Cobalt iP Analogue Point Motor Failures

[Ian Morgan]

Our club recently purchased a number of Cobalt iP Analogue point motors to rebuild the fiddle yard for one of the club layouts. Before it was even completed, a substantial number of these failed. They were sent back for repair, but have been returned because "we used a too high voltage supply". The manual states 7-23VDC. I have not had an opportunity to check what voltage the power supply on the layout was providing.

I was given one of the failed point machines to see if I could repair it. On dismantling. it is obvious a component (probably a voltage regulator) has over-heated and exploded. Of the remaining components, one is marked MR6F which is a fast recovery 1A bridge rectifier, probably unlikely to have been damaged. The integrated circuit by the fried regulator has had its part number partly erased, but appears to be an L9110 which is an H-bridge, which sounds reasonable. The small component labelled J3Y is an NPN transistor, good for 40V and half an amp. The final integrated circuit has had its part number completely erased. Does anyone know what it might be? If it is a programmable device requiring firmware, then there is no chance of replacing it.

 

 

Edited June 29, 2023 by Ian Morgan
Added J3Y description. re-loaded image

[RobjUK]

I'd just verify if it's a 5V or 3.3V regulator by checking the output voltage of a good unit, then try only replacing that in the failed ones.

 

There is a fair chance that the reg is the only damaged part; don't worry about the MCU (probably a PIC) unless that is definitely dead - they are pretty bombproof..

 

[Brian]

Posted in error Sorry.

Edited June 21, 2019 by Brian

[John ks]

A quick search(type in Holtek Semiconductor Inc. HT7550-1 datasheet) shows that the number HT 7550 next to the regulator is for a Holtek Semiconductor Inc. 5Vregulator rated at 100mA

John

 

 

[Junctionmad]

Most likely a micro of some type is the part with no Id 

[Ian Morgan]

On 22/06/2019 at 12:54, John ks said:

A quick search(type in Holtek Semiconductor Inc. HT7550-1 datasheet) shows that the number HT 7550 next to the regulator is for a Holtek Semiconductor Inc. 5Vregulator rated at 100mA

John

 

 

 

Thanks for pointing out the thing that was so blindingly obvious that I had completely missed it

 

I have ordered some to try. I also have a working one that I can measue some voltages on for comparison. I will report back when I have the bits.

 

[Ian Morgan]

Received some HT7550 regulators I ordered via eBay. They worked out at less than 20p each, and I have plenty of spare ones now.

 

I removed the charred remains of the one on the PCB using a hot air rework station. I soldered the replacement part using a pointy soldering iron and 0.6mm solder balls. I have not mastered soldering using the hot air gun yet, only dismantling.

 

I may have voided Cobalt's non-existent warranty

 

I reassembled the Cobalt point motor and applied 12V DC to the inputs and, hey presto, it works perfectly.

 

I did take the precaution of photographing the positions of all the gear wheels in case I managed to spill them everywhere.

 

Anyway, thanks for all the help and suggestions.