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Author Topic: Looking for TM751 diagnostic tips and or Schematic  (Read 507 times)


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Looking for TM751 diagnostic tips and or Schematic
« on: December 05, 2017, 09:32:32 PM »

I have 2 failed PowerHouse TM751 

1 is completely dead ... the other tends to continually broadcast a dim command if it receives a dim command (which basically wipes out any other x10 signals) plus the relay appears to turn on OR off for any on OR off command for any address in the same house code range

Both of these failed units have a HT10096A version main board ... neither appear to have any over heating damage (never use the appliance portion of these devices due to being restricted to address 1) ... both of these devices have also always been plugged in to a commercial grade UPS so should have been protected from any Hydro fluctuations ... I couldn't find a whisker fuse or any other form of fuse on either of these boards so not sure how these devices passed UL/CSA certification without containing a fuse. A search on the FCC site for this device (FCC ID: B4S TM751) also turned up nothing

Regardless, as long as an X10's MCU chip isn't electrically damaged or hasn't lost its programming, the device should normally be repairable ... I have used an isolation transformer with a down stream variable transformer which I have used in the past to power up and repair X10 devices but this process take much more time without a schematic or tips from anyone who may have found and resolved issues before ... there was a TM751.gif schematic file on one of the forums, but its link is long dead

Would anyone still possibly have a copy of this gif file they would care to share and or any service tips/mods pertaining to this device?

Brian H

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Re: Looking for TM751 diagnostic tips and or Schematic
« Reply #1 on: December 06, 2017, 06:37:33 AM »

Welcome to the X10 Forums.
I may have corresponded with you on another forum {maybe as BLH}. Asking about the TM751's
I should have the files you are looking for.
I would suspect the most common things that fail. Power supply capacitors, open or shorted diodes. Some of X10s designs didn't have conservative ratings on components.

One point on an UPS. Most of them have AC input conditioning. This frequently acts like a power line signal sucker.
I have burned out a TM751 on a modified sine wave UPS. When running on back up power.

You mentioned an FCC Database Number. So it is probably an earlier model. The latest ones the labels now say Tested to Comply With FCC Standards and have the surface mounted RF receiver IC daughter board.

If you have not seen Jeff's Troubleshooting Tutorials.
« Last Edit: December 06, 2017, 06:52:18 AM by Brian H »


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Re: Looking for TM751 diagnostic tips and or Schematic
« Reply #2 on: December 06, 2017, 07:40:29 AM »

... the other tends to continually broadcast a dim command if it receives a dim command

I haven't seen this complaint in a long time. It goes back about 15 years when it was a major issue for a brief period. I dubbed it the Endless Dim Syndrome. It seemed to be caused by the 120kHz PLC signal being radiated by the household wiring inducing the TM751's super-regenerative receiver to oscillate. The PIC microcontroller apparently assumed this reception was another Dim and acted accordingly. Most people were able to 'fix' it by reorienting the antenna and/or moving it to a different outlet. In my tests, I could induce it at will by changing the antenna alignment with an extension cord on my test bench.

Dan Lanciani offered replacement PICs which solved it for those able to solder. This seemed to confirm it was due to poor programming practices at X10. Sadly, Dan's no longer with us so his PICs are no longer an option.
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Re: Looking for TM751 diagnostic tips and or Schematic
« Reply #3 on: December 11, 2017, 12:01:02 AM »

Thank-you for all the excellent replies ... I found the issue with my dead TM751 by doing side by side comparisons on the bench ... ZD6 the BZY97C18 18V Zener wasn't doin its job any more ... both the PIC 5V rail and the 18V rail were MIA ... had purchased 1N4746's a while back which I have successfully used in the past to repair X10 Modules ... also replaced the 2200 250V cap which as this acts as the main voltage dropping device in transformerless applications (I used to use caps in series with leds back in the early 80s to replace neon panel lamps ... they lasted forever).

I connect X10 devices through an isolation plus auto transformers with the output set to around 40VAC which is a high enough voltage to test the internal components without the risk of getting any serious shocks when getting up and personal with these jam packed devices

As to the Power Backup mode for UPS's ... yes ... if they are consumer grade typically the best they do is make 120V Square Waves which will deliver nasty harmonics and almost instantaneous current spikes to poorly rated components.
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