Repair NASA Marine Echo sounder

[SmileyGer]

Hello,
I have an echo Sounder Target from NASA Marine and a problem.
Inside there is a resistor which is burned down. No chance to get the color code.
Now my question:
Does anybody know a source to get the circuit diagram or
does anybody have the same echo sounder and can tell me which value this particular resistor has (resp. the color code)?
Or any other idea to get the correct value?
Attached there are two pictures with a circle around the particular resistor position.

The sounder was built 1992 (found on the PCB).

Thank you for your help (I hope so)!

In advance,
Christian

 

[OLIVE2222]

Can you please provide a components side picture?

 

[KrisBlueNZ]

Hi Christian and welcome to Electronics Point

I doubt you will find service or technical information. We might be able to estimate the value if you post a photo of the top side of the board.

 

[SmileyGer]

Good morning to all,

Thanks for your replies.
Attached you find the pictures, also from the "resistor".

 

[OLIVE2222]

Thanks for the pictures, still need a picture of the 3 pins component with the cutted metal tab (or the references)
what's the exact failure?

 

[Gryd3]

Are there any components behind the LCD screen? There is a small plastic square on the trace-side of the board beside where the resistor was pulled that may need to be temporarily removed to get a clear picture of what that resistor was connected to.

 

[SmileyGer]

Attached more pictures.
The exact failure is: Switch ON, only 8888 on the LCD, no reaction when pressing one of the three push-buttons.
More infos: The burnt resistor is connected via resistor (approx. 1 Ohm) and a diode to Vcc+.
Under the LCD is only a huge IC.

 

[KrisBlueNZ]

Looks like the transistor is a Motorola / ON Semiconductor BDX33D: Darlington NPN, 120V, 10A. You should check it for short circuit - set your meter to resistance or continuity, put the red probe on the centre pin (or the metal tab at the top) and the black probe on the lead closest to the edge of the circuit board. If it reads less than 10Ω or beeps, you'll need to replace the transistor.

Have you measured the resistor you removed? It may still measure correct.

It looks like the resistor is in series between the positive rail and the top end of the little HF transformer that connects to the collector of the transistor. I'm assuming this is the transmit part of the circuit; it will transmit a short pulse of ultrasonic frequency through that transformer, then wait for the response.

Without knowing the duty cycle of the control signal to the transistor, I can't calculate a value, but most likely the transistor will only be active for a very short time, especially if the unit is designed to detect objects at hundreds of feet like the current "Nasa Marine" units do, so the average current would be much less than an amp. So I would try a low value initially - say 0.47Ω. Mount it off the board in case it loses its smoke too.

I think the resistor is probably not the only fault on that unit.

 

[OLIVE2222]

I suggest a 1 watt ratted resistor.

This guy has the same sounder, he can maybe help on the resistor value.

https://www.electronicspoint.com/threads/nasa-depth-sounder-help.157754/

I believe that the Ultrasonic ic is this one:

http://rbsfm.org/Downloads/Datasheet/LM/LM1812.PDF

if you need to order the resistor, I suggest to add the BDX transistor and maybe the 1000µF to the list, as stated by Kris other faults can be present.

 

[KrisBlueNZ]

This guy has the same sounder, he can maybe help on the resistor value. https://www.electronicspoint.com/threads/nasa-depth-sounder-help.157754/

https://www.electronicspoint.com/threads/nasa-depth-sounder-help.157754/
You'd better hope he still has the same email address (imaginations at ntlworld dot com) - that thread is 11 years old! (It's from a Usenet newsgroup.)

 

[OLIVE2222]

Yep, my default mode is set to optimistic !

 

[SmileyGer]

Tomorrow I will look for the resistor, the BDX and the 1000uF and will try my very best.
I keep you up-to-date.
Great forum, thank a lot thus far!

 

[debe]

I know this isn't the circuit of your unit. But it uses the same chip & may be of some help in how it may be set up. In yours there is a power transistor in the transmitter stage.

 

[SmileyGer]

So, here my last entry for this problem.
After I have replaced the resistor (I choosed 10 Ohm), the BDX and the 1000uF, I found the same behavior as before.
The resistor gots hot, very hot, and so I would say the problem is behind the BDX (gate drive).
So I decided to finish this problem. I gave the sounder back with the hint that it isn't repairable.

Thanks again to all for your help.
Maybe I will come back with a next problem

Best regards,
Christian

 

[flippineck]

Could you try a highish value potentiometer wired up as a rheostat, and try the units behaviour whilst gradually dropping the resistance? as a last ditch attempt

 

[AleksDry]

Hallo everyone. I've bought some boat with installed device you talking about. The boat was sold to me through a few hands and I'm repairing it just by guess. Approaching to repair this NASA marine target depth I found two cables with in-hull transducer kit installed on the hull bottom! Connecting one by one I have result from both of them - estimated depth and letter "E" on the left of the screen. Has anyone any idea? Why two? How is this might be? Also if you have some manuals for those devices (on photo) I'll be very grateful.

 

[(*steve*)]

Hi.

It's generally not a great idea to reopen a long dead thread. Usually we'd recommend starting a new thread and including a link to the previous one.

However, while you're here, can you read the value of the resistor that was the problem in the original thread? I doubt it will be off any help, but it will answer a question that has been left hanging for 3 years.

If you can answer that question, I'll move your new question to a new thread and as links between the threads.

I have a suspicion about the reason for the two depth displays. How are the sensors placed on the hull? Do they both point down or do they point a little to port and starboard? If the latter, then they may be placed so as to measure rapidly changing depth as might occur if you were over a reef. Another similar placement might be forward and aft.

 

[AleksDry]

Hi.

It's generally not a great idea to reopen a long dead thread. Usually we'd recommend starting a new thread and including a link to the previous one.

However, while you're here, can you read the value of the resistor that was the problem in the original thread? I doubt it will be off any help, but it will answer a question that has been left hanging for 3 years.

If you can answer that question, I'll move your new question to a new thread and as links between the threads.

I have a suspicion about the reason for the two depth displays. How are the sensors placed on the hull? Do they both point down or do they point a little to port and starboard? If the latter, then they may be placed so as to measure rapidly changing depth as might occur if you were over a reef. Another similar placement might be forward and aft.

Well,beforehand I'm not an electrician so far... But. What kind of data I have to read? I have some multi meter and will try to do best. Regarding sensors, yes, they are a little port and starboard. Tomorrow I'll do the picture. Has this depth meter two plugs for two sensors? From rear panel now I see only one connection, but may be there are two. I need to dismantle some part of ship to review. Regarding manuals. I found on internet a few short manuals for devices and giving them in attachment.

 

[debe]

The sounder only has one input. On some yachts they will mount 2 transducers either side of the keel. This is so when the yacht is sailing & heeling over, the transducer on the lee side is switched in to operation as the keel may be blocking the other one. Usualy in these systems theres a switching module that automaticly selects the appropriate transducer. If this is missing your other option is to fit a switch to manualy change over the transducers.