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  1. #1

    This is not a DIY post!

    This is not a DIY post! But I may not be able to get an answer here anyway.

    I work for a company that does electronic repair work. We fix computers, GPS, cellphones and so on, to the component level. I spend much of my workday soldering under a microscope. My boss has gotten access to a large quantity of Alerton HVAC modules which have been taken out of service for various reasons. I've been given the job of sorting through them and fixing them as necessary so that they can be put back on the market for sale to contractors (like you guys!).

    For example, one of the modules was a TX-653P. There was a tag on this module that said "analog?". I googled up a program called "TDS" that allowed me to talk to this module over a PC serial port. I hooked up a 24vac transformer and a PC, and was able to exercise all the inputs and outputs of the module. The analog outputs did not work. I isolated the problem to an opamp, changed the opamp, and now the analog outputs work. The module went back to the people we got it from, and they tested it in a real system and verified that it works correctly.

    I have other modules here; dozens of different kinds. I'm not an HVAC guy, I'm an electronics guy. I can dummy up any kind of input signal these things might want, and I can test the outputs. But I need to know how to talk to them, what inputs they expect, and what outputs they produce.

    If I can get this info, I can start repairing modules and my boss will love me. But (no surprise) this information is not easy to get ahold of...

    I have no interest in building my own HVAC setup, or fixing somebody else's. Neither does my company. But I realize that the kinds of questions I have might fall pretty squarely in the "DIY" category. My first question is, can anyone here help me find the low-level info I need to test and repair this hardware? If not, can you bend the rules enough to point me to a place where I _can_ get those questions answered?

  2. #2
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    I used to do electronic hobby building and trouble shooting but that was with old TTL ICs and components that hadn't been shrunk to the size of a grain of rice.

    Back when a IC 555 was the size of a pinky nail. All that said I think that is a PLC.

    Analog outputs would typically be 4 to 20 ma or 2-10 vdc.

    I didnt realize board level component replacement was practical let alone lucrative.

  3. #3
    I didnt realize board level component replacement was practical let alone lucrative
    The TX653 is going for $ and up on ebay etc. An LM324 costs less than a quarter & takes a couple of minutes to swap out. So it still makes sense to do these kind of repairs.

    I also have a bunch of "Microset" boxes which use a 3-wire interface. Looking at the PCB there's really not much there except for shift registers and another LM324... Is there any documentation of the protocol the Microsets speak?

    I have been able to talk to an Ibex module successfully through its RS232 port, but not all modules have RS232 so I'm going to have to use the "comm trunk" which I presume is RS485, right? Hopefully the 485 port speaks the same language as the 232 port.

    I've not had such good luck talking to BACnet modules. I have a BCM-PWS and BCM-ETH and I've been able to talk over TCP/IP to the BCM-ETH but not any further than that. Any advice on exercising BACnet modules (preferably without buying $4k of building management software :-) ?
    Last edited by beenthere; 06-06-2012 at 05:52 AM. Reason: price

  4. #4
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    Quote Originally Posted by Ghlavenka View Post
    The TX653 is going for $ and up on ebay etc. An LM324 costs less than a quarter & takes a couple of minutes to swap out. So it still makes sense to do these kind of repairs.

    I also have a bunch of "Microset" boxes which use a 3-wire interface. Looking at the PCB there's really not much there except for shift registers and another LM324... Is there any documentation of the protocol the Microsets speak?

    I have been able to talk to an Ibex module successfully through its RS232 port, but not all modules have RS232 so I'm going to have to use the "comm trunk" which I presume is RS485, right? Hopefully the 485 port speaks the same language as the 232 port.

    I've not had such good luck talking to BACnet modules. I have a BCM-PWS and BCM-ETH and I've been able to talk over TCP/IP to the BCM-ETH but not any further than that. Any advice on exercising BACnet modules (preferably without buying $4k of building management software :-) ?
    I'm not the greatest authority on BACnet but I'm was under the impression it uses proprietary objects and commands that cannot be accesed without software.

    The three wire interface sounds like RS 485 using SISO shift registers.

    Im not sure to what level your planning on testing these controllers and components but if you can isolate the hardware issue and force outputs buying the needed software may not be practical.

    It sounds like some of this stuff is pretty old.

    Also those PLC modules would be removed with the old program intact. If it were me I wouldn't offer used modules or used PLCs unless the customer specifically asked for them and understood the potential problems of installing used hardware.
    Last edited by beenthere; 06-06-2012 at 05:53 AM. Reason: price in quote

  5. #5
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    Look in the controls section for help.

  6. #6
    I'm not the greatest authority on BACnet but I'm was under the impression it uses proprietary objects and commands that cannot be accesed without software.
    Well I'm not an authority on any of this stuff :-) but I thought Ibex was the proprietary protocol and BACnet was the "new" open protocol.

    As far as testing, The Plan is to build some test fixtures and essentially lie through my teeth to each module, making it think it's part of a complete system when in fact it's only talking to me. That way I can provide any input signal, issue arbitrary commands, and monitor all outputs. For instance, with the 653 (which I don't want to harp on, but it's my one success story so far) I commanded each digital output on and off, and verified that the associated triacs turned on and off. Then I looped the analog outputs back to the analog inputs. I ran the analog outputs up and down, and verified the associated inputs followed. So at this point I've tested everything except the Microset interface and the comm trunk. I'd like to test those too, of course.

    The TDS software allows me to clear the program in the module so there's not a problem of sending programmed modules out.

    Yeah, a lot of it is pretty old but apparently the Powers That Be think there's a market for it. I'm just a guy, who works for a guy, who has a customer, who claims to have customers, who are interested in having these things fixed. So I'm quite a few layers away from any actual HVAC installations...

    Ultimately I'd like to have a fixture that I can plug a module into and test that module independently of anything else. So, rather than Envision connected to APEX, connected to Tux, connected to Microset I'd just have e.g. a Tux connected to some custom stuff and a PC. The tux would THINK it's connected to motors, sensors, a Microset, and so on but it would all just be lies. Sort of an HVAC Matrix.

  7. #7
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    With out a base program for these modules, especially the PLCs the best you can do is lie to them and test out puts both digital and analog. There should be enough information on analog inputs, sensor resistance scale etc to simulate inputs but without a way to write the programing you're still just verifying component level operation


    And if thats the extent of your testing it sounds like your knowedgable enough to do that without an extensive test bench.

    Actually 20 years ago I would have killed for your job. Most of my old builds are packed away in big tupperware containers in my garage.

    Creating a universal HVAC control model with rheostats, dpst switches and loads for both the digital and analog outs plus time clock function, etc without some knowledge of HVAC building control just sounds next to impossible to me.

    It doesnt sound like you need to go to that extent unless your boss is mandating it.

  8. #8
    ...without a way to write the programing you're still just verifying component level operation
    Do I need to do more? If the inputs and outputs work and I can talk to the processor, what has gone untested? Does the program on the module do anything I can't access by talking directly to the ports without any program loaded?


    Creating a universal HVAC control model [...] without some knowledge of HVAC building control just sounds next to impossible to me.
    I don't care what the various functions do in an HVAC system; I just care that they work. For example, an analog input might be used to monitor water level in a tank, air pressure in a duct, or temperature on a thermocouple. Or something else entirely, I dunno. But to me it's just an analog input. I want to know, when I feed it the lowest voltage in its range, does it report its lowest reading? When I feed it the highest voltage in its range, does it report its highest reading? And proportionally in between? I don't care what it's going to be used for in HVAC.

    And the complexity isn't much of a problem either; a 2 two dollar microcontroller can output and measure analog voltages, plus it has digital IO and connects to a PC over USB. Now THAT needs a program, but that's the sort of thing I do well.


    Actually 20 years ago I would have killed for your job.
    Ah, so you're familiar with our interview process, then :-)

  9. #9
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    Quote Originally Posted by Ghlavenka View Post
    Do I need to do more? If the inputs and outputs work and I can talk to the processor, what has gone untested? Does the program on the module do anything I can't access by talking directly to the ports without any program loaded?
    I wasn't sure to what extent you planned on testing these modules. It was a long busy day and I may have missed some of your previous post. If you can verify operation down to the component and verify comm's then it sounds like you've made a successful repair.



    Quote Originally Posted by Ghlavenka View Post
    I don't care what the various functions do in an HVAC system; I just care that they work. For example, an analog input might be used to monitor water level in a tank, air pressure in a duct, or temperature on a thermocouple. Or something else entirely, I dunno. But to me it's just an analog input. I want to know, when I feed it the lowest voltage in its range, does it report its lowest reading? When I feed it the highest voltage in its range, does it report its highest reading? And proportionally in between? I don't care what it's going to be used for in HVAC.
    You sure you don't want to dedicate a considerable amount of time studying the multitudes of HVAC building control applications and then mocking up a test bench that replicates all of the out put loads and inputs and allows you to make programming changes ? For realism purposes be sure to add a BACnet web server module so the damned thing can E-Mail you 20 times a day with alarm updates.
    Also the graphics are pretty cool too. j/k.....I get it.

    Quote Originally Posted by Ghlavenka View Post
    And the complexity isn't much of a problem either; a 2 two dollar microcontroller can output and measure analog voltages, plus it has digital IO and connects to a PC over USB. Now THAT needs a program, but that's the sort of thing I do well.
    I have more experience with Johnson Controls DX 9100 modules.
    I never had to replace one but when it came to programming they were very tedious. We inherited a building that had a couple of DX 9100 8454s Controlling a water cooled chiller, tower, air handler and pumps.

    Customer kept it for a year and then sold the place. New owners brought their own guys who ripped out the DX 9100 modules and sent them back to our shop. We couldn't give the damn things away.

    If your boss brings in a box of those expect to sit on them for a while.





    Quote Originally Posted by Ghlavenka View Post
    Ah, so you're familiar with our interview process, then :-)

    Good luck with your endeavors. I was thinking about my last project using CMOS IC's to build a signal generator so I would have a reason to play with my old 100 Mhz Tektronix oscilloscope.

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