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HitechAstro Serial to USB for EQMOD - DIY repair

GeekTeacher Astro

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GeekTeacher Astro

Hi All


I searched the forums on a couple of keywords for anything on this topic but drew a blank, so I'm hoping it's OK to start new topic.


I managed to short the input on the 12v cable going into my HEQ5 Pro mount and it seems to have blown the motherboard. This was very kindly checked by Graham Holmes for me who confirmed it was dead, even though the red power light on the mount still works.  Graham replaced the capacitors which often cause problems but it didn't cure it. I didn't know there was a problem until I tried to connect the mount to my laptop via the HitechAstro cable and got no response. I then inserted the SynScan handset and got an 'Dec/Alt no response' message indicating the motherboard problem. The mount has now been sent off to RVO for a new motherboard and service.


But I have another issue which that is my HitechAstro Serial to USB cable is no longer being recognised by any computer I put it in. It should come up in Windows Device Manager as an available port whether or not anything is connected to it.  So I'm assuming the short has damaged this as well - although it wasn't inserted when the short occured, it was put in at a later time, probably after the damage was done. So I have a number of questions:


1) Would a faulty motherboard have caused damage to the serial to USB cable?

2) Is there any chance it can be revived or repaired?


Assuming the worst I've already bought a cheap USB to serial cable which looks very similar to the HitechAstro one (see photo below). It has a Prolific PL2303TA chip in it and I hope to make this into a replacement, but I need to know a few things:


3) The adapter I bought works at TTL (5v) and comes with a warning about this (see below)  Does the HitechAstro one use 5v TTL logic?

4) What is the pinout of the HitechAstro cable at the RJ45 socket end? The coloured wires are different but I have been given the data for the new cable (see below).


I have an RJ45 crimper and plugs, so I'm hoping just to crimp a plug on the end of this cable - all I need to know is the wiring that the HitechAstro cable uses. The photo shows the replacement USB to Serial cable (Prolific 2303TA), the RJ45 plug I want to crimp on to it and my original HitechAstro cable plug. I just need to know the pinout of the coloured cables in the HitechAstro plug.


It comes with a warning about the device being TTL (5v) and I need to know if this is OK for the HEQ5 Pro mount.


Chip : PL2303TA

Connections : Red +5V, Black GND, Green TXD, White RXD

Warning, this is a TTL (i.e. 5V) device. Connecting this device to standard RS232 connections WILL destroy it and void the warranty


Thanks in advance for any help I can be given.





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Answer to question 1, quite possibly. 

Answer to question 2, unlikely.

Answer to question 3, if the Hightec cable plugs into the mount handset socket, then as far as I'm aware the interface is not RS232 levels but whether they are 5V or just 3.3V compatable, I'm not sure. And I don't know if the serial interface follows the normal RS232 mark/space polarity.

Answer to question 4, no idea of the pinouts but if you have access to an oscilloscope, then using the handset you could check which is Serial In and hence by default which is Serial Out (and also check if the voltage levels provided by the handset are the same as given by your new cable).

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Why don’t you try and e mail Dave Jackson at hi tech Astro and ask the question? He may be able to help?

Think there is an e mail on the website you can use

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