Products > Test Equipment
Upgrading Mainboard in Lecroy DDA-3000 (aka WavePro 7300a?)
tautech:
200W is pretty pitiful but might be enough IDK.
ollopa:
Typically the power sequencer will hold the CPU in reset until all the monitored supplies are within tolerance or until it detects a fault and shuts off the main power supply. I think what you're observing is the initial turn-on attempt followed by a fault and it giving up. I mentioned mine does the same thing if the +12V is disconnected but in your case it's probably one of the regulated supplies on the MB.
The trick of looking for the hot cap works great if your failure mode is a shorted cap and the MB will stay on long enough for it to heat up. I doubt it will work in this case.
Possibly a good time to consider upgrading rather than repair. That board should have about 50 through-hole electrolytics which you wouldn't want to waste the money and time on replacing all of. On the other hand you could try in-place checking with the old trick of using a signal generator and a scope to evaluate ESR:
http://electronics-diy.com/electronic_schematic.php?id=948
https://www.nutsvolts.com/questions-and-answers/capacitor-esr-tester
https://circuitdigest.com/electronic-circuits/capacitor-esr-meter-circuit-using-555-timer-ic
You get the idea.
Also keep in mind that motherboards are many, many layers thick with large ground planes and no thermal relief, so your old Radio Shack soldering iron is not going to do the trick. It helps to have a variety of tools that can transfer a lot of heat and knowledge of a few techniques.
analogRF:
--- Quote from: ollopa on January 02, 2020, 01:52:29 am ---Typically the power sequencer will hold the CPU in reset until all the monitored supplies are within tolerance or until it detects a fault and shuts off the main power supply. I think what you're observing is the initial turn-on attempt followed by a fault and it giving up. I mentioned mine does the same thing if the +12V is disconnected but in your case it's probably one of the regulated supplies on the MB.
The trick of looking for the hot cap works great if your failure mode is a shorted cap and the MB will stay on long enough for it to heat up. I doubt it will work in this case.
Possibly a good time to consider upgrading rather than repair. That board should have about 50 through-hole electrolytics which you wouldn't want to waste the money and time on replacing all of. On the other hand you could try in-place checking with the old trick of using a signal generator and a scope to evaluate ESR:
http://electronics-diy.com/electronic_schematic.php?id=948
https://www.nutsvolts.com/questions-and-answers/capacitor-esr-tester
https://circuitdigest.com/electronic-circuits/capacitor-esr-meter-circuit-using-555-timer-ic
You get the idea.
Also keep in mind that motherboards are many, many layers thick with large ground planes and no thermal relief, so your old Radio Shack soldering iron is not going to do the trick. It helps to have a variety of tools that can transfer a lot of heat and knowledge of a few techniques.
--- End quote ---
I also thought that it could be one of the on board regulators/dc-dc converters...we'll see
I know how hard it is to replace the caps on motherboards. I recently did that on a FIC503A (Agilent 54845A) and it drove me nuts...
for soldering I have a Hakko and it did the job on that FIC mobo albeit with a lot of pain.
for in-circuit ESR test, I usually use my HP 4263B (I bought it with recent calibration for $440 delivererd about 16-18 month ago ;D ;D)
with 20-50mV rms test voltage. Usually gives a very good indication but of course it depends on the circuit.
unfortunately in case of power supply filters when there are inductors in series between two caps you can never know what you are measuring exactly specially at low frequency ....
analogRF:
for upgrade, what motherboard do you guys suggest?
I am looking for something that fits in place of the original one with no tempering with the scope body and back panel, etc...
and I dont want to change the LCD or anything.
nctnico:
You'll need at least a MB with an Intel chipset and AGP slot so the display will work. The most ideal situation is to simply get the same motherboard.
Still... your problem could be the CPU (or the CPU got fried) so get a new CPU too.
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