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Dynaload DLF 100-100-1500 (100V / 100A /1500W DC load) teardown & repair

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nctnico:
Look what the DHL courier dragged in:


A beefy DC load has been on my wish list for a long time. I got this for $100 + $390 for shipping from an Ebay seller in the Phillipines.
The DLF 100-100-1500 DC load uses 32 MOSFETs to dissipate up to 1500W. It can do constant current, constant resistance, pulses and short circuit. The description was 'working but no display'. More about that later. To be honest the DC load doesn't look as huge in real life compared to the pictures. It is a relatively deep 3U unit. The top cover is bend pretty bad. I think the seller turned it inside out to make the device look better. Also some of the buttons don't stay in the depressed position.

The guts:


The primary regulator board which has the control circuitry and 16 MOSFET drivers. Each MOSFET has it's own current regulator so the DC load is basically sharing the current between the MOSFETS.

I love a good bodge in the morning:


The secondary regulator board:


Front panel PCB. I was hoping to replace the current setting pot with a 10 turns one instead of fine/coarse but I guess that is going to take some creativity.


Big ass load disconnect relay:


Current shunt and current amplifier board:


Isolation between the - input and the chassis.  :wtf:


One of the two fans and PSU:


Mains wiring:


The assembly required a hack saw:


I think I have found the reason the displays don't show anything. I'm missing a mains transformer here. I guess the DC load has been dropped which caused the mains transformer to hit the eject button.


Besides cleaning there are a few jobs to do:
1) Source a new mains transformer

2) Test whether the DC load still works. I took some initial measurements and the MOSFETs seem to be OK.

3) Redo the mains wiring properly and switch the two fans in series if they don't need replacement. Also add temperature control to the fans.

4) Take the switches out and see if they can be fixed.

5) Check the accuracy and adjust if necessary

6) Straighten the top cover and reinforce it with some aluminium L or square tube. There is enough space in the casing to add some height to the top cover.

edpalmer42:
It looks like the missing transformer was very low power.  For test purposes, you should be able to bypass it and provide DC from one or more external supplies directly to the capacitors after the rectifiers.  That would allow you to check the rest of the unit without having to source a new, multi-winding transformer.

Ed

nctnico:
It appears the transformer can be bought from Mouser:
https://nl.mouser.com/ProductDetail/Bel-Signal-Transformer/DMPC-Y-15/

I forgot to mention it in the post above but all the manuals (with calibration procedures and schematics) can be found online. I just entered the transformer part value into Google and it came up with Mouser's website.

edpalmer42:
Hey, that's cheating!  :--  Transformers must be custom or discontinued.  Everyone knows that!

Seriously, I don't think I've ever sourced a replacement transformer that easily.  They've even got them in stock!  Hopefully the rest of your rejuvenation goes as smoothly!   :-+

Ed

nctnico:
I'd raise you even more: the LCD panel meters are still available from Newark/Farnell. That is amazing given the DC load is 19 years old and the design itself is probably even older.
OTOH there is also a Burr-Brown multiplier chip on the board (the golden one) which is obsolete. The multiplier is used to calculate the total power dissipated by the load and shut down in case too much power is dissipated.

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