# A junction model is missing or behaves like the wrong model

Check .MODEL spelling, model names and parameters before changing device physics or simulation settings.

## Compatibility

2.9.0 release target; review-build/source evidence

Published guidance with release-applicability limits. Confirm package applicability before following this guide.

## Check the definition

1. Write the directive as .MODEL, with no space between the dot and MODEL. A malformed . MODEL line was responsible for an older support report.
2. Check that the model name on the junction instance exactly matches the defined name.
3. Verify the documented model type and name=value pairs, parentheses and unique component names.
4. Read the parser/run diagnostic before comparing the waveform.

## Generic example

```text
.MODEL JJMOD JJ(RN=10 CAP=2.5p IC=1m)
B1 1 2 JJMOD area=1.2
```

## Verify the intended model

Use a small circuit with known bias and output requests. Older parser behaviour must not be treated as proof of current fallback semantics; require an explicit valid definition.

## Sources and verification details

Recorded inputs/builds only. Complete walkthrough and final-package acceptance remain separate.

- VAL-008: Installed JoSIM-Pro 2.9.0 Windows. CLI valid-model control and spaced-directive rejection One generic circuit, not all model families.


- support:SUP-012: Generalised editorial finding; outcome qualification retained
- josim-pro:docs/manual_source/sections/troubleshooting.tex: Netlist syntax, component definitions, and model lines
- josim-pro:docs/manual_source/sections/syntax.tex: Josephson junction and model definitions
- validation:windows-cli-20261102: VAL-008; scope and limits recorded
- owner:technical-review-20261102: JoSIM-Pro 2.9 chosen as the public starting path; release availability must be checked before publication

- Support history informed this draft. Current-source guidance has been checked; a fresh walkthrough on the intended distributed release and product-owner review remain pending.

## Related guides

- [RN, R0 and temperature give unexpected junction resistance](/knowledge-base/josim-junction-resistance)
- [JoSIM®-Pro reports that the matrix has no solution](/knowledge-base/josim-singular-circuit)