Broken DER DE-5000 TL-21 crocodile clip adapter

[electr_peter]

I noticed that DER DE-5000 LCR meter could complete calibration procedure with TL-21 adapter. "OPEN" calibration showed "PASS", but "SHORT" calibration showed "-00-" for a long time and then "FAIL".
On the other hand, tweezers adapter TL-22 calibrated with no issues.

LCR meter is relatively new and works well, I did not expect any electronic damage to meter itself. Obvious suspect was TL-21 crocodile clip adapter.

External continuity check with multimeter did not reveal anything out of ordinary. TL-21 has sense and force terminal connected/shorted at the base of the crocodile clip, so continuity check passed. By the way, TL-22 also has sense and force terminals connected near tweezers tip.

I opened the TL-21 case to check internal connections. Solder joints between right angle PCBs were cracked for "-" red and "-" white terminals. Cracked joints created intermittent connections and failed "SHORTED" calibration. Cracking could occur because of structural stress on these solder joints - they are subjected to both bending and pushing forces.

See close-ups of solder joints. TL-21 adapter without the case is inserted in DER DE-5000 for ease of photography.

Action plan for repair is obvious:

• Remove unleaded solder, clean joints, resolder with leaded solder. This should improve resistance to cracking.
• EXTRA - TL-21 leads are too short, almost too short to be usefull at all. 4 wire clips are in order - upgrade will add more cable length and ability to check to broken joints (because all 4 wires cn be open when clips are open).

Things to keep in mind

• TL-21 and TL-22 adapter construction (including all derivations) is prone to solder joint cracking and intermittent connections. Check and resolder if needed.
• TL-21 and TL-22 adapter construction does not allow to easily check for cracked joints, because sense and force terminals are always connected.

[electr_peter]

I repaired and modified broken TL-21 adapter with longer leads a while back. I used these 4 wire cables cut in half Ebay, LCR Meter Test Leads Small modification was required to the box to fit four larger cables.

LCR meter is much easier to use with ~40-45 cm lead length and wide crocodile clips. Calibration procedure took into account extra length, no effects to accuracy were noticed. Tendency of solder joints to fracture still remains even after re-soldering with leaded solder.

[h.bashar]

If structural integrity of the 90deg solder joint is a problem try soldering a 90deg thick gauge  copper wire  (or piece of copper foil) between the pads. I have one of these meters and I haven't noticed this problem (maybe because its used sparingly).

[electr_peter]

If structural integrity of the 90deg solder joint is a problem try soldering a 90deg thick gauge  copper wire  (or piece of copper foil) between the pads. I have one of these meters and I haven't noticed this problem (maybe because its used sparingly).

Thanks for an idea, I would do that next time if similar issue were to reappear.

I think that soldering job (if done properly) is good enough to last for a long time, but the construction of TL-21 is problematic and should be improved. Solder is brittle and is the only structural element holding right angle PCBs together (which take considerable stress from insertion/extraction).

[h.bashar]

If structural integrity of the 90deg solder joint is a problem try soldering a 90deg thick gauge  copper wire  (or piece of copper foil) between the pads. I have one of these meters and I haven't noticed this problem (maybe because its used sparingly).

Thanks for an idea, I would do that next time if similar issue were to reappear.

I think that soldering job (if done properly) is good enough to last for a long time, but the construction of TL-21 is problematic and should be improved. Solder is brittle and is the only structural element holding right angle PCBs together (which take considerable stress from insertion/extraction).

I agree, no need for two pcbs in there. if they made the adapter to distribute to 4 normal BNC or banana style connectors it would have been great.