specifically interested in:
  • "If the voltage is correct you can measure the current between the two terminals of X1. It should be between 5mA and 9mA"
  • "If you connect pin 3 of the IC1 socket to ground (e.g. pin 5), the current between the two terminals of X1 should be between 17mA and 23mA."
  • "Measure the voltage on pin 18 of the IC1 socket with pin 3 left open and again when it is connected to ground. In the former case the voltage should be below 1.25V (it is actually expected to be 0V). In the latter case the voltage must be above 1.25V (and will probably be close to 5V)."
Diagnostics test #4 does pretty much the same thing as that last test, but also measures the time it takes for the level to change. You get an error result if it takes more than 65ms to switch. That's nearly an eternity for electronics. If it takes that long, but finally reaches the desired level, there must be some unwanted capacity somewhere.
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Re: Hardware problem

Postby mvroosmalen » Fri Sep 02, 2016 7:28 pm

Just checked the mA over the different contacts:
"If the voltage is correct you can measure the current between the two terminals of X1. It should be between 5mA and 9mA"
The current is 6.25mA

"If you connect pin 3 of the IC1 socket to ground (e.g. pin 5), the current between the two terminals of X1 should be between 17mA and 23mA."
The current is 20.2mA

"Measure the voltage on pin 18 of the IC1 socket with pin 3 left open and again when it is connected to ground. In the former case the voltage should be below 1.25V (it is actually expected to be 0V). In the latter case the voltage must be above 1.25V (and will probably be close to 5V)."
in both cases I measure 0V??<--- seems not OK now?? miscounted :D but after recounting and re-measurement I got 0V and 2.10V between ground and 18..

Thanks for the help so far, what's the next step?

Mark
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Re: Hardware problem

Postby hvxl » Sun Sep 04, 2016 10:33 am

That looks good. Have you tried if it works?
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Re: Hardware problem

Postby mvroosmalen » Mon Sep 05, 2016 6:18 pm

mmmm..
Enter test number: 4
OK1A high-to-low: 10us
OK1A low-to-high: 24us
OK1B high-to-low: ### Error
OK1B low-to-high: ### Error

still not OK?
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Re: Hardware problem

Postby hvxl » Wed Sep 07, 2016 8:13 pm

That does look like there is a problem with the opto-coupler. But once again, have you tried if it works? If you don't want to load the gateway firmware, you can try running diagnostics test #2 and #3.
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Re: Hardware problem

Postby mvroosmalen » Sun Sep 18, 2016 5:50 pm

Hi,

just found some time to test the OTGW as you proposed and started test #2 and #3. With both nothing happens (nothing in log or reported on the screen) :-(
Maybe also worthwhile, the thermostat went black... only after connecting the thermostat to the boiler/CV it displayed the temp etc.

Hope this helps to focus on the problem..

Thanks for the support so far.

Mark
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Re: Hardware problem

Postby hvxl » Fri Sep 30, 2016 9:08 pm

The tests you performed over time produced conflicting results. Possibly there is a loose connection somewhere. Let's first focus on the thermostat. With all components of the OTGW installed but no thermostat or boiler connected, measure the voltage on X1. It should be 24V, or thereabout. Next measure the current. Expect 5-9 mA. Then connect the thermostat and measure the voltage on X1 again. You may see some instability about once per second, but the rest of the time the voltage should have dropped below 8V. If that is the case, run test #2 again. It should report something. If so, proceed from there (connect the boiler and run test #3). If not, check for bad contacts in the slave interface part of the OTGW.

Note: Some thermostats don't show anything until they received a first response. So a black screen does not immediately mean a problem on the thermostat connection.
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