Skywatcher HEQ5 Pro won't power up and blowing fuses

[Deeko]

Hello, I have had my HEQ5 Pro for 2 years with no issues. Tonight I went to power it up , and when I turned on the  12V 10A power supply I noticed the red power light was already glowing even though the mount switch was in the off position.

I started trouble shooting as below:

1) Disconnected EQMOD cable from mount and the power light went out (with power switch in off position);

2) Switched power on at mount switch and power led didn't come on and no noise from mount, not found on PC via EQMOD console;

3) Reconnected the EQMOD cable to the mount and the power LED came on, this was with the power cable disconnected and mount power switch in off position - clearly this isn't right;

4) Checked the fuse in the mounts 12v cigarette lighter style cable and it was blown, replaced it, switched on and it blew the new fuse, tried  the cigarette light cable that came with the mount and that fuse blew too;

5) The 12V PSU is powering everything else ok including camera and dew heaters and outputting a steady 13v;

6) Tried two mains 12V DC adapter 5A and 3A and using them the mount power light flickers a little intermittently when switched on, most of the time it didn't come on at all and mount made no noise (it usually clicks and makes a quiet whining noise when powered up);

7) The connector barrel on mount looks fine and not loose.

After reading around the culprit may be the motherboard, maybe someone else has read about some of symptoms above and can maybe provide some pointers to what might be wrong.

ta!

Derek

[MarkAR]

Sounds like some sort of short circuit. 

If the 12v power supply is working fine then it does sound like an internal fault.

I  think you'll need to have a look at the circuit board to see if anything has blown, any burnt areas or smokey smell. Also check the wires for any frayed or chafed insulation.

[Deeko]

Going to look at it today, I have a digital multimeter, I am not the most clued up with electronics so if anyone could provide some pointers on what/where I should test for in terms of continuity etc. that would be great! Gutted about possibly having to spend over £100 for a simple circuit board that looks like it costs a few quid to make.

[Deeko]

Took out the circuit board and 'appears' to be on damage or smell

 

Edited February 23, 2020 by Deeko

[AndyThilo]

Is that a hole in the chip? Bottom photo, top left IC. You can get a new PCB for £100. With the PCB out, check the power input for a short circuit using a multimeter. 

 

[Deeko]

Here is a close up of what might be a hole - not sure if that is actually damage? Also a few photos of what I think may be an ever so slight burn indicator but my eye sight isn't that great to tell! What is that component for that I have marked that may have slight burn damage?

[masjstovel]

Agree it sounds like a shortcut issue since the indicator light was on. Can there have been water intrution somehow? Your power supply is that switchable between tip positive and tip negative? Should be tip positive i think.

If nothing works, you always have this option, cheaper than a new HEQ5:

https://www.teleskop-express.de/shop/product_info.php/info/p9118_Skywatcher-mother-board-for-HEQ5-SkyScan---spare-part.html
 

Edited February 23, 2020 by masjstovel

[AndyThilo]

I looked at one on eBay and it has the same markings so it's not a hole.

[Deeko]

With the board out now, can anyone point me to a guide on what I can test with a multimeter? We have had a lot of rain recently in the UK and the mount may have been in out in it for a few minutes as I have dashed out to get it when clouded over. Maybe II have just lucked out this time and possible some water got in but it was everything is all dry and no sign of any damage. May just need to buy a new board 😕

[blinky]

I blew 2 motherboards, and could not figure out what was happening - basically if anything metal touched the mount, like the outer/ground on my dew band, it blew the board.  After the 2nd one I was determined to find out why...  Im not sure if it was my fault, missing something off when upgrading from non-goto to goto but the screw, in your 2nd lot of photos, the middle photo, that screw, touches the metal of the board when its properly tightened, usually this would be the ground plane of the PCB but for some reason, its sitting at +12v. This meant when everything was connected up, the main chassis of the mount was sitting at +12v as the screw would conduct from the PCB onto the case of the mount.  When anything connected to GND touched the mount, or really the leg of the mount since the mount is painted black, it would short the 12v to ground, blowing the fuse and the PCB!  My solution was to insulate that screw from the PCB with a plastic washer.  I could not see anything blown on the PCB either but without the circuit diagram its pretty hard to figure out the circuit, plus it could be an internal track that blows

Does the above make sense?  Kind of hard to describe!

[MarkAR]

I think you might have found the culprit, by the looks of the pictures, the circuit board is a bit lumpy looking around it.

As for testing, try simple continuity test between the 4 soldering points on it. Tried a google search for the circuit board diagram but couldn't find anything so no idea what the component is. If you have a Maplins local to you, pop in and see if anyone can help.

If Blinky is right, then reassemble and see if you have continuity between the positive power input (centre jack pin) and the body or the screw.

[blinky]

4 minutes ago, MarkAR said:

I think you might have found the culprit, by the looks of the pictures, the circuit board is a bit lumpy looking around it.

As for testing, try simple continuity test between the 4 soldering points on it. Tried a google search for the circuit board diagram but couldn't find anything so no idea what the component is. If you have a Maplins local to you, pop in and see if anyone can help.

If Blinky is right, then reassemble and see if you have continuity between the positive power input (centre jack pin) and the body or the screw.

Maplins!  They closed a few years ago

[TerryMcK]

Just a point. Maplin only exists in a very minor form now as a website so no stores anymore. 

[MarkAR]

1 minute ago, blinky said:

Maplins!  They closed a few years ago

Damn, thought it was just a few shops that were closed.

[TerryMcK]

yes cheap tat that they ended up selling was cause of their demise sadly.

[AndyThilo]

The main thing to check is that you don't have a short on the DC in, so between the centre pin and the outer ground. If that's shorted then a diode or capacitor inside has failed. 

[Tomatobro]

OK here is what to do.

Find the two power input pins (second plug from the left?) put your multimeter onto Ohms and put the probes across the two pins. if the number is stable take a picture of the display and post it here. If the number is not stable but slowly climbs in value just post that is what it does. (This second condition shows that the multimeter test voltage is slowly charging up a capacitor)

 

[Deeko]

29 minutes ago, Tomatobro said:

OK here is what to do.

Find the two power input pins (second plug from the left?) put your multimeter onto Ohms and put the probes across the two pins. if the number is stable take a picture of the display and post it here. If the number is not stable but slowly climbs in value just post that is what it does. (This second condition shows that the multimeter test voltage is slowly charging up a capacitor)

 

I followed the wires from the power switch on the mount and they appear to be connected to the two pins on the connector in photo (red box). I then put the multimeter on them for ohms and the number started to rise.

[AndyThilo]

Test both pins to a ground (usually the metal surrounding a screw hole). One will be short and show 0 ohms, the other should be open circuit. 

[Tomatobro]

Looking at the picture the connectors (left to right) are 4 pin, 2 pin, 6 pin, 4 pin and 6 pin. have I got that right? And the connectors look like JST types.

Looking at the other pictures there is a choke and two electrolytic capacitors in the general area of the two pins so I am guessing that the two pins you tested are indeed the power input. That being the case there is no dead short across these two pins.

If it were me I would put the board back in and then just connect the plug on the far right and apply power. If the fuse does not blow disconnect the power and put another plug in (leave the first plug in place) and power up again. If the fuse does not blow keep repeating this procedure untill either a plug connection takes out the fuse or all plugs are in and the fuse remains intact. Post the results when you have them

 

[MarkAR]

If its a capacitor that failed, sometimes you can visually see a bulge or split in it. Could be C3 near the pins.

Edited February 23, 2020 by MarkAR

[Deeko]

24 minutes ago, AndyThilo said:

Test both pins to a ground (usually the metal surrounding a screw hole). One will be short and show 0 ohms, the other should be open circuit. 

both pins have resistance values

[DaveL59]

bear in mind from a post earlier that the screw may well be 12v +ve rather than the 0v rail, hence a short when you touch an earthed item to the mount body.

You'll need to trace the 2 pins along the board and try to determine which is earth (likely one goes to the -ve on one of the capacitors and then onward from there).

[AndyThilo]

31 minutes ago, Deeko said:

both pins have resistance values

What value?

[Deeko]

Thanks for all the help folks, think I am ready for throwing in the towel with this one and buy a new board. Is there any kind of protection that can be fitted to the mount switch to stop the board from blowing again in the future? More to the point why doesn't it have any protection built in now, not exactly a cheap item.