10" Searchlight circuit board question

[MikeP]

About 6 years ago I overhauled the searchlight which did not function at all due to a burnt out diode. I paid the 69 cents for the diode, paid the 5 bucks for shipping, installed new clutches, adjusted everything and the light worked perfectly until last week. Once again it would not function at all. The unit was getting power but neither the light nor the rotation/elevation would work. I pulled the light and found that the gold thingie in the middle of the board had burnt one of it's ends off.

So...what is that thing? I assume it's available at mouser/wherever like the diode was but I suspect it's more than 69 cents! NOTE: I am not an electronic circuit guy but I'm a great solder-er on them and multimeter user!

Here's a close-up crop of the thing - you can see the burnt end.

 

[rhprop]

That is a 5 ohm 25 watt power resistor and you have more problems than a burned resistor for this thing to go south. I am not familiar with your search light but it is probably in series with that transistor that is shown and that is probably driving the motor or a clutch or both.

 

[MikeP]

Thanks I'll order up the appropriate resistor and go from there...

The circuit board's function is to take the incoming 32v and convert it to 12V to run the motors. The only thing that runs on 32v in the searchlight is the bulb. As I mentioned, I found a cracked diode on that board 6 years ago. Seems an odd setup - using 32v for the bulb but 12v for the motors. Seems like 12V all the way round would be better but, of course, that would call for much heavier gauge wire to the searchlight.

 

[stewart]

Hi Mike, I changed my spot light to all 12 v supply, light bulb and motors
I still have the old circuit board if you need parts.
Cheers Stewart

 

[Trojan]

That resister is a precision 5 ohm, wire wound at 1% at 25 watts. The 1% ratting is going to make it expensive. Give Fair Radio in Lima Ohio a call. They have lots of old military parts surplus. Maybe you will get lucky.
Just checked on the net found some 8 ohm at $6.25 . Not as costly as I had thought. Look around at Dale sights. You should be able to find one.

BILL

 

[OBXTucker]

I have a spotlight that's never worked since I've owned the boat (can't recall the name right now), but I'm thinking about trying resurrect It this winter. Beautiful big light and Its a shame to keep it covered and never have it available to use.

Interesting sidenote. The spotlight was shipped to the original owner while he was in the Med doing a circumnavigation on Kismet (Liberty III at the time). I have letters and price quotes from the light companies to the owner. This was back in the early 80's. Apparently there were some articles written about the trip, but I've yet to find any of them. For you "old timers", the original owner was the president of Fifth Third Bank in Cincinnati. If you remember the boat or owner, Please email or PM me. I'm trying to complete some of her history. Thanks.

 

[MikeP]

Ordered the resistor from Newark yesterday, got it today (standard shipping); can't beat that. I found that the old resistor was not firmly mounted to the large heat sink - it was kind of floating there so I suspect that was the reason for the burn out. I'll install it tomorrow.

 

[OBXTucker]

Mike, I'm headed down to the boat for the weekend tomorrow morning And will take.some pics of my spot. I'm curious if we have the same product, since the boats are the same era.

 

[MikeP]

Thought I'd update this because my last post indicated a completely wrong "solution."

"That is a 5 ohm 25 watt power resistor and you have more problems than a burned resistor for this thing to go south"

That message was from Rhprop and was exactly right. It wasn't the resistor though the resistor had burnt out. I put in the new resistor and it went up in smoke. SO I ordered 3 of every electronic part, (but just one new transistor). THe total for everything except the transistor was about 10 bucks. The transistor was 40 bucks.

So I unsoldered each component, checked them and discovered that one of the diodes AND the transistor were defective. I replaced everything with new parts, connected it and turned it on. Searchlight operated for maybe 10 seconds and the circuit breaker popped and the board's wire wound resistor was extremely hot.

I was puzzled because all parts were new and correctly assembled. I then discovered, looking under the circuit board (about 1/16" between the bottom of the board and the metal heatsink to which it is mounted) that there was a bunch of crud between parts of the board and the base. The crud was directly underneath some of the board terminals.

I cleaned all the grunge out, rechecked all the components with a multimeter to ensure they were still OK, connected the light and it works perfectly. So obviously the grunge was somewhat conductive, grounding part of the circuit. WHether the grunge caused the problem initially or formed later, I don't know but, as noted, there was certainly more wrong than just a resistor. Additionally, prior to the unit's failure a few weeks ago, the transversing mechanism was moving very slowly and it sometimes took multiple attempts to get the unit to move at all. After doing the electronic work and cleaning/relubing the little gearboxes and oiling the motors, it will now elevate/traverse quite well with the on/off switch at the minimum "on" position.

I recall that when I first overhauled the then non-working light in '04 I decided that due to moisture, etc, the light/motors/gearbox should be cleaned/lubed every couple of years. Of course, I never actually DID that!